Auxiliary Fan Diagnosis (Done lots of searching and need confirmation)

[dr.gonzo]

My aux fan doesn't turn on when I bridge the wires of the temperature sender. No low or high speed. I do hear the relays clicking. Is that my auxilary fan resistor?

[bimmerteck]

High speed not working and low speed not working would point to the fan itself, Low speed not working and high speed working would indicate a faulty resistor.(assuming the relays/fuses are good)

[dr.gonzo]

I jumped the fan on high and only high worked, I did it a few more times and it stopped working, If I'm going to do the auxiliary fan I'd like to upgrade the radiator and fan as well since I will be moving to AZ in the near future. Any suggestions on set ups?

[dr.gonzo]

Would this radiator work? http://www.ebay.com/itm/Aluminum-rad...ab2b53&vxp=mtr

[Jaxx_]

if now high isn't working, confirm that the fuses are good. If it still isn't working, check relays. If only high is working, inspect resistor on the fan.

You haven't listed the engine that you have, but I'll tell you that even idling in traffic on 95F days my m10 can be cooled with the stock setup and no mechanical fan without issues.

[dr.gonzo]

Sorry I thought I had that in my sig its a 91 318is

[vpilarrt]

No, that ebay radiator will not fit the late model 318 regardless of what the ad says.

[Gregs///M]

I suggest you download the ETM and analyze the Aux fan section. There are three wires at the temp switch, one of which must receive hot from the underloader relay, fuse 19 on 325i, maybe different fuse on your car but functions the same.

This hot wire is switched, depending on temp, to trigger the high speed or normal speed relay. Those relays directly power the aux fan.

The clicking you hear are relays not resistors. Analyzing the schematic, you can systematically troubleshoot where the problem in your system lies. I would start with verifying your fuses for the aux fan circuit. Then verify your relays are indeed working.

[dr.gonzo]

Thanks for all the help guys, I just checked the aux fan with the AC on and it wasn't turning on so I'm pretty sure the fans dead. I'm looking at SPAL fans currently and a couple of aluminum radiators. Other than the expansion tank (i've seen people use metal ones) what parts are needed?

[e30kawi]

I had the same issue with it not coming on, even replaced the thermo time switch. But when I jumpered them high and low worked. I asked the mechanic at work about it today, he said I might be in danger of burning up my ignition switch by doing that. Am I in danger of burning my ignition switch up, or am I turning on the power through the relay by turning the key forward?

[Gregs///M]

I had the same issue with it not coming on, even replaced the thermo time switch. But when I jumpered them high and low worked. I asked the mechanic at work about it today, he said I might be in danger of burning up my ignition switch by doing that. Am I in danger of burning my ignition switch up, or am I turning on the power through the relay by turning the key forward?

If your jumping the pins at the thermo switch or the relay, you are not endangering anything but the jumper wire if its too thin.

Most often, even the best mechanics, know crap about electrical.

[Gregs///M]

You are basically replicating normal operation of the thermo switch or relays.