Another Thermostat Adventure
 

So last Saturday I bravely decided to change the thermostat on our '82 300SD. There was a slight leak around the thermostat housing on a cold start. I received the thermostat and the o-ring. First thing I did was apply WD40 to the three nuts on the housing, and repeated the process (you know what is coming) I honestly looked very hard for the radiator drain plug but I still have not found it. I ended up draining the radiator by slowly letting the anti-freeze pour out of the bottom hose. Back to the housing itself. Two of the nuts were a breeze to turn, but one was badly rusted. More WD40, turn it a bit in and out. Wait. More turning and WD40. In the end the bolt broke off. Saturday afternoon and our only mode of transportation has an inoperable thermostat housing. I tried the vise grip method and the "cut a groove in the bolt and use a screw driver" method. No luck. I got a lift to the Auto place and bought an "extractor" set, and optimistically, a new set of bolts. Spent the rest of the Saturday afternoon trying to extract the broken bolt, but no luck. I learned that no amount of cussing and swearing, in any language, will help move a rusted bolt.

On Monday I borrow a friends car and drive to a local scrap yard that Willrev from this forum recommended. By a stroke of luck they have a 300D with a matching thermostat housing, dirty but in a sound condition. My first experience with "pulling" spares. After cleaning it I install the new thermostat and o-ring, fill up the anti-freeze and pat myself on the back. I go for a test drive and the heat climbs alarmingly. Drive back home and start the first of many searches on this forum for "burping", overheating, new thermostat... you get the idea. I let the car stand on an incline with the heater on and expansion tank cap off, while shaking the car up and down and singing a jolly tune, just one of the various methods I gleaned from Diesel Discussion.

On Tuesday I am sick of the car and wife takes it to work, but she has instructions to park on a steep incline. No luck, still overheating. By this time I think I have just about read every post and discussion on the subject on this forum. Wednesday arrive and after more attempts at burping the cooling system, I take out the new thermostat and install the old one. Lo and behold, the temperature is back to "normal". No need for any burping. I say "normal" because in the five years we had this car the temp reading on the gauge would be very low. There is a line about a third of the way between 40* and 80*, and normal running temp has always been on or a millimeter above that line. With the new thermostat the needle went close to the 80* mark. While I was looking at the many posts on this subject I thought that my aux fan might be part of the problem, so I did the test where one shorts out the a/c drier (pressure?) switch, and the aux fan did work. I got the advice to short out the switch with a 30 amp fuse to protect the rest of the circuit.

My questions
- I thought I might have an obstructed radiator, but wont this cause over heating even with the old thermostat?
- The ambient temp is around 45-55*, how long will it take before the lower radiator hose starts to heat up? I did about 10 minutes at 70 mph and the lower hose was still cool, although the engine did not over heat.
- On the thermostat housing there is a temp sensor. I read that by grounding that cable, the aux fan should come on. Mine doesn't. I am grounding it on the engine block. How can I test this cable?
- Last summer I started having problems with overheating while driving in town with the a/c on. Do I have a bad "ice cube" relay, or should I look somewhere else?
- Should I take my neigbours advice and take the ole girl out into the back pasture and put her out of her misery? I think he is sick of seeing me just standing there, frowning at the engine compartment. I tried to tell him that a lot of what I do is "preventative staring", but he is not buying it.

It is probably glaringly obvious that I am a newbie, so I apologize for any miss named parts and/or terms and general ignorance. :o

Regards
Wessels

The only really dumb question is the important one you DID'NT ask.

When my thermostat failed recently, my coolant temp stayed around 60C. With a new (used) one, it's back up to 80-85C where it should be.

Your temp gauge shoule be at or over 80 at normal operating conditions. If that's the only problem, you don't have a problem. My SD runs at 82 or so in the winter and 90+ in the summer - it's within the safe range.

I sympathise with you on your t-stat housing - I had screws break off as well. I drilled them out and used a nut and bolt all the way through to hold it on.

Don't worry about being a newbie - we all were at one time. I still am humbled by the lack of knowledge I have and the wealth that others on this forum have.

Thanks for the fast replies and advice.
I am worried that my temp gauge is not showing an accurate temp reading, thus the panic when it went up so high after replacing the old thermostat. I should probably get the car temp tested and go from there. Do you think I should put the new thermostat back in? I always thought a bad thermostat will cause overheating. Live and learn, he?

put the thermostat in hot water to make sure it is functioning right before you install. 80-90c is about where it should run. You might want to remove your radiator and give it a good cleaning but by no means at all should you take your neighbors advice.

If your temp. guage is reading about 80 it doesn't have a problem. ;)

By the way, what does the neighbor drive?

With that mileage, you are only at mid-life. :D

I don't run thermostats in any of my cars and I never have. I simply use a 'hollowed-out' thermostat body, which serves as a sort of restrictor, but will never fail and overheat the engine.

I find my heater performance hot enough to be uncomfortable and engine coolant temperatures hovering around 160° to 175° on a 100° day.

Our coldest winter day here is about 30°F and the average is in the mid 40° range overall.

My 440 Cubic Inch Pontiac with 9.00:1 compression runs at a consistent 155° on 100° days and doesn't get over 175° in traffic with the A/C on.

Never had any adverse wear issues and oil/crankcases are just as clean as those engines I have disassembled that ran a thermostat.

I feel your pain over the broken bolts.... :mad:

Another one of my modifications on all my engines is to replace ALL the bolts/studs/washers in the Coolant and Exhaust Systems with Stainless Steel and a liberal application of Wurth High-Temp Antiseize Lubricant.

On my 300SD, I actually changed every bolt/nut/stud on the outside of the engine over to Stainless Steel, including the Motor Mounts, Vacuum Pump, Oil Pan, and Accessory Mountings. All the washers were replaced with Stainless Steel too.

I even found Stainless Steel Acorn Nuts for the Camshaft Cover...Bert

If the "old" thermostat was stuck open or was opening early the temperature would probably stay around 60deg. unless it was really hot outside or you are climbing lots of hills. The thermostat should open at about 80-85deg. which is the normal operating temperature for these cars. Your auxilliary fan would not come on at these temperatures. Unless you are in the 95-105deg. range I wouldn't worry. ;)

Thanks again for the responses.
So what you are saying is that the temp reading that I am getting is correct, so just put in the new thermostat already. I will probably do just that over the week end. I will also get a thermometer to do the boiling water test on both thermostats. I do not want to over heat this engine. I have grown VERY fond of it.
SD Blue: My neighbour drives an American Generic sedan. I am not completely sure which one. I still get confused with US designed cars. I hope he was just joking.
Doktor Bert: Good idea to change all the bolts to stainless steel. I am not sure that I am brave enough to get completely rid of my thermostat, yet.

I have to take issue with 2 things here. I would NOT remove the thermostat unless you have a specialized purpose in mind, like drag racing. The thermostat in your SD, which typically fails by opening early, has an intended purpose. It reaches ideal operating temperature quickly and maintains it, for the benefit of the engine's reliability and passenger comfort (heat). Second, I would warn you NOT to replace your fasteners with stainless steel ones. Stainless fasteners are typically 18-8 stainless, a soft, austenitic metal. While you might avoid some corrosion problems, you introduce a few others. Stainless steel is notorious for galling, especially in aluminum. This feature alone leaves you in a undesirable condition when you load the fastener up with anti-sieze and tighten it. The threads deflect much more than they are intended to against the hole (and deflect the threads in the hole as well) Torquing fasteners under ideal conditions has enough variability in it, but the same torque value can easily provide too much preload. Reducing the torque to compensate can cause the fastener to loosen and fall out. Moreover, many of the fasteners on the 617 are allen heads (like the M6 screws holding the upper oil pan and the vacuum pump) The 60 degree pressure angle on the head is frequently not strong enough to withstand the forces needed to tighten and later loosen it. In other words, they can cam out. Hell, even the alloy steel screws can cam out under certain conditions. If you remove any corroded screws by all means replace them, but with original type, cad plated, alloy steel screws. PLEASE! :eek:

Thanks Pete
I am finally seeing the light :rolleyes:
"The thermostat in your SD, which typically fails by opening early..." seems to be exactly what is wrong with my thermostat. Also thanks for the advise on not changing to stainless steel bolts. Running the car without a thermostat was never an option.

The Mercedes Shop manual specifically forbids running the engine without the thermostat.....
The thermostat may have two different opening temperatures... on one thermostat..
I have posted the pictures from the shop manual on other threads... probably the one by " warden' if you want to look them up.

Grade 8 Stainless is available. I took all these maters into consideration many years ago when I started using SS fastners. No reduction in torque is required.

I also test bolts in a batch by torquing them to the breaking point and recording the force required. So far, they have performed in identical fashion to plated Grade 8 Fastners.

Over the years, I have installed SS fastners on literally hundreds of engines with positive results.

As previously posted, one should check the material used in the production of the fastner.

Also..I don't use thermostats in my own vehicles. I simply install a hollowed-out thermostat body that will offer slight restriction to coolant flow in exactly the same percentage as the stock thermostat at full open.

All engines build a certain amount of residual heat and they will create this heat energy no matter what action you take.

Thanks for the informative post...Bert

One thing I thought worthy of mention is the reasoning behind not using a thermostat.

First of all, let me preface my statements with the fact I do not own a normal car and you should keep that in mind as you read this post.

My 1979 Trans Am W72/WS6 is one of only 1,107 produced with that option package. It is powered by a hybrid 7.4 litre OHV V8 (.060" overbored 400 4-bolt main block with 1962 Pontiac 421 Crankshaft) producing over 450 horsepower on 92 octane pump gasoline.

I designed the camshaft myself and it uses a Ford (1-3-7-2-6-5-4-8) Firing Order as opposed to the Pontiac (1-8-4-3-6-5-7-2) Firing Order to redistribute main bearing/crankshaft loads at high rpm.

Coupled with a close ratio 4 speed gearbox and 3.42:1 axle ratio with 4 wheel disc brakes, the car can accelerate from 0 to 100 mph and back to zero in around 15 seconds.

I drive this car to work a couple of days a month and it is an absolute monster. ;)

My 1978 300SD is also a hybrid of sorts. The block has been deck to minimum thickness, the valve events have been optimized for performance, injektor delivery has been raised to the maximum specification and the injektor pump has been altered to maximize performance.

The turbocharger has been extensively modified and even the oil passages have been enlarged and polished to a mirror finish, the same treatment we give our competition engines.

To say the least, this is not your average daily driver.

On a dynometer, we have recorded substantial increases in horsepower and torque production with reduced engine coolant temperatures. Most of the upgrade ECM 'chips' also include a low temperature thermostat for this reason.

The second reason is mechanical reliability; if you don't have a thermostat, it cannot possibly fail.

Lowering coolant temperatures affects piston crown temperatures and inlet air temperatures, all of which have a dramatic influence on performance. On gasoline engines, this allowed the use of a more agressive advance curve giving better performance out of the corners in endurance applications.

On my street-driven cars, I employ this practice for many of the same reasons. Less heat equates to less thermal load on the engine and its oil, lower cylinder wall and camshaft wear and less stress on the cooling system.

Exhaust Gas Temperatures are also lower.

The biggest reason manufacturers run high coolant temperatures is to improve exhaust emissions. I personally prefer decreased wear as an alternative.

Engine oil remains as clean in my 617 as those with equal mileage running a thermostat. My temperature comes up quickly and heater performance is excellent.

In short, my coolant temperatures (in Central California) run within 30° of what they would with a thermostat. The difference is my car will never leave me stranded on the side of the road because of a stuck thermostat.

In the average commuter vehicle with Electronic Engine Management, I do not advocate removal of the thermostat since the engine controls are temperature dependant.

If you choose to run a thermostat in your engines, you should use a high quality replacement of the proper temperture range for your engine. You should also run the correct percentage of coolant to distilled water.

I am simply sharing with the forum what I do on my vehicles because I have enjoyed great success with these practices. I am not suggesting members implement my modifications, but I think the varying mechanical opinions give a rich informational database to the discussion in general.

I will say that I have removed the thermostat on a number of customer's 617's (with their consent) and replaced it with the hollowed out restrictor. In every case, they were pleased with the reduction in engine temperatures and mechanical reliability in our temperate climate.

Keep in mind summer temperatures exceed 100°F and winter temperatures rarely drop below 32°F.

I also inflate the tires on my vehicles with Nitrogen as opposed to air, because it allows tires to run cooler at sustained high speeds.

What won us races on Sunday, I used in my personal cars on Monday.

Not for everyone, but its hard to argue with success...Bert

I am not suggesting members implement my modifications, -OK, at least we can agree on this. Also, instead of nitrogen, why don't you fill your tires with pre-heated air. Seems like you have all you'll ever need and then some. Seriously though, I hope most everyone who reads here realizes that while the vast majority of advice available on this forum is sound and straightforward, you still need to use some common sense. :)

One of the primary reasons for a thermostat is to get the engine UP TO operating temperature as fast as possible.... This decreases wear on the engine by having the fit of the important friction internals by having them at their heat expanded size... which it what the engine must be built to run at. Otherwise you have binding... a natural no no of course.

Let us consider the Nitrogen in the tires... We ALL run 78 percent Nitrogen just by using AIR from the ATMOSPHERE in our tires...

To increase that ratio in the tires would require the use of tubes or vacuuming out the tubeless tires... at which point they would be collapsed off their bead .... thus allowing no pressurization.

And this to increase the Nitrogen from 78 to some higher ratio ? Dubious Science at best.

I'm a bit curious about this. Large commercial aircraft tires are typically filled with straight nitrogen, however, I was under the assumption that the nitrogen is used because it has no oxygen and is therefore non-flammable if the tire were to overheat (which can happen on an aircraft).

How does the nitrogen allow the tire to run cooler? Greater heat absorption of nitrogen rather than oxygen? Seems insignificant? :confused:

You cannot have "binding" of parts that are smaller at lower temperatures than they are at operating temperatures. Ever re-machine a connecting rod??? You have to cool them between honing cycles because metal expands, decreasing clearances.

Why do you think a piston skirt will score a cylinder wall when temperatures exceed normal operating levels???

Have you ever seen a piston seize in a bore from running at too low a temperature??? It just doesn't work that way.

100% Nitrogen (again a competition trick used for years) is much, much different than the air we breath.

Yes. Vacuum is applied to the tire/wheel assembly and no, the bead doesn't unseat at 20 in/hg.

This has been used for years in endurance events. Argue the point with CART and NASCAR if you don't agree with the science. The biggest advantage is decreased tire temperatures and improved wear characteristics.

If you don't agree with a practice, you most certainly shouldn't employ it. Its just that simple...Bert

"You cannot have "binding" of parts that are smaller at lower temperatures than they are at operating temperatures."
"Why do you think a piston skirt will score a cylinder wall when temperatures exceed normal operating levels???"

Those are contradictory statements and you make MY arguement with the second... Aluminum expands at about three times the rate of steel.... You can install an aluminum piston that into a steel bore which will move cold... and bind at what should be its working temperatures... You also have the piston subject to different temperatures than the bore.. since its top is subject to the combustion and not as well cooled as the bore with its water surrounding it.

"100% Nitrogen (again a competition trick used for years) is much, much different than the air we breath."
It is different due only to lack of humidity , 1 percent noble gases, and 21 percent oxygen.... how you get the " much much" I don't know.
I do think the physical reactions to heat are not enough to bother with.
My uncle used to use Propane in tractor and trailer tires ( for ease of carrying it around compared to a compressed air tank )... but I would NOT suggest doing that.

Oh, you had just better quit now while you are still behind........... :D

Leathermang,

I don't place much faith in ASE Certifications, although I hold Master's Ratings in Engine Machinist, A6/A8/L1, Suspension/Hydraulic/Air Brakes, Automatic Transmissions/transaxles, including several ACT's from BMW and some MBZ Service Awards I have collected over the years, but the most impressive things to me are those that work in actual practice, not theory.

Much like the bumblebee that is not, from a scientific standpoint, capable of flight, yet defies physics with every flight.

Growing up in a family business afforded me daily access to an Engine & Chassis Dynometer. As the lead machinist, I personally analyzed wear in hundreds of engines over the years and supervised final assembly on many of our more costly projects.

My Father spent a number of years working with Parnelli Jone's successful competition vehicles prior to opening up his own business.

We also built a number of 317 CID Ford Industrial V8's for Wind Machines, that were used in Orange Orchards, for several ranches in and around Central California.

We also performed all the maintenance on these engines and rebuilt them when they needed replacement. We noticed a drastic reduction in cylinder wall wear when we reduced coolant temperatures below 190 degrees F by eliminating the thermostat.

Keep in mind, we were working on these engines and 'tracking' their performance in operational hours. Oil consumption was reduced greatly when temperatures were lowered. Measurebale wear at teardown was also reduced. We saw like results in a 429 Ford in our Tow Vehicle that lugged our Dragster all over California and Nevada to compete in NHRA Division 7 Competition.

The point regarding your theory of 'Cold Binding' of working parts is interesting. Let's examine it based on your reply to this post.

Your average expansion rate of aluminum we will accept, although you failed to mention the different expansion rates of the various alloys, such as the Hypereutectic variants, but we will use your estimation of "3 times the rate of steel" as a baseline.

As the piston is heated, it expands, reducing the clearance bewteen the skirt and the bore. The piston doesn't "shrink" as it is heated, it expands.

As long as operating temperatures are within a given range for the thermal expansion rates of the piston & cylinder, metal to metal contact will not occur.

If you wish to analyze the Caterpillar 3208 V8 Diesel, machine specifications demand that each successive cylinder is bored larger (as you progress rearward) due to their elevated operating temperatures and characteristics of the cooling system, which neccessitate additional clearance to effectively compensate for elevated temperatures in the rear cylinders.

I understand the point you are trying to make, but in hundreds upon hundreds of engines disassembled, measured and reassembled over the years, I have never seen unusual cylinder wall/piston skirt wear from reduced operating temperatures.

I have, however, seen a number of galled piston skirts and scored cylinder walls from overheating.

I have also seen Air Cooled Duetz Diesel Engines (overheat a piston from a plugged fuel injektor) and seize the piston so tight in the bore, it pulled the connecting rod in half.

Think for a moment about residual heat from the combustion process. An internal combustion engine will produce a certain amount of heat, even if you remove the thermostat. Cooler running engines last longer and make more power. This is a fact long proven on the dynometer and why "Low Temperature Thermostats" are populare components of many ECM "Chip" upgrades.

The following post will address your a few things relating to Nitrogen Inflation...Bert

Nitrogen Inflation:
 

Leathermang,

Air is about one-fifth oxygen, and oxygen, especially at high temperatures and pressures, is a very reactive element. In addition, air migrates through rubber. Tires can lose roughly 2 psi per month as a result of air passing through their sidewalls – like a balloon that shrivels up, but much slower.

That’s why regular inflation pressure checks are a must. Even if you don't have a puncture, you can still be losing pressure. Additionally, when oxygen passes through rubber, it can come into contact with steel cords, causing them to rust.

Water vapor in compressed air acts as a catalyst, accelerating rust and corrosion. Water vapor also absorbs and holds heat. And, when it changes from liquid to vapor, water expands tremendously in volume.

This is why tires inflated with air tend to run hotter and fluctuate in pressure more. In competition cars, small changes in tire pressure can adversly affect handling & braking, which is why so many sanctioning bodies require Nitrogen Inflation.

The air around us is full of water vapor as you have pointed out in your response. Compressing air concentrates the water in it and when you compress air, it takes up much less volume, but the percentage of water (by volume) is greatly increased.

While both nitrogen and oxygen can permeate rubber, nitrogen does it much more slowly. It might take six months to lose 2 psi with nitrogen, compared to just a month or so with air. Nnitrogen is far less reactive too. It doesn’t cause rust and corrosion on steel or aluminum, and it doesn’t degrade rubber either.

Alloy wheel surfaces stay smooth and clean, rubber remains supple and resilient. Inflation losses are minimized and reliability is enhanced.

Large trucking companies have begun experimenting with Nitrogen Inflation and a number of technical articles to this effect are available for review.

One test I studied showed increases (in tread/tire casing life) of up to 26 percent. Less rubber aging and tire cord rust could also yield a higher proportion of retreadable casings – and casings that can survive more retread cycles cuts cost per mile too. If trucks/trailers go out and don’t come back for six months or more, being able to keep consistent inflation pressures may greatly lengthen tread life.


That's also better for the environment if you choose such concerns.

Check this site out for some additional information: Nitrogen Inflation

The bottom line is, I want every possible advantage on my cars I can find, even if it is seemingly insignificant to you, I believe in practices whose results I have studied personally and have found them to be worthy of implementation.

Many features on the Mercedes-Benz you drive are the results of countless competition victories, further proving actual practice versus theory alone.

I doubt you drive your cars as hard as I do, nor do I believe you run as much injektor or boost pressure. Under normal conditions, I see no reason why you should alter your car from its original configuration.

In my case, I drive over 108 miles a day (round trip) in +100 degree weather at speeds well in excess of 80 mph when traffic permits. I use speed rated (HR) tires for this reason and I upgrade the braking system with cross-drilled rotors and DOT 5 Silicon Brake Fluid because I seek every small advantge I can find, because it equates to the overall performance of the vehicle as a whole.

Like the US Government, Aviation Firms and the US Postal Service, I have spent 15 years using Silicon Brake Fluid without any of the horror stories you read from people who shake it, contaminate it and/or otherwise install it improperly and then condem the product because of their own inability to follow directions.

I enjoy this debate and you will never convince me I can prolong the life of my engine by increasing coolant, oil and exhaust gas temperatures. I have never seen a 'cold' engine (which will always run between 160 and 180F even without a thermostat) exhibit more wear than one that ran at higher overall temperatures.

This thread has long ago addressed the original issue of thermostat useage and broken bolts, so now it serves simply as a means of discussion, which I think adds greatly to the overall character of this forum. However, just as we must both respect each other on a technical basis, we must also agree to disagree.

With my higher boost pressures, greater volumes of intake air, increased fuel delivery pressures & volume, I prefer to reduce (and maintain) coolant temperatures on my engines because the practice has proven itself time and time again.

Of course, this practice isn't for everyone and not everyone has access to the testing facilities I have been priviledged too that allowed me to test these theories prior to their usage.

Additionally, manufacturers will always tell you not to modify the car from its original specifications since they have no control over the skill level of the enthusiast and a general concern over product liability and warranty considerations.

However, when properly configured, a number of small changes to a vehicle's overall operating efficiency can yield significant benefits.

I will guarantee my 7.4 Litre Pontiac produces much more power than the 6.6 Litre engine it replaced, even though I modified it extensively from its original form, including removal of the thermostat.

There is also significant evidence that 100% glycol (water free) cooling systems offer great benefit over conventional water based coolants, both in competition and for fleet useage. Quite possibly the greatest benefit is zero cooling system pressure and higher controlled temperatures without boiling.

Refer to this website for details:
Water-Pressure Free Cooling Systems:

I enjoy your input and I hope this thread proves interesting, as well as informative.

Best of luck on your projects...Bert

I want to restate for the record that I think a thermostat is primarily for WARMING up an engine as fast as possible... as compared to being an impediment to cooling... as the elimination of yours tends to imply...

Manufacturers make engines to run at a particular temperature.... You are probably too young to remember when manufacturers changed from typically 180 degree to 195 degree thermostats.

I am just in this debate to make sure potential newbys to automotive DIY keep in mind that your focus is on race engines... even if you monitor your engine wear and such... you are in a forum where people are proud of cars which are Decades old and into multiple 100,000 mile odometer readings... A car like that is going to do a lot more heating and cooling cycles than any race engine... so the potential ( if I am correct about the purpose of the thermostats ) for wear in that time from cold to working temperature is Greatly Magnified.

As for the tires and oxygen... a new report says not to keep tires over 6 years.... but for the record I think there are several factors like rubber composition, asphalt type and temperature which would affect the situation before taking out that 21 percent oxygen from inside your tires would show up. Of course tires should be checked for pressure ( only when cold ) on a regular basis. It also sounds like you need a water seperator in your air supply ...As to your " tires tend to run hotter".... this is usually a good thing due to the reason you pointed out about them losing air slowly... the Primary cause of excess heat build up is from low inflation causing sidewall flex. So the implication that the air expands more most of the time is a plus for normal drivers and situations.

That you drive your cars harder than I do is the understatment of the decade. I only have 67 hp on a Good Day....

Why did you not reduce the temp below 190 BY Using a lower temp thermostat ?

Bert,

The post on the lack of use of a thermostat is very enlightening and I enjoyed reading it.

I tend to agree with the majority of the information presented with two exceptions/comments:

1) The use of no thermostat can seriously impede the warmup of the engine up to the typical operating temperature of 150-160F. The wear during a cold start, especially a cold start from 20°F, would be significantly more. This would lend credence to utilizing a 150°F. thermostat. The thermostat would be wide open for the entire time, after the warmup has been achieved.

2) The hotter you can run an engine, the better the fuel economy. A cooler running engine absorbs more of the heat produced by the engine and less of the heat is available for doing useful work. When I worked for Chrysler, they had setup a specially designed 225 slant 6 to run at 235°F. A 235°F thermostat and a 20 lb. cooling system with 100% glycol IIRC. The vehicle achieved some phenomenal fuel economy numbers. Something like 20% better than the same engine running at 195°F. The vehicle was never produced, however, presumably because of durability issues. I would guess that the engine suffered increased cylinder and ring wear at those elevated temperatures.

Just a couple of things to ponder.

That's primarily what I was thinking - the Carnot efficiency comes to mind. And the heating system for the passengers works better too. I can enjoy the sunroof on many a winter day provided the heater is running hard. As for the slant 6, they must have run that puppy long and hard to get a lot of wear. That was one of the most durable engines ever made. I had a 74 Dart in college. My buddies borrowed it for a 800 mile road trip, most of the way with the oil light on. Had a pint left when they got back :eek: didn't seem to bother the car either.

Leathermang,

I do remember the switch to 190 thermostats and even the .080" plug gaps on the older GM models. I'm only 40, but I have spent a lifetime around automobiles. Most of it was in the high-performance field working with 'street rod' style projects in the family business.

In this arena, very small changes in a vehicle's performance is desireable, something that would seem moot to the average hobbyist. You are also correct in your concern to keep the focus in perspective for the DIY audience and I appreciate your concerns in that respect.

I think my geographical climate has a lot to do with how we set up engines, since it is hotter more often than it is cold here. Lower temperatures allowed more ignition advance, which made the car stronger off the line and/or out of the corner.

In fact, one of my teams most successful cars was a 1966 Ford Fairlaine with the 427 'FE' engine. This was an 11.5:1 compression engine with dual 600cfm Holleys in factory trim.

I discovered the engine pulled very hard off the line when we advanced the ignition timing from 10° BTDC to 15° BTDC, but our MPH fell off, since the advance worked against us at higher rpm.

Since this engine gave its best top-end performance at 34° BTDC total timing, I had to rework the distributor to give me the 15° of initial advance I needed, yet hold my total timing to 34° overall.

To give you an idea of how sensitive this engine was to heat, I discovered it had a slight tendency to 'ping' when the clutch was released at 5000 rpm against very sticky slicks. Changing the spark plug heat range from #5 to #2 eliminated this 'ping ping ping' when the clutch was released. And this was with Sunoco 130 Octane Racing Fuel, which was leaded back in 1986.

To make a long story short, I wired the dual point distributor to run on one set of points and then activated the second set in 4th gear to effect a high-speed timing retard of approximately 6° overall.

The result was a car that left the line very hard, pulled well through the gears, then really came on strong as the ignition was retarded slightly in high gear under heavy loads. RPM through the timing lights was between 7200 and 7400.

The lower temperatures worked equally well on our tow vehicle, so I began to implement it on my street-driven cars with positive results. More advance, better vacuum and throttle response were the key factors I cited for doing this modification. The biggest reason for elimination of the thermostat is mechanical reliability.

On the Diesel, I prefer the lower underhood, oil and coolant temperatures afforded by the open 'restrictor' orifice in place of the thermostat, especially with elevated boost and fuel pressures.

I even go as far as blocking the exhaust heat crossover on the Pontiac to lower intake charge temperature, much in the same way an intercooler functions.

Not something you will need on a 240D.

Brian,

Your work with Chrysler is impressive and those early studies you mention are why the modern manufacturers are running engines hotter. Fuel economy is always better with elevated temperatures.

I saw an article recently where an engine was modified to run with 'preheated' gasoline. Apparently, the vapor was more concentrated in this fashion and yielded more heat energy.

I would like to hear more about some of those early studies...Bert

Regarding Nitrogen..........

From Modern Tire Dealer
http://www.mtdealer.com/t_inside.cfm?action=art_det&storyID=1207

Stephen

Actually, I do see the point about using nitrogen to inflate tires. But on a practical note, where do you draw the line? It's sort of like spending a few bucks on premium wax and applying a few hours of elbow grease so maybe you can reduce the drag coefficient by 0.1%. Then there articles like the one above that start out with reasons like this: 1. It has more mass, so it migrates through the tire three to four times slower. The result: Tires hold their psi longer. Anyone who passed high school chemistry knows that nitrogen has an atomic weight of 14 and oxygen has 16. nitrogen has less mass, not more. Other statements in this article may very well be true, but I stopped reading near the beginning.
Does it prolong tire life a little bit? Maybe, but I'm not paying anyone to fill my tires with nitrogen just yet.

Personally, I go out of my way for even a slight performance advantage and to me, this is accepatble. I always have Nitrogen on hand because we have used it for so many years. I rent a bottle for $3.00/month through the shop.

Getting back to what Leathermang was saying about wear while the engine is cold...I have never seen any evidence to support this claim, so I am somewhat puzzled on the theory behind it.

Let's take the 317 Cubic Inch Ford Industrial V8 used in Staionary Pumps and Wind Machines.

We accepted a rather large account to rebuild these engines for a large citrus grower. We tracked the engines and service was performed at our direction.

After a pre-determined number of hours, the engines came in for service.

When we started the account, the engines all had 195° thermostats in them and cylinder bores were very worn, as were the valve guides.

After reboring and fitting new pistons, we reinstalled the engines, without thermostats and tracked them the same number of hours they had been running them before.

The difference was unreal. Cylinder wear was around 0.0025" taper where before the engines measured well over 0.0080" and needed to be sleeved or bore to the next oversize.

Valve guide wear was also noticeably reduced.

This was not just one engine, but dozens of them, including the 429 in our tow vehicle which pulled a race car all over the state.

Any studies you are aware of addressing/supporting your theory would be welcome reading for me.

Thanks...Bert

Bert, I have no evidence to support the theory, however, my general opinion is that oil which cannot flow very well will not provide the film necessary to prevent metal to metal contact.

Whether this is true, and at what temperature it becomes true, is the question.

After viewing dino oil at near 0°F., I can picture that it has a difficult time to properly coat the cylinder walls and bearing journals until it warms up a bit. Now, it does not need to warm to 100°F., that is for sure. But, at very cold temperatures, I do honestly believe (without any hard evidence) that there is more wear.

Of course, this would not be evident in a typical climate of California. Another reason that running without a thermostat would not be an issue.

Some things have to be from inference... not all information is available on the web..

What is the lowest temperature thermostat you have ever seen a manufacturer suggest for their water cooled engines ?

What is the highest ?

That range is not very large in my case.... perhaps 175 to 195. Why is there such a narrow range ? For those manufacturers which choose a thermostat on the high side.... what factors do you think they ' missed' when you choose to go to the other end of the scale ?

Remember that on our vehicles we are not talking about short lived bores... on the contrary... we are talking about engines famous for long life if normal maintenance is followed.

Here are some interesting url's.... notice how focused they are on expansion rates and piston fit.

Much of our engines desired thermal characteristics are SET AT THE FACTORY... because they choose the type material used for the pistons, the design of the pistons and the material used for the bore.

Several of these sites talk about increased wear happening at that point before the expansion has brought the parts to proper fit.

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http://courses.washington.edu/engr100/All_Sections/Engine/UofWindsorManual/Piston%20Design.htm

" The piston is designed to be an elliptical shape when cold. As the engine reaches operating temperature, the piston pin bore area expands more than other thinner areas of the piston. At operating temperature, the piston shape becomes a circular shape, which matches the cylinder bore for improved sealing and combustion efficiency. "

http://www.diy-boat.com/Pages/Archives/links/eng983.html

http://piled-arms.com/tech38.html

http://abbysenior.com/mechanics/short.htm

"The skirt is the only area of the piston which contacts the cylinder walls. The clearance between the piston skirt, and the cylinder walls must be very precise, and depends on the type of pistons used in the engine. Aluminum and iron have different expansion rates. Aluminum, because it is not a very dense metal, takes on heat very easily, and gives it away again very easily. Iron, on the other hand, is very slow to heat up, and remains hot for a long time. If piston expansion was not controlled somehow, the piston skirt would grow to be larger than the cylinder its' going up and down in, and obviously, the engine would seize up. Cast pistons, because their expansion is controlled with a band of steel. can have a relatively small piston to wall clearance of .003"-.004". These bands are placed in the piston mold before the molten aluminum is poured in, and are around the wrist pin. This makes piston expansion parallel to the wrist pin only. The piston skirt is then ground to be oval shaped, or "Cam Ground", so there is the same clearance between the skirt and wall when the engine is hot, as when it is cold. There is, however, more area when the engine is hot. Pressure, and therefore wear is much greater when the engine is cold, but the engine is still quiet, with no piston slap."

and I just thought this next one was interesting.....

http://kb-silvolite.com/index2.php

from
http://www.beckracing.com/page05.htm

" Piston to Bore Clearance for KB Performance Pistons were dyno tested at wide open throttle with .0015", .0020", .0035" and .0045" piston-to-bore clearance. After 7-1/2 hours, the pistons were examined and all looked as new, except the tops had normal deposit color. Even with 320 degrees oil temperature, the inside of the piston remained shiny and completely clean. Excess clearance has been shown to be safe with KB pistons (no reported cracks in four years). The added skirt stiffness of the KB pistons reduces piston rock, even if it is set up loose. Loose KB pistons over .0020" do make noise. As they get up to temperature they still make noise because they have very restricted expansion rate and do not swell up in the bore. Our hypereutectic alloy not only expands 15% less, it insulates the skirts from combustion chamber heat. A short term Hp improvement can be had by running additional piston clearance because friction is reduced. To obtain actual piston diameter, measure the piston from skirt to skirt level with the balance pad. See The Special Clearance Requirements for KB Pistons.

Pin Oiling should be done at pin installation. Either pressed or full floating, prelube the piston pin hole with oil or liquid prelube, never use a grease (if you are using a pressed pin rod be sure to discard the spiral pin retainers). All KB Performance Piston sets supplied from the factory include a tube of Torco/MPZ engine assembly lube. A smooth honed pin bore surface with a reliable oil supply is necessary to control piston expansion. A dry pin bore will add heat to the piston rather than remove heat. Pistons are designed to run with a hot top surface, and cool skirts and pin bores. High temperature at the pin bore will quickly cause a piston to grow to the point of seizure in the cylinder.

Marine Applications generally require an extra .001"-.003" clearance because of the possible combination of high load operation and cold water to the block. A cold block with hot pistons is what dictates the need for extra marine clearance see our clearance chart on The Special Clearance Requirements for KB Pistons."

http://www.canadiandriver.com/articles/jk/020320.htm

http://64.78.42.182/sweethaven/MechTech/Automotive01/default.asp?unNum=2&lesNum=3&modNum=1

http://www.dkw.co.za/Cerametallic_Coatings.html

http://www.babcox.com/editorial/ar/eb40354.htm

Interesting reading Leathermang...

I use the KB Hypereutectic Pistons in a number of engines with very tight bore clearances (.002") and ring gaps of .014" top and .016" second. Good quality products right out of the box, although I opt to have my skirts teflon coated before delievery.

One thing I have noticed is almost all liquid cooled engines will run at 150° to 160°F even without a thermostat. The interesting part is how fast the engines come up to that temperature.

On my 7.4 Litre Pontiac, the heater is 'warm' in less than 1 minute and the engine is up to 160° in less than 5 minutes.

On a 104° day here in California, sitting in the drive-through at In-N-Out for 25 minutes with the A/C on, the coolant temperature will never go past 185°F. That is with the stock 4 row copper/brass radiator, 60/40 water/coolant ratio and stock engine driven 7 blade fan.

At 104°F ambient temperature at 70mph with A/C on, coolant temperatures stay right at 165° to 170° and steady.

My theory has always been that with the 'hollowed out' thermostat body in place, functioning as a restrictor, the coolant flow would be identical to the flow available when the thermostat was fully open.

No I certainly agree with you about the 'cold oil' theory, but in reality, the oil heats up quick in an engine, must faster than the coolant seems to.

Much like 'piston slap' that we used to experience with Forged Aluminum Pistons and very loose clearances (.007") cold, would go away after about 30 seconds because the pistons heat so quickly.

Interesting...Bert

The ' cold oil ' theory is more Brian's ...... Mine is the ' oval cut pistons made from aluminum are designed to run at a temperature already figured out by million dollar R and D departments ( and warranteed engines returned to them if necessary ) so that the expansion fits the bore correctly ( and particularly close on our Diesels ) during running.

You are correct, Leathermang and those pistons are likely up to temperature within a minute of exposure to combustion heat.

With the old TRW 'Powerforged' Racing Pistons, you had to run them really loose, about .007" clearance cold and they would 'slap' until they warmed up. It was a very hollow, distinct sound.

The pistons picked up enough heat to quiet down after 30-45 seconds of running...Bert