I’m going completely insane over this. This is regarding my (new/old) 84 300D with almost 200,000 miles on her. This car has run warm consistently since I bought it 5 weeks ago. But now it is running even hotter.

When I buy a car, one of the first things I do is a thorough cooling system flush and then I replace all the hoses and water pump, which I did. (I believe in preventative overkill, to a certain extent). The system was already clean, as the flush water was not very discolored at all. I used an OEM type water pump (Meyle – is this an actual OEM supplier?)

The radiator was original, and Last Friday it succumbed to the “neck crack” syndrome. Luckily, I caught it immediately, so I didn’t fry the engine. It *did not* overheat. I replaced the radiator with a new Behr OEM type unit. The first replacement thermostat (Wahler) was defective, and I replaced it with a new dealer supplied OE one. It is positioned correctly, with the arrow pointing up. I filled her up with a 40/60 mix of phosphate free antifreeze + Water Wetter. The auxiliary fan functions properly. The viscous fan clutch is O.K. The metal bypass line is clear. There is no air trapped in the cylinder head, since it is self-venting.

The temperature gauge is reading accurately, confirmed multiple times with an infrared non-contact thermometer used on the engine block & cylinder head. The new (2nd) thermostat was checked in a pot of water, and it starts opening at 180 degrees.

After all this, the engine runs at 97- 99 degrees on the gauge, no matter what the load – light load, medium load, A/C on, A/C off, 60 degrees ambient, 90 degrees ambient, etc. You get the picture. Can you spell F-R-U-S-T-R-A-T-I-O-N? I guess that I should be satisfied that it is at least *stable* at 97-99 degrees, but I am ready to try a THIRD thermostat. I can’t think of anything else.

<< UPDATE Since I first wrote this: Today I ran the car on the freeway in hot weather with the A/C on, and also in traffic, and the temp went up to 103-105. >>

IF the head gasket were leaking into the cooling system, I don’t believe that the cooling system would retain pressure in it overnight, which it does. Unless there is such a phenomena as a one-way leak (?!).

To reiterate: The system was flushed thoroughly. I now have a new radiator, new hoses, new OEM pump, new thermostat(s), proper coolant, a functioning visco clutch, a functioning auxiliary fan, a clear bypass line, and this thing still runs HOT. I am at my wits end. Plus, there is a terrible feeling of deja-vu happening here – when I first discovered MercedesShop.com, I was having cooling system problems with another car, hence my chosen name: RunningTooHot.

Anyways, I hope that someone can point me in a direction that perhaps I’ve overlooked. I like to delude myself into thinking that I’m a fairly competent DIY’er, but this is making me feel like a moron.

Thanks in advance for any suggestions (other than selling the car, thank you :) )

RTH

. . . pretty thorough so far
 

I can understand your frustration but 100C is only 212F, so that's not too hot at all!

Maybe try to turn the aux fan(s) on a little sooner with an external resistor, and that should lower it to around 95C or so.

No water? Maybe that's the reason...

I may catch some flack from saying this but I would try running it without a thermostat and see what happens. Also, try 100% water. I have seen holes drilled in the outer plate of thermostats to help cooling issues. I would only do this for testing purposes and would not consider it a long term fix (especially the 100% water idea) unless removal of the thermostat makes it run "normal".

Water could be one factot as pointed out above.

The other one - is to see if the fan actually kicks in when the temp heats up. It could boil down to a simple fuse.

At highway speeds the fan should have no effect on cooling since the "ram air" due to the vehicles speed is sufficient unless the airflow across/through the radiator is obstructed. So I wouldn't pursue that. I lived in Dallas for a while and it was not uncommon for the car to run at 105 C and hotter in traffic in the summer.
I'm not familier with diesels except in principle, but if a gas engine runs too lean it will run very hot; is this true also for a diesel???????

Does this car have an auxiliary water pump?

It's the aftermarket water pump. Go get a reman pump from the dealer - last I checked it was priced at $25. Compare the impellers between the MB pump and the one you got. I bet there's a dramatic difference. The factory pump has a cast impeller with very tight clearances to the water pump housing. After market pumps I've seen use a smaller cast impeller, sometimes with fewer vanes. The really bad ones use a stamped sheet metal impeller. These are guaranteed to add 10C to your coolant temperature :)

With a little practice you can get the water pump out of an old 300D in 20 minutes...

It's normal for coolant temperature to run as high as 100C if you're working the car hard on the highway, a/c blasting, and hot weather. However, it should stay near 90C in gentle stop & go traffic.

Thank you everyone for the help!
 

Thank you everyone for the help! I greatly appreciate it! I’ll address each one of your replies individually, in the order received.

JimF: I know that the later model cars such as the ones you own run hotter, and 100 doesn’t seem out of line, but it is not normal on a diesel of this vintage. I actually did turn on the fan manually *just* to see what would happen, although I knew in advance that this was going to be futile. It was.


Rainmaker: Please. I recognize in retrospect that my grammar was incorrect, but then again I was not an English major :) . My writing “I filled her up with a 40/60 mix of phosphate free antifreeze + Water Wetter” meant that it was a 40% anti-freeze / 60% water mixture PLUS Water Wetter. Seeing that the cost of Water Wetter would work out to about $75 per gallon, this form of ignorance would have been not only just plain stupid, but very expensive as well. I guess that *everything* needs to be ruled out though….


Engatwork: The way that these systems are engineered is such that the thermostat does not work in the typical manner. It functions to open the passageway to the radiator as well as acts to close off the bypass circuit at the same time. Running this type system without a thermostat will not cause ALL the coolant to go through the radiator with each circulation, whereas on (most) other cars it would.


Ymsin: Oh how I wished that were the case. But much to my surprise, I discovered that on this car there is NO thermo switch sensing the coolant temperature for fan activation. Really. It is in the wiring diagram. It kind of blew my mind, but then again, that seems easy to do lately :) . The auxiliary fan is switched on ONLY via the temp sensor at the A/C receiver-dryer. And it does work – the fan comes on with the AC.


Intruder: Absolutely correct about the ram air effect. But, there is no blockage to my radiator. My gas engine cars behave exactly as you describe. The diesel should not be this hot under light loads & low ambient temperatures. Diesels run lean inherently, but that is another thread altogether. It does not make them run hot in the same manner as a gasoline engine.


Yal: Yes it does have an auxiliary water pump. It’s primary purpose is not for engine cooling however. It circulates water to the heater core.


Jcyuhn: I saw the 'Pep-Boys special' water pump with the stamped sheet metal vanes. I passed on that! I can only imagine the problems with cavitation that pump would cause, although American cars have used that type since the dawn of time itself. The pump I put in does have the cast impeller, but I did not actually measure the diameter. I am desperate enough that I am going to go get a dealer supplied pump & try it out. Too bad I ***** canned my old original pump with the official star on it – the core charge is $67! Maybe Mercedes prices it’s pumps so low to act as a sort of “education” for us DIY types. In other words, “Come to us for parts, they’re not *that* expensive, and if you already tried an inferior product, we’ll bend you over a barrel for not having OUR core!” (Just a conspiracy theory for those paranoid types, as well a for entertainment purposes.) ;)

If anyone else out there wants to take a stab at this, *Please* do!

THANKS AGAIN EVERYONE!
RTH

thanks RTH for the heads up as to the circulation operation. Another thought did come to mind too. One day while driving with the temp up to the 100 mark turn the defroast on full blast and watch the water temp gauge. I can make the one in the E320 drop at least 10 dC by doing this. Believe me, I don't leave it on long. Anyway, it is my opinion, that if you can't make it move doing this there is a problem with the sensor/gauge system.

Well everyone, I bought a Genuine Mercedes Benz water pump today from the local dealer (sorry Fast Lane – as quick as you are, I wanted it NOW, plus you don’t have the OE pumps.)

Call me anal, but I had to determine the differences between the two pumps. The impeller diameter is the same. The design of the impeller is *almost* the same, except for a more squared off 45 degree edge to the ends of the blades on the Meyle. The blades themselves are MUCH thicker compared to the OE pump. Then again, the rebuilt OE pump may have a lot of material missing from the impeller compared to when it was first cast. Another seemingly critical (and probably MAIN) difference is that the end of the impeller (not the shaft itself) is about 2-3 mm shorter on the Meyle pump. This will equate to an increased gap between the pump impeller & the rear of the pump housing which will decrease its efficiency. 1/10th of an inch may not sound like much, but we’ll soon see. Stay tuned…. I’m going to go button it up now.

And Engatwork, I tried the heater method of cooling her down, and it did not make much of a difference, at least not as much as if should. It went down a bit & jumped right back up again. The sensor & gauge system is working perfectly, substantiated by using the infrared thermometer. (A nice little addition to the tool box, if I may say.)

IF this doesn’t work, I’m going to throw in the towel on this. I hate to admit defeat, but if this car wants to do an impersonation of Chernobyl, so be it. I just hope it doesn’t melt down when I’m on an extended trip.

Thanks again everyone!
RTH

Here are some more longshots to add to your bag of worms; sorry in advance. The transmission is a possible cause by putting more load on the engine (thus higher temp) than usual. The pressure pumps inside the tranny can put excessive loads on the torque converter which the engine must overcome. It's a long shot.

The same can hold true for any of the accessory items, especially the a/c compressor. But, if you've ruled out the radiator, the water pump, airflow blockage and water passage obstructions I think you might want to consider these.

Another one is an obstructed exhaust but you probably would notice the change in sound and the loss of power.

It's all I can think of.

I was desperately grasping at straws, and to no avail. The OE pump did not change a thing. I am completely stupefied by this car.

All I can hope for is that one of the ‘Super Techs’ here can pipe in on this exasperating situation. There is no substitute for experience. Someone that has witnessed the idiosyncrasies of dozens or even hundreds of these cars may have an idea. Perhaps one of their customers has had a similar problem; perhaps it is an early sign of greater problems yet to come, such as a head gasket in the early stages of failure? I don’t know.

Additional information: This does not seem to be a problem with cooling capacity per se. For example, when the gauge was reading about 98, I checked the temperature of the *hot* side of the thermostat housing, the infrared thermometer read 99 degrees. The (cooled) water return pipe going from the bottom of the radiator to the thermostat housing reads between 60-65 degrees; so the radiator is cooling the coolant. This would seem to indicate that the thermostat is not opening properly, but I’ve now had THREE different thermostats in the car. What are the odds of 3 bad thermostats in a row? Rather astronomical. If only I had such ‘luck’ with those odds consistently, I’d play the lottery!

Thanks Again Everyone!
RTH

RTH:

I'm certainly no pro, but am curious about this situation.

You mentioned replacing the radiator with a Behr OEM.

Is there any possibility that the capacity or the flow characteristics of this unit are different than it's predecessor? Just a thought.

This is a stab in the dark, but here goes. Does the intake manifold look like it has ever been off? Can you see RTV silicon or the likes around the edges. It could be quite possible that the flow could be restricted due to carelessness with the use of such products. I had a 72 vette that I had to go back and "clean up".

Good luck,

Steve

Hi RTH:

I don't know if your car has a catalytic converter or not but if you do, you might want to check that to see if it is clogged.

Aloha,
Eric

A couple of ideas: check condition of water hose on suction side of water pump. perhaps it is collapsing when the car is running, but appears ok when you look at it; are you certain you are actually getting all the air out of the system? The dealer had a heck of a time getting all the air out of my w124 after a radiator waterpump replacement under warranty. The car ran warmer than usual but not hot until they got it out. They had to raise the front of the car on rampstands and warm it up, then turn the heater to full hot.
One would think that this wouldn't be necessary, but it was.
Also, maybe I read too fast, but where are you? In Fort Worth it is 102deg right now and there is no way my car is going to run at its "normal" operating temp.
As far as the hose idea goes I may be all wet since I don't know the config of the 300 cooling system.
Let us know what happens
Steve

RTH,
I looked in Glenns 'Mercedes-Benz Repair and Tune Up Guide'
for additional ideas that have not been posted yet, and he came up with a couple. For overheating:
1. Fan belt slipping
2. Rust and scale in cooling system
3. Exhaust leak into cooling system
You stated that you flushed the system, but the water jackets may be clogged in the engine.
A pump-type pressure test on the cooling system will detect a exhaust leak by fluctuating dial at about 7psi.
Also check to see what is between your condenser and the radiator. On an Isuzu diesel I owned I found a piece of cardboard had been put in for severe cold operation.
Good luck
Steve

First, I want to thank everyone for their input on this matter. I really do appreciate it, plus all of these suggestions will serve as a guide for other people in the future when they search the archives.

Mike Murrel: the radiator is the EXACT same as those from the dealer with one exception - there is no ‘Star’ on the upper tank. Behr makes these radiators for MBZ. Oops, make that two differences, the price premium for the ‘Star’ isn’t included on the Behr OEM unit. Good try though.

Smalltime: Nope. I’ve seen that before myself. Why do people use sealants as though they need a bead the size of that which they squeeze out of their toothpaste tube? Unbelievable isn’t it? BTW, this engine is a virgin. But then again, they all say that. :)

Etsa: There is no converter or trap oxidizer on this model.

Steve Hutson: The hoses are brand new & O.K. Plus the pressure in the system tends to ‘balloon’ them out which further keeps it from collapsing. You are quite correct as to the ambient temperature: it is about 90 here today, and I don’t expect the car to run really cool, but the temps I described occur even at ambient temps in the 60s. There is no rust or scale in the system, nothing between the condenser & the radiator, and the belts are also new & not slipping. As far as the exhaust leaking into the system, that seems to be the only thing left that I can think of. However, if the head gasket were bad, I would have other symptoms such as *high* pressure in the cooling system which would then blow out through the pressure cap. Plus I am not loosing any coolant, and the system holds pressure in it overnight.

I REALLY wish that someone like Stevebfl would chime in on this thread.

THANKS EVERYONE!
RTH

Really hard to get involved with seamingly such a straight forward problem. The answer is often in some assumption associated with casual observation.

Does the aux fan turn the right direction? Seen it twice that the polarity was reversed.

After being proded I read all the good suggestions and have been waiting for the results of the new pump. The depth and design of impellers are very critical and I don't think MB reuses the impellers on their rebuilts.

You are within ten degrees or so of normal operation, could your gauge be off.

Timing does make a difference with diesels. I hate to send you on a wild goose chase but timing would also include cam timing. Retarded cam timing will overheat a diesel quickly.

Anything that reduces power will increase heat. Do you get good boost? The car should be running at a few pounds of boost at constant speed above 50mph. Check the boost at the aneroid because lack of the signal here causes reduced fuel and less performance. You should have 9-10psi boost at full throttle.

Steve,

I know that it is hard to make a judgement from afar, but I am wondering if this is how they behave when the head gasket *first* starts to go bad. That’s the only thing that I can think of other than the IP timing. I know that assumption is the kiss of death, but I WAS assuming that the pump timing is OK because the cam timing is Perfect – I checked (visually, not with gauges) when I did the valve adjustment about 1 month ago (When I first bought this car). But having said that, I will check to see if it has drifted (or IF the timing chain was replaced at some time, & perhaps the pump timing was incorrectly set).

Fan polarity is correct. The new MBZ pump made NO difference at all. In fact I saw 107-108 on the gauge today, although it was 95 degrees outside today. The temp gauge is Right-On-The-Money. Checked & verified by using an infrared non-contact thermometer on the engine right where the temp sender is located. I am getting boost at the aneroid, and my car peaks at a little over 600 mbar. I haven’t adjusted the wastegate yet, until I get the heat problem under control. (Plus I have a Garret turbo – major pain to adjust. I am thinking about an external pressure regulator instead.) There is constant (low) boost at cruising speeds of 40-50 mph & up.

By the way, I think that MBZ does reuse the impellers, as the one I got does not look like a new casting.

If there is anything else, please let me know. I will try to check the IP timing this weekend, but unfortunately, now *I* am running too hot – coming down with a nasty cold. :(

A debt of gratitude to you Steve!

RTH

Running too hot
 

Runningtoohot,
When you first said you installed a new Behr radiator, Iwas going to suggest you shut the engine off after a long test drive,and check the entire surface of the radiator with your hand to see if it was equally uncomfortable to touch. I have gotten bad Behr radiators,but you dispelled that thought with the non contact infrared tester. I caution you to bear in mind that the field increases with distance. The only way to get accurate readings with that unit is to be within about 4 inches.The red dot you see is only a laser pointer:the unit actually operates on infrared. I now have to agree with Stevehutson:you need to add more water.I had a simmular experience recently with a 300SD.I had to keep adding water even though the expansion tank appeared full. Good luck.

RTH,
The cooling systems on the 5 cyl diesel does not bleed itself out that well. When I fill a cooling system on one of these engines I remove one of the coolant sensors on top of the thermostat housing and pour the coolant mix in (the reservoir) until I have coolant coming out of the hole. You will be amazed at how much the coolant temp will be affected because of an air pocket in the system.

Also if my memory serves me correct the single pole coolant sensor on the thermostat housing is in fact the 212F switch for the aux fan.

HTH

Autozen: could you please tell me more about the “bad” radiators that you have gotten from Behr in the past? What was wrong with them? (This won’t matter in my case, because the radiator is functioning properly, but I’m curious.) I am aware of the distance/field of view aspects of the infrared thermometer. This one has a distance to spot ratio of 8:1, and I *do* use it close up. There is also parallax error to deal with if the laser is used for aiming.

As far as adding more water? I’m not sure what you mean – the system is full. If you are referring to the antifreeze/water ratio, it is 40% antifreeze and 60% water, so I am not going to dilute if further. Perhaps you can elaborate further on your 300SD example. Why would you need to keep adding water unless you were losing it somehow?


Chowpit: When I fill the system, I use the upper radiator hose – I disconnect the radiator end of it and fill up the block & head this way. It is the same thing – it is the high point in the system. I can see on the service CD that the earlier diesels had a different configuration. Plus, this later system is supposed to be self-venting.

The thermo switch in the top does NOT control the auxiliary fan on this model (1984 300D California version). I know that every other MBZ I have (and had) did have a 212 switch where you mentioned. The 1979 240D wiring diagram that I just looked at has a 212 switch also. I don’t know what they were thinking at the factory when they decided to eliminate this from the system.

Thanks Guys

RTH

I think I have read that in the summer it is better to use less antifreeze? I am not sure on this, but I thought that water cooled better than antifreeze. Isn't antifreeze really only needed in more quantity for cold weather situations?

It sounds to me like you have been very thourough.

I would do some research on the mixure ratio and cooling properties of water vs antifreeze. And see if you need to change your ratio or try the chaging of the ratio.

I have a friend who I think uses water wetter and water only no anti freeze and he's in Florida. I'm not sure though.

Alon

RunningTooHot,

I hadn't thought about parallax.If yur're hitting everything:if you're within 5 inches you could be off by 2 inches.Neat tool.Just needs developing.I also have a MAC digital pyrometer,and with the surface,I never seem to get the same reading twice.
I've had a few Behr radiators in the past that acted just like a clogged radiator and had to be changed out again. In general I can't complain about Behr quality, but it is frustrating when you can't win the lottery, and yet you can draw the one bad radiator out of a million.
When I said add I meant liquid in whatever proportion you want.This 81 300SD I changed the pump and thermo on ran over a 100*C after the work.I raced the engine for the longest time with the heater on and drove the car several miles.It's not like the 300D is new to me:I've been putting water pumps on them by the scores since they first came out in 1975.In this case for some reason I started adding water to the overflow tank slowly even though it was full.It kept taking more water (about a gallon Iguess)until it was finally really full.Can't explain it.Wierd air pocket somewhere.

Ashman: you are correct in the aspects of antifreeze being a less efficient of conductor of heat as compared to water. However, like many things in life, a compromise is required. Your friend is asking for trouble, especially if he has any aluminum components such as the head, block, radiator, thermostat housings, etc. Water is known as ‘the universal solvent’. Just because we drink it, it does not mean that it is benign to other things, such as metals. Your friend is going to have a corrosion problem unless he adds something else to the water to prevent it. And before anyone pipes in here, yes, Water Wetter has some anticorrosion properties, but I do not think/believe that it is enough for street use (with water only).

Autozen: I am getting way off subject here, but some of the newer infrared thermometers have a multiple laser setup which displays a ring around the area being read. And yes, it is a really handy tool for numerous things. Thanks for the additional info on the 300SD. I *wish* that was the problem with mine, but its not :(

Thanks Again Guys!
RTH

Damn! I hate when I'm wrong.

When you flushed the cooling system, what type of cleaner/chemical flush did you use? MB recommends a citric acid based flush.

Assuming the engine internals are reasonably clean, I vote for looking into cam/injection pump timing. Can't make any specific recommendations here; I;m out of my experience.

Running Hot
 

1984 300d Turbo 135k
Air In System Remove The Top Radiator Hose Fill With Water

As a damn good M/B tech, I think you have a combustion leak into the system. Maybe head gasket, maybe cracked head. I would monitor the cooling system pressure closely. Release the pressure off of a hot engine and hook up a gauge to it. Rev the snot out of it for a bit (2000 to 4000 RPM) and observe if the pressure rises. A hot engine wouldn't have much thermal expansion so a rise in pressure on a hot engine indicate a combustion leak. That means the head comes off. :(

This thread is from 2001. It was a cracked head as I recall.

I went through all of this and replaced everything (raditor, temp sensor, water pump, fan clutch) and still the temp would go up over 100c. Than I ran into a mb tech on the golf course and he had me check the wiring from temp sensor to the cluster. I soldered a new end on the temp sensor AND ran a new ground from the cluster (back of temp guage) to the body. Now the car runs at constant 90 t 95c and I live in south florida. The ground was the last thing that I did and that solved the problem.

Overheat Engine
 

1984 300d Turbo 135k
Take The Top Radaitor Hose Off Fill To Top, You Have Air In The System Had The Same After I Change My Radiator And Replace Or Clean The Bypass Small Line On Front Use New Copper Seal Washers, A Kit From Jc Whitney.com Also Rubber O Ring Metic Kit One Fit The Leaking Alda

You are not really too hot
 

First, you need to relax. 100 Deg-C on an 84 300D is really not that hot. I have owned several of these models and over 250k miles or so they tend to run around 100 Deg-C. The issue is probably not with the coolant system anyway. In these vehilces, unless you have an obvious problem with the cooling system, running too hot is usually a sympton of poor combustion. I recommend adjusting your valves and see what happens. This is a fairly easy job for a DIY-er, but you will need the special wrenches and a good set of feeler gauges. Replace the valve cover gasket as part of the job. The next thing I would try is running some "Diesel Purge" through the fuel system, or better yet, have your injectors professionally cleaned (this is a lot more $$$). I bet you engine smokes a little on acceleration. That's another indication of poor combustion. But don't worry about 100 Deg-C. Until you start to get up to about 120, you will not damage the engine.

Check out the diesel forum for guys who know more than I about this.