1994 E420 Overheating at idle
 

Recently my car began running hot at idle. The High Fan is on full blast. The coolant reservoir is full. no leaks. The Clutch Fan however is easily rotated by hand either hot or cold. Their is just a hint of resistance when hot. Is this the problem?

I have checked all the fuses and they seem fine. High and low fan seem to operate properly. Ideas.

Change the viscous fan. This is the problem.

When I said I could rotate the viscous fan I meant using one finger I can flip it so it will turn 1/4 turn while hot. Shouldnt it be locked solidly at high temperature? I really dont have a feel for normal fan bahavior. Car runs hotter than normal all the time. Idle with AC on seems to push it near 120. I turned the heater on and got the temperature down to avoid damage. Do you still think I should change the viscous fan? Why not a stuck thermostat or broken water pump?

I would change the termo first..they open late as they get old.
......get the Behr /80C...

You mentioned the viscuous fan clutch. Have you looked at the modification on Jim Forgione's web page? http://pages.prodigy.net/jforgione/MB_vfc.html

This may be a long shot, but if the clutch is not locking soon enough, maybe modifying it to be locked full-time would be an alternative to getting a new one.

What's a high fan? What's a low fan?

Aux Fans

I would have called them the left and right, unless maybe I was lying on my side.

High and Low are not fan locations..they are in reference to the fans speeds..........
..High fan is for coolant of 105 and low fan is for a/c high side pressure.

..which is why he wants to look at thermo first..he claims it always runs hot , so I assume that means regardless of ambient...and Viscous is air temp sensed, whereas aux fans are coolant temp sensed..so , a high fan at any ambient points to either a blocked radiator/debries between rad and condenser/ or a faulty thermo..and any Tech will tell you the easy diagnosis is to change the termo first b/c of probability percentages.
We see so many guys change fans and radiators and Vicous units, etc...and then they finally change the Thermostat..............go figure ????????
If conditions point to a possible thermo problem, change it and get it out of the equation. One of the few diagnosis that a part change is in order for confirmation. It is not to say that is Definately the problem, it is to say that it is Highly Probable and easy enough to confirm by replacement before getting into the $$$$ trip.

The other cheap fix is a new radiator/tank cap, under $10. Fan clutch is over $600 on that car for some reason.

Do the steps contained in MENU#17 in the aqua table.

Problem solved -and I am broke.
 

Ok, here is the latest. Mechanic agrees it is the Viscous Clutch Fan and replaces it. The part was almost $600 for this particular model car. The car still overheated. Next he says the radiator is plugged because it has cold spots. I ask him about the thermostat and he is convinced that the car will not warm up gradually if the thermostat is stuck. We spend another $700 on a new radiator -he says we need to be sure and replace the TS just to make sure. The problem is now fixed and I am now broke. Tell me where I went wrong? Mechanic says overheating the radiator can collapse the plastic "tubes" inside the radiator blocking flow. This sounds like crap to me. I am not sure they didnt sell me a radiator I didnt need. This really bothers me because this mechanic has been really good in the past. Give me some opinions.

Post #4 and #9.
I have seen it a thousand times...
ALWAYS change the thermo FIRST...PERIOD

There is only ONE WAY to diagnose a late or slow thermo...change it .

Your story is old hat and it is a shame ..

He should at least refund the labor on the fan clutch and radiator ($700 for a radiator?? Big pile of B.S.)

If he has been really good, he should have no objection.