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

all I can think of is using a lower temperature thermostat. I think you did most everything else. I have heard that non OE water pumps dont do the job that well. Other than that I dont know.... For what it is worth my father used to tell me that diesels run better hot...He used to drive buses in New York City and he got me my first diesel. It doesnt seem to be in the dangerzone... It might have to be something you have to live with... how much more time are you going to invest in your ghost in your machine

good luck

I like your threads
You are relentless and I can appreciate that

bob

speaking of the thermostat...i went to Napa autoparts and I bought a thermostat and gasket from them...its not the same as the OE version (wahler) but i was wondering if the unit will fit in the thermostat housing. The design of the new thermostat has a more upward triangle point on the thermostat compared to the walher one. I'm going to put in it today to see if it works...my original thermostat is still stuck in the thermostat housing and i dont know how to get it out. I was told that the thing would just pop right out...but on this one...it feels like its molded to the housing directly. is there a way how to take it out without damaging the thermostat housing?

Thanks for your replies
Allan

Thanks for the help guys!

The Bob: There is not a lower temperature thermostat available as an option. Plus, it should not come down to trying to ‘trick’ the system like that. I really want the root of the problem to be fixed.


Muybweno: The Wahler thermostat that I got IS different from the one supplied by the dealer. I know that people here have stated that Wahler is an OEM supplier, but perhaps Behr or someone else makes these particular thermostats for MBZ. I don’t know. The dealer supplied one looks like what you are describing – the cold side metal bridge is more ‘peaked’, whereas the Wahler is flatter. The Wahler also uses more brass components such as the disc at the end, where the dealer unit is stainless steel.

As far as getting your old one out, I don’t know what model car you have. IF it is like my 84 300D, the thermostat is actually surrounded by a rubber ring that acts as the gasket. The rubber has a slit in the inner circumference and this is where the peripheral edge of the thermostat goes into. It should just come right out with a light to medium pull. On my 117 V-8s the setup is different – on those there is an O-ring for a gasket, and the thermostat actually rests against the metal itself. Other than those two models, I don’t know. Thanks for the help & good luck.

RTH

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.

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

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!

To answer the last few replies:

Donkey: The gauge is definitely reading accurately. Heater core is good, but that is not a factor in this type situation. Diesel grade oil, absolutely; but again not a factor here. As far as $$$ of guesswork – well, I hate guessing. That is why I try to understand the principles as well as the specifics. The only reason that everything was replaced was due to my practice of replacing the hoses & water pump on any car that I purchase. It is cheap insurance; this way, I don’t need to worry about it. Then the radiator neck cracked, so a new one was installed. Nothing much left to change out, but *not* due to random part swapping.

TXBill: Interesting. It appears that you have already been down this path. You have my empathy. Your experience with two cars also confirms my belief that this temperature is not normal. Again, some will argue that it is not in the red, therefore it is OK. That’s bull in my opinion. Something is wrong, and I want it fixed!

As far as your fan is concerned, this is interesting, as my 84 300 does not have a coolant temperature controlled fan. It is ONLY switched on via the thermo switch on the AC receiver-dryer. FYI, most (all?) of the coolant sensing thermo-switches that I have seen for fan control (on the 1970s through early 1980s MBZs) are calibrated to go on at 100 Centigrade (212 on your Fahrenheit gauge). There are dual stage ones, but that’s not applicable here. Let me know what year your 240 is, and I will look up the wiring diagram on my CD. Curiosity may have killed the cat, but maybe it can help cool your car down instead.

If your fan is not coming on with the AC, it will have an impact on AC cooling performance – there is not as much airflow over the condenser and therefore is not as much heat rejection as when the fan is running. This would also translate into a warmer running temp for the engine, as well. BUT it could be the chicken-egg syndrome here. IF there is not enough of a freon charge, the receiver may not get hot enough to trigger the switch (assuming that it is a heat triggered switch). If it is a pressure triggered switch, the same would apply. However, if there is *really* low pressure, the compressor will not engage at all due to the pressure switch which is there to protect the compressor. (And you thought that your post was long? My fingers are starting to bleed.


THANKS AGAIN EVERYONE!
RTH

damm RTH...you mind as well work for MBZ for the diesle line up..since you know so much already. I feel your pain, i have the same problem with my 300D 78. Well i manage to swap up some info from my mechanics office diesle training service manuals. I'm guessing that you cant buy these manuals anymore because they were only used for students attending the diesle college for MBZ. I'm not sure if this stuff will work but here it is:

Engine is Overheating:
1. Insuffeicient coolant in radiator.
2. Coolant circulation is obstructed.
3. Loose or broken water pump belt.
4. Thermostat defective.
5. Air bubbles in cooling agent.
6. Exhaust system restricted.
7. Injection timing incorrect.
8. Inferior fuel quality.
9. Cylinder head gasket leaking.

This stuff is taken directly out of the office mercedes benz service training books...and thats all it says about engine overheating, doesnt even say anything about normal ambient temperatures for the 300D/240D engines.

I've just got done flushing my radiator tonight and I used the BG products to flush out the stuff in the radiator. I took the 300D for a spin tonight (about 65F outside weather) and when i'm cruising around 45-50 mph the temp would stay about 200F. When i stop at a light, and wait for 3-4 minutes, the temp would past 212F line, just a little more than half way from 250F red line. When i get going...the temp drops back down to 200F, no less than that....damm there is something wrong here. do i have the incorrect coolant mixtures when the temp fluctuates like that? I didnt even have the A/C on the whole time.

Also after i flushed the cooling system out, I can hear these girgling sound from the top radiator hose, coming from the thermostat housing to the radiator....thats when the engine is hot...is this normal?

thanks for replies and i hope that some of the info helps out
Allan

is there a way how to get rid of the girgling sound? or should i just drive it for like 30 minutes for the coolant and leftover water to mix with eachother? what should i expect?

thanks
Allan

RTH

Where exactly are you measuring the temp with the temp meter? I believe the water on the engine side of the thermostat is regulated at about 200 (or 88 deg C)with the thermostat. Your 65 deg F water coming in indicates the radiator is cooling the water fine. The water runs through the engine and exits the head and goes into the top of the radiator, picking up heat as it goes. Therefore,it could be alot hotter than the 88 deg C of the thermostat. (This is why we all see temps on our gauges from about 88 deg C to about 100 deg C in summer time driving. The water at the thermostat is regulated to 88 deg C, but the water temp exiting the head varies from the 88 to 100 or 105 depending on engine load etc).

So, here's my theory, for what it's worth. Either you have a lack of water flow problem (very low probability) or you have something wrong like a bad head gasket or something that abnormally elevates engine temp.

I think your cooling system is OK, it's something else. On gas engines, ignition timing WILL cause overheating, I've had it happen on 2 cars. On diesels, I don't think it works that way, but it's probably worth checking, along with anything else, like valve clearance, etc.

This certainly is an interesting problem.

RTH,

I feel for you, I've had problems like this before on another kind of car and it can be frustrating. I'm no rocket scientist when it comes to these cars, but I have to ask out of curiosity, have you ever placed the thermostat in a pot of boiling water to ensure that it opens under the right temperature? I seem to recall doing this several years ago only to discover the thermostat was bad, and NEVER did open in the boiling water, however the new replacement did open when placed in the water. Just my two cents worth and a whole lot of curiosity.

jeric

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 people in the future when they search the archives.

Muebweno: Excellent list that you provided. In my case, all but numbers 7, 8, & 9 are ruled out already. #8, inferior fuel I seriously doubt since I have purchased it from two different manufacturers at 4 different stations. #9, if the head gasket were bad, I would have other symptoms such as *very 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. #7 however, THIS I have not checked. The engine runs very well; I wonder if the timing can make this much of a difference on running temperatures. I mean, if it were significantly enough out of timing, would the engine not run poorly? A point to definitely ponder.

About you 1978 car - I saw on the CD that there are two different thermostat housing types, early & late. I know for a fact that the later ones are self-venting, but I don’t know about your ’78. You may want to try to bleed air out of the system. As far as your temps go, that doesn’t sound to bad actually. The only thing that I would check in your case is the viscous fan clutch – perhaps it isn’t engaging at higher temps like it is supposed to, therefore not drawing enough air while you sit still.

TxBill: I will look at my CD later tonight and get back to you.

240Joe: You are absolutely correct in the description of the flow path of the coolant. I have used the infrared thermometer on several points – on the head & on the block, on the area right around the temp sender to check for it & the gauge accuracy, and on the metal tube leading to the thermostat housing to check incoming water temp. And yes, ignition timing is a factor on gasoline engines.

Jeric: Yes. I believe it’s up somewhere in the beginning of this thread.

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

THANKS EVERYONE!
RTH

RTH,

You've gone through every thing in the cooling system itself. Now is the time to branch out to the other factors that might be causing excess heat. I think somone else pointed to the transmission as a possible source. I can say that I switched to mobil 1 ATF and noticed engine temps go down a few degrees. But I think you should really check injection timing before you go much further. Here is something I copied from the diesel mailing list On the bubble method.

Brian, Buy a used injection line from a junk... 'er, uh..
"recycler" and make you're own (nothing special about it -
just a short piece if fuel line bent into a "J" with a nut
on the end to attach it to the pump). OR use the Bob Sanigar
bubble method (that really is more precise).

> On the subject of diesel timing. If you are replacing the pump or rebuilding the engine. The simplest and most accurate way of setting the pump is: Disconnect the fuel line going into the pump from the filter. Take the spring and plunger out of #1 delivery valve, put the delivery valve back in and snug it down, hold the the pump linkage in the full open position. If you have the drip tube install it on the delivery valve, if not use the injector line in such a way that it is pointing away from the engine. It you don't mind the taste of diesel you can blow through the fuel line or use low air pressure. Put the open end of the injector line in a glass of water and watch the bubbles. Turn the engine slowly until the bubbles stop and check the timing mark. After tightening the pump recheck. This method is really more precise than it needs to be and although it may sound complicated it is very easy . Bob



--
August M. Booth, Jr. Ph.D.
Univ of Pittsburgh School of Medicine
"der Dieseling Doktor" mbooth+@pitt.edu
'87 300TD 143Kmi,'87 190D 2.5 193Kmi, '84 190D 2.2 217Kmi,
'85 190D 2.0 148Kmi, '87 190D 2.5 turbo 200+kmi, '84 190D
2.2 234Kmi dismantled
MBCA, GWSection
http://www.dhc.net/~pmhack/mercedes/mbooth1.htm


I hope this helps and inspires you to get to the real cause of your problem.

Bob D.

P.S. You did check for timing chain stretch last time you set your valve lash didn't you?

hey RTH...where are the bleeder valves in the 300D 78? I notice that when i checked the engine this morning...the top radiator hose was compressed in!!!!..it had vacumm in it...i think I do need to bleed for air but i dont know where the valves are. I bought one of those antifreeze testers to see how much coolant i had in the system after i flushed it...turns out that i only put enough coolant to protect the radiator to +20F freezing temperatures...the normal is i think -40F.....i'm way out of range!!!!! could this be the reason i found vacumm in the radiator??

thanks for any replies
Allan

H2odiesel: injection timing check is next thing on my list, although the car runs fine & the cam timing is perfect.

Muybweno: I don’t know where the bleeder valves are on a 1978. There should be a removable bolt/plug at the uppermost point of the system – look for it in the vicinity of the thermostat – but again, I am *not* an expert on this, this is just an (semi) educated guess.

Thanks guys!

RTH

RTH

You might try this link...

http://www.troubleshooters.com/tpromag/200005/200005.htm#_thermostatbubbleconnection


I found it while searching around for info on burping a cooling system. There some interesting info on figuring out if you have a head gasket problem.

HTH

Joe