E350Phil

Hello all,

Sometimes, but not always, when I have the AC on (blowing cool) the cooling fans will suddenly come on high, and the car starts to overheat. This is not in hot weather nor stop and go traffic.

Actually, it only happened twice. Once while parked, but the temp only climbed a little above what it usually is, but the electric engine fans were screaming loud. I shut it off and back on, and everything was okay again.

The second time while driving, but this time the temp went just about to the red line. I quickly shut off the AC and turned on the heat. The temp immediately dropped back down to normal.

Any ideas what's going on here?

Thanks!

Phil

CaliBenzDriver

seems to me you were overwhelming the engine radiator cooling ability in both cases. What you observed was somewhat normal because of the extreme temperatures.

When you run A/C you are trying to cool your engine with already super heated air.

Hot ambient air heated by all the cabin heat is used to absorb additional heat... don't be surprised if the single fan goes screams until its bearing quits!

Warped heads are never out of question during overheat events. I am not 100% positive if Benz still use the amazing aluminum heads fasteners that were made famous by poping off the V8 ...
✌️

CaliBenzDriver

I've never heard about these engines triggering a Limp-Mode to protect their heads from warping... that would be a relief.

Arrie

Make sure your coolant level is ok. When engine is cold remove the coolant reservoir cap and run it on idle for a bit so it can let air out easier if there is any in the system. Your engine should not overheat like you explain. If your coolant level is ok you either have a water pump or thermostat problem. My guess is the thermostat.

The fans running fast simply tells the engine and/or A/C needs more cooling power and when you turn A/C off and heat on and this drops the engine temperature it means that you have issue in the front of the car. Your engine radiator is not working properly and this is either because it is not filled properly with the coolant or you don't have enough flow thru the system. The third would be the fan problem but that obviously is working.

LILBENZ230

Yep, make sure the coolant level is OK. You're not getting any warning lights? The thermostats in these cars are designed to stick OPEN which would give you a P0128 and the car would never warm up to normal temps, so it doesn't sound like that is the issue. Have you had any AC work done lately? Any work done to the coolant system, coolant added, anything? The engine fan is controlled by the computer and high AC pressure could be a cause. You might want to check the condenser - maybe it needs to be cleaned? Just brainstorming here.

I would get it scanned with a MB specific scanner just to see what it is saying. Even in extreme ambient temps, stop-and-go traffic, etc.. the car should not do this.

I remember a case from a few years back where an E-class kept having similar issues and it ended up being a faulty sensor.. I want to say it was a faulty oil temperature sensor, which was odd. I can't find the thread.

And yes, the cars will go into limp mode rather quickly during an overheat event.

bmwpowere36m3

Engine coolant temps will rise with A/C ON, especially when not moving or in stop and go. Yes, the fan will go 100% "screaming" t he higher the temp. All that's normal. When the OP says overheating... what was the actual temp? Even without A/C being ON, the car will try to maintain 80-100*C. Overheating is in the RED and not just a brief excursion.


That said, checking the obvious like has been stated is a good thing and scanning for any codes (with MB-specific code reader) as well.