My '94 E320 wagon started to overheat. I read all the threads on the subject and it seemed to be caused by the fan clutch, but just to be sure, I cranked the drive belt a bit tighter and it cured the problem instantly.
The belt is not the easiest thing to evaluate without the proper lighting condition and it may seem tight. Mine was well worn on the interior side and it felt tight, but it surely was slipping.

I'd advise all with an overheating problem to first consider tightening the belt. It's the cheapest fix.

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'76 240D-Sold
'78 240D-Sold
'85 300 SD, 165K-Sold
'88 300 TE, 165K-Sold
'64 Porsche 356C Cabriolet- under restoration
'86 560SL 124K Miles-Sold
'94 320E Wagon, 74K Miles-128K Miles JUNKED
'06 E350 Wagon, 84K Miles
07 SL550, 14K Miles

That car has a belt tensioner , so if the belt slips b/c of belt wear, you want a new belt, not an over-tightened worn one.

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A Dalton

Excellent point! I should have added that one is on order and will be installed at the first opportunity. Not at all smart to drive with a bad belt.

I only posted this to have folks with an overheating problem to consider a slipping belt as looking at that big drive belt you find it hard to think of it being able to slip and therefore tend to throw expensive parts at the problem while also changing the belt while you are doing it and therefore overfixing the problem. A pro, of course, wouldn't do that as he sees this frequently, but the rest of us just don't have that depth of experience to draw on.

__________________
'76 240D-Sold
'78 240D-Sold
'85 300 SD, 165K-Sold
'88 300 TE, 165K-Sold
'64 Porsche 356C Cabriolet- under restoration
'86 560SL 124K Miles-Sold
'94 320E Wagon, 74K Miles-128K Miles JUNKED
'06 E350 Wagon, 84K Miles
07 SL550, 14K Miles

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Which is exactly why I pointed it out.