I have read all of the posts regarding the high end of the thermostat readings, but what about the low end? My (new to me) 1994 E320 wagon seems to be working perfectly. It never gets too hot even in the near 100 degree weather that we had here in South Carolina last week. This morning was my first experience with driving it in 60 degree weather. Everything was fine, but I noticed that it took a long time (30 minuter or so) before the temperature reached 80 degrees on the gauge.

Is this normal or might the thermostat be partially stuck open?

As usual, thanks in advance for the great help and detailed replies in your posts.

Jack Wiles
1994 E320 Wagon - and loving it!

Yup, it's either stuck open or it's not even there. I'll bet it's not there..:):):)

I believe mine is failing open as well. In 60-70 degree weather, coolant temp refuses to go above 80, even with A/C on. On the highway, at around 75 mph, it drops to about 78 or 79.

Also, the engine is a much louder when coolant is below about 85-90 degrees. The engine roars, as if the fan clutch is engaged. As soon as the temp reaches about 90, it becomes very quiet.

...and most likely the reason its not there is to compensate for some other problem. So when you put it back in watch your temp like a hawk until you are satisfied everything is ok!

I just realized I resurrected a 5 year old thread.

thermostat
 

i think it is always partially open by your description.if it was not there i think that pump does a short cycle by pass and engine gets hot at freeway speeds.anyway change it and all should be well.

Oh crap. Thats funny I responded to the original LOL :D

yeah, but you were right on with the answer!

tom w