I've read the recent posts regarding the coolant temp guage. Questions asked were concerning the high readings, and/or what are normal to average readings. But my question is, "what could the problem be (if any), when the coolant temp guage barely moves?" I perceive that my pressure is somewhere around 60 or 70 degrees. It jumps every now and then to 80 or 90 degrees, but on the average it stays low. Needless to say, it doesn't really blow serious heat at me either, but kinda warm. There are no leaks anywhere that I can see. What do you all suggest I do? Or, am I just overly concerned? Thanks in advance for your suggestions.

dmsr

 

It could be nothing and it could be something, If your car is a 90's model year, it should run hot, around 90 C. So you could perhaps have a bad sensor from the gauge, or thermostat could be bad, but the car would over heat, unless you have a safety thermostat, these remain open when they fail, so the car won't over heat. 60 to 70 degrees C is really not bad. What engine do you have? Some run cooler then others. I would be more concerned if the car run over 100 degrees C all the time. Also, do you live in a cold climate, We had some days were the temp barely reached O degrees F and my C280 temp guage barely made it to 89 degrees C. So, unless the car is no running well, I wouldn't be too concerned, you could have the sensor checked to the gauge. Or go to a Mercedes dealer and have the scan the engine for faults. Around here it cost $75, which could be a good investment if there is a problem. Not all engine problems set our lights on the dash board I am told.

 

The reason the thermostat is suspect over faulty gauge/sensor is b/c you also mention poor heater temps. The thermo is sticking open [ common]
The 60/70 C temps are not high enough for proper engine management controls and will give you long injector duration and poor performance. Never mind engine wear..
80/90C are normal running temps on E420.
If you suspect the gauge to be reading incorrectly, have it scanned with a temp probe or check the ohms of the coolant temp sensor. [Single wire sensor/thermistor ...the ohms will change with temp ]

Here are the specs to make the guage/sensor comparisons

60C-110 ohm
80C-67 ohm
100C-38 ohm

 

Very good point, I missed the remark about cabin temps being low. Then the thermostat is a good suspect, more now then any sensors. Get a safety thermostat or Fail Safe type, as they remain open when they fail, so your car doesn't over hear. If there is an application for your car. My son has one in his Acura and he had a coolant leak and sure enought the thermostat stayed open, when the car really got hot.

 

Get a Behr .
Benz also use Whaler, but we have high fail rate experience with them...

 

Benz has a high failure rate in a lot of parts failures these days.

 

Unless MBs don't have a radiator cap (wouldn't surprise me since some models can't switch ASR off) you can see if the thermo is stuck. Remove the radiator cap and start the car when it's cold. If the fluid is moving then the thermo is stuck open.

 

Aux fill resevoir tank. w/pressure cap. Will not see radiator flow in aux tank with open thermo.

 

As a matter of fact my C280 has no radiator cap, as Dalton said thru the over flow tank is your only option.

 

What's the procedure for adding coolant when it's at operating temperature?