I have a '91RS, 305tbi, A4. The cooling fan won't turn on when the temp gets too high. It works fine when the AC is on. I have replaced the cooling sensor on the intake manifold, and still the same. Actually since replacing that sensor, the car does not start/run properly when cold now. The parts store list a cooling switch and a cooling fan switch. I think I need the fan switch, but where is it located on the motor? I think there is a sensor/switch under the #1/3 exhaust ports on the block. Is this it?
Thanks for any help,
Kevin

 

the fan switch is located in the pass. side head, between #6 & #8 exhaust ports, the sensor you replaced is the engine coolant temp sensor (ECT), if it runs worse after you changed the ECT, put the old one back in and return/excange the newer one, its probably faulty

the sensor between #1 & #3 is the sender for the temp gauge on the dash

 

Thanks! I'll try to find the one on the pass side this weekend. Man, there are alot of vacumm lines on that side of the motor! I think that I will have to swap out the ECT also, as when the car is cold, it doesn't fast idle now. Unfortunately, I can't put the old one back on. I had replaced it due to it's plug housing was broken.
Kevin

 

my car just has a switch under the dash that turns the fan on. its alot easier.

 

Its fairly simple to install a manual switch, you can also replace the temp sensor in the block.

 

I have both the fan switch, and a manual switch in my car, I run the manual switch when I am racing, so I can keep the engine cool, it's nice on most third gens, all the fan switch does is provide a ground. if you need a new fan switch, but don't have the money, just splice into the wire running to the switch and ground it to the body so it'll run anytime the key is turned on