Mio3 W124 Thermostat Stuck Open? - PeachParts Mercedes-Benz Forum

d2bernhard · #1 11-06-2003, 01:37 AM

I searched and found no one with this problem.

Outside temp is currently in the 20's around here. Took a 50 mile highway trip in my ‘86 300E this evening and temp was way down at the mark between the 40c and 80c lines the whole time (60c, I think — if I understand VDO gauges correctly, it it is not evenly in the middle). Car also seems to take a while to warm up in the morning.

My thermostat is stuck open, isn’t it?

TomLatos · #2 11-06-2003, 05:23 AM

Sounds like a good guess. You can try another simple test - when the car is cold, squeeze the upper rad hose - you should be able to hear the drizzel valve jiggle (it's that little hole in the thermostat and it's valve) as you force coolant thru it. If you don't here the sound, that too would inicate that the stat is open.

BobK · #3 11-06-2003, 06:39 AM

Also, when the engine is warm, the top hose will be a lot cooler than you would expect. Thermostat is cheap. Order one and a new o-ring to go with it. If you haven't flushed your cooling system in 2 years, its time to do a flush and fill andyway. Even MB antifreeze is cheaper than a new radiator. If you have the plastic thermostat cover, order the metal replacement cover. The plastic one crack apart at the hose at the worst possible times. Mine came apart in my hands as I was pulling the hose off.

glenmore · #4 11-06-2003, 11:56 AM

In hindsight, my car was doing the same thing ....until the thermostat broke...in the closed position and I overheated.

The car always seemed to run cool, and in my short commute to work, would not always reach operating temp.

Easy and cheap to replace but oh so vital to the well being of your car.

Change it out and look at the bridge of the thermostat. That is where mine broke in two.

glenmore
1991 300CE

d2bernhard · #5 11-06-2003, 03:31 PM

Thansk All. Where is it located under the hood?

haasman · #6 11-06-2003, 05:14 PM

I have to recommend making sure your gauge is reading correctly.

-Verify the engine temperature apart from the gauge-

I did all sorts of cooling sytem work on the 300E to help its not getting warm enough problem.

It turned out it was a bad connection to the temperature sending unit.

Haasman

d2bernhard · #7 11-06-2003, 10:44 PM

Top hose is hotter than bottom.

Temp gets up to normal when car is at rest, then down again at cruise. (and got hot in the summer with ac on, and also, did not do this last winter.)

More indication of bad thermostat, right?

Again, where is this located under the hood?

haasman · #8 11-07-2003, 12:30 AM

Your thermostat is located under the metal end of the upper radiator hose that terminates on the top of your engine. Three 10mm bolts I believe. Easy to do.

There are several centigrade ratings, make sure you get the one that is rated for you car. Dealerships use the vehicle's chassis number.

Haasman

blackmercedes · #9 11-07-2003, 01:35 AM

Quote:

Originally posted by d2bernhard
...Temp gets up to normal when car is at rest, then down again at cruise.

Classic thermostat symptom.

haasman · #10 11-07-2003, 10:25 AM

It also occurred to me to be sure and check your radiator. Make sure it is warm all over. Several posters have discovered that their radiators were blocked in sections.

Haasman

d2bernhard · #11 11-07-2003, 11:50 AM

Thanks again All.

So it is under the metal 'dome' right. 3 bolts I see there, yes. "Terminates on top of engine" isn't that really the water pump? Just want to make sure I am in the right place! Alldata (which happens to have lousy directions for this procedure, by the way) says drain radiator. My fluid is recent so does not need to be changed. Do I really have to drain all the fluid or can I just let a little bit (how much?)? Also, where is best place to drain radiator?

ciao

glenmore · #12 11-08-2003, 12:49 AM

With my M104, I did not drain the fluid, and only lost a bit when changing the thermostat.

glenmore
1991 300CE

haasman · #13 11-08-2003, 01:25 AM

See item #3 .... and no, you do not drain the radiator, unless you are trying to ensure little or no coolant loss.

Haasman

d2bernhard · #14 11-08-2003, 09:09 AM

Perfect. This'll get me going. I may even have it done before soccer practice at 10am. Thansk again All!

Job done. No leaks. Took all of 20 minutes. Tested part in hot water with my 5 year old before installing. Made a good physics lesson. Temp gauge hovers just above 80c (as the spec on the part is 87c, this seems perfect.) Old one was stuck in there, but appeared to be closed from the top at stone cold. Had to pull out with pliers and broke on the way out so I cannot know for sure if it was broken. Though, there was a piece of rubber caught in the springs -- suspect this moved through from when I replaced my monovalve not too long ago.

anthonyb · #15 11-08-2003, 05:26 PM

Quote:

Originally posted by d2bernhard
Old one was stuck in there, but appeared to be closed from the top at stone cold. Had to pull out with pliers and broke on the way out so I cannot know for sure if it was broken.

This happened to me the first time I changed out a thermostat. Mangled the thing pretty good. The next time, I thought to dig out the o-ring with a pick, and the thermostat popped right out with no fuss.