Running hot, Oil coolers and turbo vs. non-turbo
 

A long time ago, in a garage far, far away, a grimy parts monkey sold me this radiator and oil cooler combo for some ridiculous price. I bought it on the spot and was d@mn happy about it. I was told it was 'the wagon size oil cooler' and thats why it was so expensive.

Today I bought the larger of the two oil coolers @ the JY, it measures just under 4" in width and I took it from a turbo model. The one in my car measures just under 3" in width and I have no idea what its origin is.

Where is this smaller oil cooler from?

What is the likelihood that my high operating temps are the cause of this small oil cooler? - - I easily reach 100*C on a good 1/4 mile uphill climb in 80*F weather, but it stays right there.

Who has some good suggestions for cleaning an oil cooler, or should a shop do it?

I would just plug the holes and pressure wash it. Then do a run and check the temps. If they are better than leave it, if they are the same try swapping for the bigger cooler.

I really doubt that the slightly bigger cooler is going to keep the temps from reaching 100C.

jt20,

Are you actually running hot? Can you verify the actual head temp with an IR temp gun?

I used an IR gun on mine to find out the gauge was wrong. Replaced the temp sender, and right back to 82 C.

dd

The smaller cooler is likely from a 240d.....the bigger one is standard on a 300 turbo. I doubt the small size difference will make a change in your temps though.

As mentioned, verify its actually running that warm.....and, check the cooling system, it is the likely culprit.

100C is not really very hot. The oil cooler on my w124 does not even start to cool until 115C I think. Although I will have to verify that number.

That oil cooler looks like its from a w115 or R107.

I don't know if they uprated the oil cooler on the 300's at some point but I do know its not from a 240D. The 240D's got a half sized one up to early 79? and then got a taller tube and fin type.

I don't think that your 100*C temp is from the smaller oil cooler. I would not worry about it, MB says things are fine up to 120*C. I ran my 240D in death valley last summer with the A/C on and the needle just below 120*C for hours on end with no issues.

You can find that smaller cooler on N/A 300D's. I've seen people run it in their turbo cars without any problems. But of course that was flat land.

I seriously doubt that the oil cooler has any significant relationship to the coolant temperature, since from a cooling point of view, they are separate systems. However, transmission fluid temperature might have some effect on coolant temperature since it is cooled by the same coolant that cools the engine.

I need to clean the INSIDE

wishful thinking

Im not actually sure, Dan.

I only assume this because my gauge shows 80-90*C during typical operation, once things start getting heavy.. I hit 100*C and stay there until some wonderful cooling opportunity comes along.

agreed, but if that extra heat is all coming from oil that can't lose its heat quick enough.. aren't I adding thermal breakdown to the oil and shortening its lifespan??

Interesting question. Is the oil cooler there to bring down oil temperatures to protect it (the oil)? Or is the oil cooler there in a synergistic way to help bring down the overall engine temperature?

My view is synergistic. Oil can survive very hot temperatures with out any ill effect. I'd guess the 300 degree F or more, but I'd have to research that to be sure. Synthetic oils can run even higher with no problems.

Remember that the oil is jetted up to the bottom of the pistons for cooling purposes on the Turbo models. Not sure about N/A designs though. So if the engine gets really hot the oil needs to stay cooler to help bring down piston temperatures. The oil also takes heat off the head as it drips down into the crankcase. It would be interesting to have an oil temperature gauge installed in a crankcase.

I hear diesels run more efficient at higher operating temperatures. I wonder what the most efficient operating temperature is? 100C? 110C? Higher?

Not sure of it's relevance but I have a recollection of looking into what determined whether or not MB added oil coolers to their cars and vans. I think all the turbo's had oil coolers because of the role of the oil in cooling the pistons but I think I figured out that on NA models, oil coolers were added if the vehicle had AC. That seems to suggest that either the oil coolers played a role in the overall temperature of the engine or that AC caused the engine to run at a high enough temperature that it broke down the oil more quickly.