I have a problem that occurs once in a while in my '85 190D....
After a 30 minute drive, coolant comes out of the overflow tube.I have replaced the radiator cap, no change. I noticed that the Aux. fan never comes on, even when the engine gets hot in stop & go city traffic. The fan works when you apply 12volts to the plug. My guess is when the engine sits after a long drive, it heats up and therfore boils out of the overflow. If the fan would come on for a few minutes, I'm pretty sure my problem would be solved. I would like to check the thermo fan switch but I can't find it! I found the sensor that controls the main fan clutch (on top of the thermostat housing) but not the one for the aux. fan. Are they the same???
Please let me know!!!
Ken
Hot Under The Hood

 

I forgot to mention that this happens after I shut off the car.
Ken

 

Hi,
Not sure about your car but I have a '86 190e and I don't think I have a auxillary fan. I have an additional electric fan in front of the radiator that would be used whenthe air conditioner is on.
I had a similar problem as yours where the coolant would leak after the carwas shut off. I found that the coolant was leaking from the radiator and not the overflow as I had thought.
Does your radiator cap need replacing?
Jim

 

I've got an 84' 190D and had a similar problem a few months ago as you are now. Your car, even if the auxillary fan were to kick in, shouldn't be overheating period. On my w201, I've never seen the aux. fan turn on even at high operating temperatures. It's most likely not functioning like yours and should be fixed though . Underneath your front bumper there is a sensor. Whether or not that's the right one I have no idea.

The most likely culprit is the thermostat itself, a $20 fix if that is the problem. You also want to inspect your radiator as JLHowie said. See if there are any leaks or debris stopping normal air flow. On the inlet neck at the top, see if it isn't cracked and that the hose is firmly connected.

When I had an overheating problem, I replaced the radiator immidiately ( $100 diy vs $800 mechanic). That didn't solve the problem so I bought a thermostat and replaced the old one. The car runs stunning now (even with a non working aux fan). Just a thought on which way to go....

 

When your car's warm too, check the bottom radiator hose on the left side of the car's engine bay. See if the hose is collapsing, causing a lack of coolant flow andcreating buildup and high temps thus overflow.

 

FYI...I have a new radiator cap.
The radiator is clear and functioning OK.
Last night I found that applying 12v to the fan resistor (mounted on the lower right front fender well) didn't start the fan. The plug was bad. I repaired it and 12v turned on the fan.
This morning after driving to work, the fan still didn't turn on, however after I shut the car off, the temp didn't rise much above the 80 degree mark. It may have topped out at 90 degrees which probably isn't hot enough to trigger the fan.
Anyone have any other ideas?
Ken

 

Fan comes on when it's either extremely hot outside or the engine is hot. You probably fixed the aux fan though