How many miles are on the unit? If it is over 100k and the fan clutch is original then replace it. I'd go ahead and change coolant if you don't know when it was done last. The fan clutch is the part that the fan (the one driven by the engine) bolts to.

I'd be willing to bet this is all due to a slipping viscous coupling on the engine fan.

yep

Ok gents what am I looking at to replace the fan clutch?

Is this a common problem?

Presuming this is a relatively easy job.

Costs DIY?

I am running without the engine fan for a long time and there is no over heating.
The electric fans kick in when its too hot.
Olivier
you also got some replies there:
'99 E300 running a tad hot - Benzworld.org - Mercedes-Benz Discussion Forum

My brain and wallet are starting to hurt with this.

I'm not doubting the fan clutch, but how do I really know it is bad??

Crank the car, get the engine up to temperature as high as you can get it and have someone shut the engine off and watch the fan on the front of the engine. If it stops within about 1/2 turn then it is good.

I'll try to post a video tomorrow night showing what a bad one looks like. The only reason I haven't replaced mine is that it's a little bit of a pain to remove. There's also a cheap solution: You can buy Toyota viscous oil and re-fill the clutch.

A search will reveal the DIY for this.

My fan clutch went out last week at 310k miles. Is no longer free spinning and is locked up at all temps/rpms.

They cost ~$125 on this site. Replacing is pretty straight forward, drop tension on the belt, remove cross member above grill, pull the rad forward like you've already done and remove the clutch/fan, swap out the plastic fan blades to the new unit, and reinstall.

Why do you want to put the rad forward? It can be done without doing it?
Its tight but it work, just don't do it with a hot rad, it burn...

Each car is slightly different Oliver. On mine even with a shorty hex there no room for the rachet. Only takes 5 mins to remove the cross member and gives a couple extra inches so as to avoid scraped knuckles or bent rad fins.

That is right. Man I like the way the radiator cross member is designed in them where it is easy to remove and service the radiator. I noticed it on a Nissan the first time I came up on one like that. Wonder where the first application was of the removable radiator support. That engineer should have been given a raise:).

I'll have to check it out and see. Might try the oil replacement method if it is bad. Just wish I had more time to check stuff out.

I don't use a rachet. Just a large Allen key, might be why? But indeed its still very tight and removing the cross member might be the easier/ pain free option as indeed the rad liked to scrap my knuckles :P

In addition to pulling the rad forward, I've also learned to put a piece of cardboard covering the rad fins. The rad and my knuckles both appreciate the gester.