Jay Stivers

I live in Arizona and ever since it has cooled off my 2010 c300 has been running cool @60- 70 c.. take awhile to come up to these temps and does not reach 80c. got a 0128 code.. possible bad thermostat? Stuck partially open? Fluid level is ok ,fan is not running ....thoughts.

michail71

Might be interesting to see if you can get a cable and log the coolant temp. That gauge looks nothing like the actual temperatures from the ODB-II data.

Carsy

These thermostats fail open. You should find details here in the stickies.

ghlkal

I agree. Likely a bad thermostat stuck open.

manny26

It is the thermostat stuck open I had this same issue last winter also , it gets stuck open sometimes in the cold days , it's doing it to me this winter also . I got the code once so far this winter but I'm not gonna bother changing it yet because it's not
A big problem it goes away once it warms up out. And the car engine light stays on even if the thermostat functions normally after it throws a fault code once .

Plutoe

That's not a good practice, I bet your gas mileage has gone to hell even if you only make one trip a year to the drug store!!

MaineSailor

Plus one on the "not a good idea" comment!
Thermostats are there for a reason! Running an engine cold can cause numerous problems, not the least of which is corrosion on the cylinder walls. Replace your thermostat - it's not a big deal or expense!

Alfadude

I agree. Best to correct issues when they are minor before they cause bigger more expensive problems down the road. This one seems like a no brainer. It is cheap and you have the advantage that can do it at your leisure.