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Discussion Starter #1
My 1983 240D is hitting top temperatures when sitting idle at lights or in heavy traffic but as soon as I start driving again or if I put it in park and rev the engine the temp goes back down.

Any thoughts on what could be causing this?

Thanks
Deborah
 

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this happened to my 1980 300D. another thing i noticed was the cooling hoses would hold pressure for a long time--often overnight. we swapped the head and the problem went away. when we had the head off we found what looked like little tiny ball bearings sitting atop the pistons that we were told were made from water entering the piston.

we swapped heads just to be safe, but it could be that you just need a new head gasket. either way it's a pretty big job.
 

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How many miles on the engine? It could be a number of things. My first guess would be the water pump. Also check the fan clutch.

To check the fan clutch, get the engine to normal running temperature and shut it of. Give the (metal?) fan that is attached to the engine a spin. If it is tight, it is probably ok. If it spins freely, it is bad.
 

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Discussion Starter #4
Thanks for the input

Yes, the engine does have some miles on it - probably just enough for lots of things to start going wrong (185,000).

Thanks for the suggestions - my first thought was the fan but I wasn't quite sure how to go about checking it. Now that I know how, I'll take a look and see if that's the problem - if not, I guess it will at least start the process of elimination...

Deborah
 

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To be clear, the fan will likely spin with some force, but if it seems as though there is no resistance, it is shot.

FWIW, my '81 300D had the water pump go at just about that mileage. The failure likely led to the engine's demise since the overheating warped the head and allowed water to spray into a cylinder. Rust followed and compression was lost.
 
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