97 E320 cooling problems

I recently notice that my '97 E320 was running warmer than usual. On the advice of a friend I changed what he thought might be a "lazy" thermostat. The temp runs cooler sometimes and then will run a full "click" higher at others. There's no way of predicting if it will run hotter or colder (weather doesn't have any effect on it).

The last time that I had a problem like this (believe it or not, it happened with a car that I owned) it was on my '89 BMW 525i. That time it was a bad headgasket.

Any ideas?

[Gilly]

One fairly common problem on the first 3 or 4 years of the 210 chassis is the aux cooling fans, that's the dual fans on front of the radiator (just behind the black plastic mesh grille with the hood open). The one on the drivers side, you can see the hub poking through the grille. Spin the hub and see if the OTHER side spins with it. They are connected by a very thin drive belt, which is prone to rolling off. In effect the drivers side fan is driving the other side fan, which is simply mounted on a bearing, no seperate motor. You should also pay attention to if the drivers side fan seems to spin freely or not, I have had to replace a few fan motors.
Check that out and then reply with what you find.

Gilly

Fans roll together. I haven't checked the motor yet. I'll heat it up and see if the fan is working. Thanks Gilly. These Racine summers can take a toll on cooling systems!

[Gilly]

Yes, see if they run. They will run MORE often with the AC on, they will run at varying speeds depending on the signal from the fan control module. That module is also a trouble spot, so if you don't see the fans ever run, I'd say it's more likely to be the rather pricey module rather than the fan motor, but obviously you'd want to have the aux fan system tested, or at least try jumping battery power to the fan motor (which is fairly easy to do) to see if the motor is capable of running, which if it is kinda points to the module as the fault, but not with 100% accuracy, but pretty darn convincing anyways.
This assumes thet the problem is more likely to occur while plying the shady streets and byways of sunny Racine (BTW is it RAY-seen or RUH-seen? and do I get a free kringle for answering this?)
If this is happening out on the highway, at that point I'd say something else is going on, because with a car with a radiator up front, the fans are "along for the ride" by the time you get up to 30 mph or so.
Another possiblity is there may be an accumulation of dirt, leaves, trash, etc between either the fans and AC condensor or condensor and radiator, which is partially blocking the airflow through the outside fins of the radiator, this would affect cooling in town as well as highway use.
Finally when was the last time that a coolant replacement was done? It's due every 3 years, and I recommend using the MB coolant, not the green stuff.
Doubtful that it's the headgasket, just to put you at ease about that. Unless you check the coolant at spot oil slime in it Usually ona 104 motor you first would notice oil leakage at the block and head seperation point usually at the right front or right rear.
Gilly

Let me address things one at a time.

No leakage at the parting between the head and the block. No "oil" in the coolant. Oil is coolant free. I guess, so much for the headgasket theory.

I removed the plastic shroud and cover that hides the plug for the fans. I used a battery charger and the probes from a volt/ohm meter to test the fan. Fan runs when power is connected.

(I say RAY'-seen. My wife, who's a native Racinian says RUH-sEEn'.) If you figure this one out a Kringle will be on the way!

Also, no obstructions (leaves etc.) around the AC. The dealership that did the service work on the car before I got it DID do extensive work to the AC system.

This problem started a couple of weeks ago after I had the car on the Interstate on a hot day (about 30 minutes). It ran around 90 and then went up to 115. NOW, the car will "pin" to around 110 after driving for 10 minutes @60 mph.

Now, I'm kind of a gauge freak, but no other Mercedes that I've owned has ever run this hot. Normal?? You tell me.