Overheat at traffic with AC on
 

My 89 300e is experiencing a high temp (110 - 115 degree) while in traffic with AC on. By seaching the site, I found it could be a bad auxiliary fan switch, can some confirm this for me. When the car cruise 60-70 mph on the freeway, no problem at all (85-90 degree) and after driving 30 miles to work, open yhe hood, the auxiliary fan is spinning. So I am guessing the switch is bad and did not activate the auxiliary fan to a higher speed when at stop-and-go condition

Jump the wires on top of the receiver/drier...
 

the fan should work. You can also jump the temp sensor on top of the engine. The fan should work. There is a resistor on the inside the drivers' fender. See if it is still intact. What about the electromagnetic clutch in front of the engine. Is it working?
HOwever, start the basics first. Replace thermostat along with the coolant and check the expansion tank cap.
Good luck!

BTW, what coolant are you running in it? Green stuff? Also what is the ratio of coolant to water? Is it mixed for -40 degrees?

Keep us posted,

Haasman

110 to 115 on a hot day 100 F or above while setting in traffic is not as bad as you may think...

Thermostats open full at about 107 or so.. So thats really about 110 for most of to read on the gage..

Most MB fan clutches come in at 104 to 110 so under about 110 the fan clutch is not working..

The electric fans come on at about 100 on low and go to high about 107 to 115.. so if your car is one of those that runs things in the upper limits 110 to 115 is really where every thing really starts doing what it should..

Above temps are from a Mercedes Factory Manual and cover several models so your should be near those..

In general most of the newer cars tend to run 100 ish to 115.. Newer meaning 88 and up...

I would change the Thermostat and change the anti freeze.. Never a bad thing to do any way..

After that you can park the car nose in to a wall so it gets little air flow .. back of garage or side of house on a hot day.. turn the AC on... Roll the windows down so you can hear whats happening... Run the car up to temp at about 2000 to 2500 rpm..

At some where around 100 you should hear the electric fans come on... about 105 to 110 you should hear the roar of the fan clutch kicking in... and soon after.. 110 to 115 you should hear the electric fans kick in to high.. ..

If all this happens at temps some where in that area.. Odds are things are normal..

Ken

<<Also, about the AUX fan, it has two settings. High speed will come when the coolant temp reaches above the threashold. Low speed will come on when the A/C refregerant temp reaches above the threashold.
>>

I think you will find Low fan should be high side refrigerant pressure activated .

Knowing you and your knowledge of such, I figured it was a typo...

The color of coolant has absolutely nothing whatsoever to do with how hot things get. Green, red, blue, or the urine-colored MB coolant.

Coolant mixture could be an issue if it is an issue. Coolant does not dissipate heat well. The color of it has zip to do with it's ability to do that.

Color is a tip-off regarding the wrong coolant use. If the coolant is the Prestone green stuff, non-Mercedes spec you will have problems with your cooling system including the radiator.

Yes, color of the coolant unto itself has nothing to do with its properties.

How's that?

Haasman