Cooling Problem - Aux Fan???
 

I have an '88 300SE with 250K+... still running great. :cool:

Today I noticed that while stopped in traffic my temp gauge kept climbing. As soon as traffic began to move, the temp went back to normal. I later pulled over and allowed the temp to climb while the engine idled with the AC on. I noted that the aux fan never came on. I later verified that the fan was OK by applying direct power.

My question is, could it be a temp sensor?? Do these fail??
Where is the temp sensor located for the aux fan??
Is there anything else that might the problem?
Maybe a resistor?
Any suggestions are greatly appreciated.

Could be the AC high pressure switch, it depends though on if the pressure in the AC system was high enough to turn it on, this would be low-speed fan, it could also be the low speed relay.
The engine temp has to be quite high (usually up over 100c) before the high speed fan will come on, so unless you were really that hot, I wouldn't worry about the high speed fan but maybe the low speed fan.

Gilly

Thanks Gilly.

Actually, the temp did rise over 100c,,, it was just south of red linning without the aux fan turning on. In the past, I would usually hear the hi speed fan cycle on and immediately see the temp drop. My aux fan is the single, larger type. Any other thoughts??

When I mention "high speed" and "low speed" fan, it is the SPEED of the fan, not "one fan is high speed" and "the other fan is low speed", I realize there is only 1 physical fan.
Try shorting together the 2 wires on the high pressure switch and see if the fan come on low speed. If you juped power and ground to the fan and it runs, you need to find out why it isn't coming on. You can also check fuses in the small auxillary box where the fuse are for the fan.

Gilly

Thanks again.
Sounds like the small auxillary fuse box is a good place to start as I didn't realize there was one for the fan... :eek:

auxillary fan not working
 

You can also check fuses in the small auxillary box where the fuse are for the fan.

Gilly[/QUOTE]

Hi need to know where this fuse is located...had my mechanic hotwire the fan to work with the ac ...Thanks for all inputs :o