How might a person go about diagnosing a faulty fan clutch? If I have been driving on the highway and come to an offramp and stop my temp goes way up but then after i get moving again in regular in city traffic it cools off a bit. Is this a symptom of the fan clutch?

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1983 300SD White with Grey interior

It might be .... but if you do a search for fan clutch in our archives I know there are some great threads in there which should answer your question and more...
It may be that your Aux electric fan is not coming on... if you have one...

Just saw that you are in Florida... .have you cleaned the bugs off your air conditioner condenser and your radiator....and straightened any bent fins ?
When did you change your antifreeze last ? Have you ever flushed your cooling system according to MB instructions ?

The fan clutch is designed to engage when the engine heats up. Easy way (although not definitive) to check is to spin it when cold, then try the same with the engine hot. Should be noticably tigher when hot.

If the temp goes up over 100°C. when you hit traffic, the clutch should be fully engaged. Shut off the engine and attempt to turn the fan by hand. It should be difficult to turn (but not impossible). If it spins freely, like it did when cold, then the clutch is the culprit.

Depending on maintenance, it might be time to checkout the radiator thoroughly. They accumulate debris inside the fins that you cannot see. You must remove it from the vehicle and thoroughly clean it with solution and compressed air in an attempt to get the fins clean.

If it is the original radiator, seriously consider a replacement.

Thanks. That has really helped me in atempting to single out the cause of my overheating problem. So i know its not the fan clutch now and I intend on replacing the thermostat as well as flushing the radiator. After driving today though i found an interesting clue....After shutting off the engine at 80 degrees centegrate i went to feel the back of the radiator upon which i desicovered that some parts were very hot and one slarge spot in particular was relativeley cold. I am assuming this means the radiator is blocked up and would flushing it out be enough to remedy this problem? If so what flushing agents do you guys suggest? Thanks again for all the help.

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1983 300SD White with Grey interior

degresing cleaner......followed by Citric acid flush......do a search on citric acid flush....might help if it doesn't the radiator will need rodded out.

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Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

If it's the original radiator, it's on borrowed time. You have problems internally due to clogged passages. I'm quite sure you have problems externally due to clogged passages. Do yourself a favor and change it for the peace of mind. You won't regret it and it will save you hours of misery.

You can have the radiator tested but it's highly likely it's blocked and needs to be replaced.
Personally I would hate to pull it out, attempt to clean it then put it back and have it not work again.

Danny

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1984 300SD Turbo Diesel 150,000 miles

OBK member #23

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