Auxiliary fan refuses to work

[The_Nietzschean]

I have replaced the auxiliary fan switch on the radiator and the coolant temperature sensor to no avail.

I know that the fan works because it comes on with the AC.

Could someone walk me through the steps of testing the switch? Imagine you are talking to a complete noob who knows next to nothing about car electronics (I just figured out what a ground is for...yea for me). I have also heard that it may be a resistor. What is that and how can I check/replace it?

Thanks

[jlevie]

If the fan works when the A/C is on, it is operating. That is really the only time that the fan should operate as its purpose is to ensure airflow over the condenser and radiator when A/C is in use. If the engine driven fan clutch is good the aux fan should never come on when A/C is off.

[The_Nietzschean]

Well, my understanding is that the fan also comes on when the coolant reaches a certain temperature. That is why there is a two speed fan switch on the radiator.

[jlevie]

That is correct, but when the A/C isn't in use the engine won't get that hot if the mechanical fan is operating properly. The temp switch in the radiator trips for low speed at 91C and for high speed at 99C. The stock thermostat is rated at 80C.

[The_Nietzschean]

I think you may be right and the culprit of the problem may be the fan clutch. Even so, since the engine is overheating (just past the noon mark) the aux fan should still turn on. It isn't so that is still a problem. If replacing the fan clutch fixes the problem I still have an aux fan that doesn't work as it should.
The bentley manual says that the fan should spin on the clutch with some resistance. I am going to check that right now.

[jlevie]

To check the fan clutch drag a rolled up newspaper against the blade tips while the engine is idling. When the radiator is cold the fan should be easy to stop. But once the engine and radiator are at operating temperature it should be hard to stop the fan.

A clue as to where the problem is lies in when the engine runs hot. If the gage settles at half or a bit below when the car is being driven at speeds of 45mph or more with the A/C off, but runs hot idling or in stop and go traffic the fan clutch, air in the cooling system, a bad thermostat, or a partially plugged radiator become the prime suspects. If it runs hot at speed the thermostat or a partially plugged radiator are prime suspects.

[e30Matt]

The aux fan very rarely comes on before about the 2/3 mark on the temp gauge. The sensor for it is calibrated to a fairly high temperature.

[e30Matt]

If you want to test it, check the ETM for the wire colors running to the temperature switch on the side of the radiator, and jump the low and ground, then the high and ground wires. If the fan runs, everything is kosher.

edit: Worst case scenario, go to your local autoparts store and pick up a thermal fan switch. They run about $15-20 and you can set the nicer ones to whatever temp you want the fan to turn on at. Only requires splicing three wires.

[The_Nietzschean]

im not sure how hard to stop the fan should be when it is at operating temperature. It was fairly easy to do when I tried. Only slightly more difficult than when it was cold.

I need to get something to jump the connectors. Next on my list of things to do but money is tight right now.
Thanks for the input

[Kev]

if you want it to turn on early get the e36 318 switch i think thats the one i got if not mistaken ( correct me if im wrong anyone) and check your fuse if it doesnt turn on... and check your resistor ... my fuse blows every 15 times it turns on...

[jlevie]

im not sure how hard to stop the fan should be when it is at operating temperature. It was fairly easy to do when I tried. Only slightly more difficult than when it was cold.

That is a bad fan clutch. It should be very difficult to stop the fan when the radiator is hot.

[Ceeker]

That is a bad fan clutch. It should be very difficult to stop the fan when the radiator is hot.

like he said; the vicous fluid in the fan clutch reaches op temperature and locks up causing it to spin faster to cool the engine. When the engine is cold the fan clutch spins freely with just the momentum of the moving pulley.

This is why you are able to stop the fan with even your hand (not recommended mind you) while the engine is cold. When hot this is also NOT recommended.(Grin) So chances are, if you can still stop the fan from spinning then your fan clutch is fried. get a new clutch.

Remember when replacing it! it goes on with a reverse thread 22mm open end wrench- preferable a thin walled wrench to fit in.

the 2 sp aux fan is just for diff op temps. Sometimes the a/c works harder so it needs more speed to cool the load on the system. Motor works harder to support this need.