Another Thermostat Adventure

[MT_Wessels]

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.

Regards
Wessels

[Pete Burton]

Originally Posted by MT_Wessels

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. This is exactly where it should be - did you think this was overheating? 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?Leave it be, it's a switch that prevents the heater blower from running until the coolant temperature has reached a certain level, about 52C IIRC- 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. Who cares what your neighbor thinks. Learn some more about your nice car, fix it and drive it. If that doesn't pan out, sell it here

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

Regards
Wessels

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

[Pete Burton]

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.

[tenknots]

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.

[MT_Wessels]

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?

[FarmerDrew]

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.

[SD Blue]

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.

[Doktor Bert]

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....

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

[Dervman]

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.

[MT_Wessels]

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.

[Pete Burton]

Originally Posted by Doktor Bert

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....

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

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!

[MT_Wessels]

Thanks Pete
I am finally seeing the light
"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.

[leathermang]

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.

[Doktor Bert]

Originally Posted by Pete Burton

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!

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

[Doktor 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