On my 92 400E I noticed that the engine temp was a bit high this summer (85 c instead of 80 exactly) and now since the weather is colder it is between 45 c and 80 depending on the day. Is the thermostat the only thing that could cause this? I assume it should be at a constant temp no matter what the outside temp.

If so, is this a simple job on the V-8 or one of those take-the-car-apart jobs!

Thanks!

John

92 400E
01 ML 320

 

Possible but unlikely the thermostat if it reads only 45 AFTER the car has fully warned up UNLESS it is a long way below 0 deg! Your V8 pumps out loads of heat unlike some low output euro cars so even with the thermostat fully OPEN I would have expected a temp in excess of 45.

The following test MAY help confirm between the possible diagnosis. (watch fingers!)
From a cold start does the radiator gradually get warm or does it suddenly get hot after a few minutes. The later SUGGESTS the thermostat is working correctly.
Does the interior heater work effectively on these cold mornings? If YES SUGGESTS the thermostat is working correctly

How about the Engine Temperator sensor?

 

the heater seems to work fine, though we have not had any really cold mornings. I will try your suggestion and take some infared temp readings just for kicks.

Thanks!

John

 

Remove and refit the temp sensor connector a couple of times. Any change?
Stuart