engine swap Electric Fan Thermo Switch For M20

[dcmackintosh]

My '02 received an M20 conversion two owners ago, and I've had a few minor things to sort out.  Since I got the car a few months ago the electric pusher fan always came on with the ignition and I thought it must have just been wired that way.  Yesterday I noticed that it wasn't coming on at all, and the temp did climb past it's usual position (parked at 180F on the aftermarket gage).  I know next to nothing about electrics, but I did poke around and determine that there's a relay (top right of the photo) which had switched power, and a thermo switch on the aluminum radiator.  After cleaning the spade contact on the switch and some wiggling, the fan did come on with the ignition.  It also comes on if I touch the wire to the radiator.  The switch appears to have failed closed, at least most of the time.  It also appears to have teflon tape on the threads, which doesn't seem like a good idea, unless the coolant is enough of a ground.

 

I'm trying to determine if the switch is something I can just pick up at NAPA before I drain the radiator.  It's located next to the hose at the thermostat outlet (I assume).  There's also a radiator hose at the same side on the top (the return?).  The rad cap drains to the ground (no overflow tank), if that matters.  

 

Would it be easy to get a matching part without pulling this one?  Does a 91C switch sound good here?  What should I use on the threads?  Any other tips?  Thanks!

 

[M3M3]

All depends on what threads the rad has.

I use a stock bmw e30 fan switch in my car.

Are you sure that is a switch and not a temp sensor? Only one lead on it.

[dcmackintosh]

All depends on what threads the rad has.

I use a stock bmw e30 fan switch in my car.

Are you sure that is a switch and not a temp sensor? Only one lead on it.

Thanks for the reply. Sensor is probably the correct term. You're correct that it only has one lead. I'm not sure how it works internally, but it's obviously intended to make that wire a ground at the desired temperature. I may have to pull it to determine the threads.

[jimk]

That being an aftermarket radiator, it probably has NPT tapered threads.  A BMW switch would have straight threads and won't seal without gumbo or tape.  Look for a US made switch from some racing parts supplier.

[Stevenc22]

Pull the switch and try read a part number off it and search for that part number.

[M3M3]

depends on what the rad was made for.  if made for a bmw, probably had straight threads.

 

ya gotta take the sensor out and see.

[garya]

Just a note... you don't want to use thread tape on a single pole switch.  The tape can mess with the ability of the switch to ground and trip the relay. 

 

You should be able to touch that sensor wire directly to ground with the key on, and the fan should turn on.  If it doesn't..then may not be the sensor.