'91 300CE

It has been 80F+ and dry for the past couple weeks and my car has been running perfectly... temp at about 83-87c while sitting in traffic with the AC on.

This past week... its been 65 with heavy humidity and my cars temp will rise to about 95c while stopped at a light with the AC on... not that I am that worried about this temp as it's still below that unmarked line... but I am just wondering what is up.

And when I start going again, the temp will drop to the 80c mark... it never goes that low once its warmed up fully. but it will rebound back to the normal of a tick over the 80c mark within seconds.

Is it the humidity in the air making it harder to cool the engine while stopped and also making the engine run cooler quicker once moving with the moisture in the air?

Tell me if I'm crazy... but is this plausible? Or should I be looking at getting a cooling system flush and perhaps a new thermostat?

PhilipM1

Im having the same probem in my 190e. I havent figured out what is it. I live in florida and its usually humid out. My car will wun hot at lgihts or drive thru's. Once i start going it cools rapidly. If you figure it out, let me know. I dont think its the humidity. I even have a 167f thermo wich is like a 75c i think. and it still does it.

Sashak87

It will be. You notice that a humid 30c feels a lot hotter than a dry 30c? Basically the water in the air has a greater ability to pass on the heat which is why if you want to insulate something you trap air because air is crap at passing on and retaining heat. Your car wont overheat when your driving because you've got a constant stream of cool air going through the engine bay. When you stop the air doesn't circulate which means the hot air stuck in the engine bay will build up to a higher temperature.

'91 300CE

Yep... I have been paying close attention to the temp the past few days... it seems to be normal now that the humidity levels have dropped.

I have also played with different scenarios with A/C on and off and on max and auto and I can get the aux fans to come on with the temp at about 95... which from another thread is completely and perfectly normal... it has never gone to or over the 100 mark.

Thanks... I think I was just being paranoid having only owned the car for a few months.

RobertG

It would help if you were to clean your radiator (externally) using a garden hose or shop air, you'll be surprised how much dirt is lodged in there.

'91 300CE

Interesting that my car runs cooler when sitting in traffic on an 83 degree day... sits at about 85c. Where on a 65 degree day its about 90-95c.