Rauhbatz

Greeting MB World patrons...

My 1991 190 starts to really heat up these days when sitting for a few mins; temp gauge goes almost to the red line. Once I get moving with air blowing thru the engine compartment things settle back down to normal temps.

Given the age of the car I suspect my water pump is giving up or the radiator is clogged. I did have the radiator flushed so I suspect the water pump or maybe an oil change might help...

BTW, I do have a small leak that I top off the radiator but even when topped off it still heats up.

MTI

If you switch on the cabin heater the temps should fall also, which would mean that your aux water pump and heater core switch are working . . .

When idling while parked, does the engine mounted aux fan spin up when the coolant temp reaches approx 100 C? If not, you might have a bad temp sensor, located near the distributor, bad wiring from the sensor, or a failed fan clutch.

SLOPESTAR

I have a 92' 2.6. had similar problem. Replaced the obvious/ radiator/thermostat/hoses/waterpump/tensioner. No more overheating

Rauhbatz

Thanks for the responses so far...

When I turn on the heater the temps do stabilize but are still well above 100C until I get moving down a highway. The aux fan does come on so that sensor does appear to be working. It more just a problem where it heats up almost to redline when idling on a warm day...

My first step is to replace the thermostat (just ordered one). I have the suspicion that the thermostat is frozen in the closed or near closed position and is not letting enough coolant in from the radiator to the blocks.

BTW. is the thermostat inside the housing where all of the hoses and overflow tank connect in the left front of the engine (I have replaced the plastic housing with a metal housing a number of years back)? I have not taken off the housing to see but thought I'd ask the experts on this board.

Gullwing

I think that if the thermostat was closed it would still overheat while moving.
Yes that is the thermostat housing

Mine would overheat while sitting, but was fine while moving. Check the fuses. It is a 16 amp fuse, but my 25 amp still blows every so often.

Rauhbatz

Once I get moving it does start to cool down but not all the way...usually to around 85-95C...I recall when the car was newer it would take a trip thru Death Valley to get it to heat up over 80...

Ill start with the thermostat and also check the fuses....

Gullwing

The car should run at 87 degrees C

If it is running below 80 you probably have a stuck open thermostat

Runninrebel211

Mine runs a little below 80C on the temp gauge when I am cruising on the freeway. On city driving it stays dead on 80C. Before it used to get extremely hot while stuck in city traffic around 115C but now my aux fans turn on at 92 deg C after I switched out to the cool harness. Also flushed radiator with and replaced with MB coolant and a bottle of Royal Purple Purple Ice coolant additive. It really works! My car is a 1993 190E 2.6

SLOPESTAR

We had that problem too and it was directly related to the thermostat and the radiator just being old and for having been mechanically neglected from about 80000m to about 110000m by my brother in-law before me. Those two things looked to be in bad shape at time of replacement so going all the way with the cooling system except for replacing the heater core/exchanger( if there is one?) was all small price to pay when the radiator was already out of the car. keep us posted please!

Rauhbatz

When I took off the hose leading from the radiator I glanced inside the thermostat housing to see what resembled a bin of thermostat parts!

I removed the housing and pulled the old thermostat bits out. The new thremostat went in, put everything back together and went for a drive.

Temps went right up to 88C and stayed there. Perfect!

Thanks to all respondents.....

Runninrebel211

Got pics of these thermostat bits?

Rauhbatz

The spring arms on the top of the thermostat had come undone. For a minute when I took the hose off the thermostat housing I actaully thought it might be the water pump as I could spin the copper arms around the center pin! The center section was resting at a 45 degree angle within the circular housing.

That would explain the reason why it would run cool for bit (stuck partially open) and then heat up (not opening enough to allow flow).

Runs like a top now!