This is just a post to find out how the 87 300D Turbo engines cooled when they were new. Mine has a 14 head. The question I have is this: Should my engine go from about 85-90c to 100c+ at a normal traffic light stop? I see it rise fairly quickly, about 1 min or so to just under 100c. I have owned nymerous diesels, mostly Fords but one 240D 1982 yr. Now it is usually around the early 90s Far. and I have the AC on. My electric fan comes on and the fan clutch seems to be working good as well. All my other vehicles never heated up as rapidly as this one. No pressure from a gasket or cracked head either. My Powerstroke just sits around 195*F in the same conditions. Given that it is 7.3L vs 3.0L means the ac will have less effect but that much? Could I add a manual idle control such as the 240D has in it to increase idle? Is the engine just under cooled with not enough capacity? Or do you think I have other problems? I read where some guy drilled some holes in his tstat. Does that help? Bigger capacity radiator? The car runs and performs well. TIA
Bud

Sounds a little odd to me, but if it never breaks 100°C, I'd forget about it. My car spends a lot of time in the 90-95°C range but almost *never* cracks 100°C. Forget ideas of drilling t-stat holes, upsizing the radiator, etc... the cooling systems on these cars are plenty adequate when working properly. BT, DT...

In case you haven't seen this, I recommend all 1987 300D/TD owners read this:
http://www.w124performance.com/docs/mb/articles/124.1x3_buying_tips.txt

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Dave
Boise, ID
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not sure if this applys, but on my 300SD the impeller was made of steel, and the replacment i got at NAPA was made of brass. the steel one had alot of pitting on it and the holes in the impeller were about twice the size as the ones in the new brass impeller... due to the corrosion the pump worked, but not properly. if i had to guess and you had the same style pump on your car i would think that is your problem... the water isn't moving at the correct speed so its not as effecant as when it was new. its probably not a problem unitl is gets above 100C.

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You know its pretty cheap insurance to replace the waterpump,fan clutch and thermostat .And it really doesnt take that long to do,make sure you fill the upper hose when installing.

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85 300sd SOLD ,85 745i,95 740i,1972 Suburban,1938 International

gsxr, thanks for your reply and yes I had read the info. The temps do go above 100*C but not much. The water pump was replaced by the po and the cooling system flushed. But I don't think the tstat was changed recently. The fan clutch looks new also even though the fan is steel bladed. I don't know why the water pump was changed but the car has 175k on it. The temps when running 15mph and up it cools pretty good. I live in S. Mississippi and the heat has been brutal lately. Guess I will buy a tstat and start there. What do you recommend for a replacement? SN84, thanks and I really don't know what kind of pump used for replacement. I also may do an acid flush since I don't know what the mechanic did. Thanks.
Bud

Here's a few more tips:

1) Definitely change the t-stat... use an OE/dealer part, or OEM (Wahler/Behr). It's not likely this will cure things, but it's cheap insurance, and it's a good starting point before replacing bigger things, like the radiator.

2) Make sure the radiator AND condenser fins are clean and free of bugs, leaves, debris, etc. A proper cleaning requires removal of the radiator.

3) Check the fan clutch - when temps are 100-105°C, pop the hood and kill the engine with the "stop" lever on the injection pump. The fan should stop almost immediately. Compare to when temps are 70-80°C, when cooler the fan will spin for a few seconds after the engine stops. If the fan isn't engaged when hot, either the clutch OR radiator is the problem.

4) It's a good idea to replace ALL the hoses in the engine compartment (2 large, 3 small), especially the upper radiator hose (this one gets the most heat stress).

5) Make sure you use either MB coolant, or Zerex G-05, which are identical... both are light yellow in color (not green, blue, orange, etc.) Click here for more details on why. (1.7MB PDF file)

6) Although this should NOT affect engine temps, it's a good idea to make sure the electric fan high-speed switch is working. This triggers the electric fan on high speed when temps reach 105°C. It's hard to test this unless temps actually get that high. If the switch has not been replaced, or if you are not sure the fan has ever come on HIGH speed (it comes on low speed when A/C refrigerant pressure exceeds either 16 or 20 bar), it's a good idea to replace it on principle. Almost every W124 engine I have worked on that is older than ~1990 had this switch defective.

7) If the radiator is original or old, it's possible the radiator is the cause of the high temps. My car had the radiator replaced in 1993 by the dealer, and less than 4 years later in 1997 (when I bought it), the car was running between 105-115°C in the summer (in Sacramento). After replacing *everthing* else, with no improvements, I finally replaced the shiny 4-year-old radiator, and temps instantly dropped back to normal (85-95°C). Just something to keep in mind...


Hope this helps!

Gotta Love that Sacramento Summer!
gsxr, That is exactly how my car was acting before I replaced everything including my radeator... now it never breaks 100C

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