Aux. fan doesn't go on

guys I've been trying to fix my aux fan for a couple weeks now and I still can't figure it out. I know the fan works since it will go on when I turn the ac on or if I unplug the temp sensor. So my question is why won't it go on when my xj get hot, around 220 or higher? I have changed out the temp sensor twice thinking the parts store sold me a bad one, but 2 bad ones I doubt that. what could cause this? thanks

Since the fan is working when you turn the air on, they didn't sell you a faulty fan either time. The normal operating temp is 210, but it should come on when it overheats - make sure you have a full system w/no air bubbles in it so there are no false readings that way. If it won't turn on when it's getting close to the redline, the problem isn't with your fan; I believe it's with the relay reading the sensor.

sictruck said:

guys I've been trying to fix my aux fan for a couple weeks now and I still can't figure it out. I know the fan works since it will go on when I turn the ac on or if I unplug the temp sensor. So my question is why won't it go on when my xj get hot, around 220 or higher? I have changed out the temp sensor twice thinking the parts store sold me a bad one, but 2 bad ones I doubt that. what could cause this? thanks

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Are you changing the sensor in the thermostat housing?? because it is the one that control the fan.

Yucca-Man said:

Since the fan is working when you turn the air on, they didn't sell you a faulty fan either time. The normal operating temp is 210, but it should come on when it overheats - make sure you have a full system w/no air bubbles in it so there are no false readings that way. If it won't turn on when it's getting close to the redline, the problem isn't with your fan; I believe it's with the relay reading the sensor.

Click to expand...

Sorry for the hijack but mine does the same thing. What is it that goes bad in the wiring. I don't know much about wiring but I took a look at mine the other day and all the I saw was a wire coming off the wiring harness by the computer into the plug that goes into the fan. Everything looked good there, but maybe there is something that I'm not seeing.

yeah I did change out the temp sensor on the termostat housing. and today I changed out the relay as well that didn't work either. whats the best way to try and get all the air bubbles out?

Typically, park the font wheels on a curb or large rock and loosen the thermostat housing; some folk fill the hose itself. Make sure your thermostat has a 'burp' hole in the 12 o'clock position so it doesn't trap air

Don't forget to turn on the heater so you can flush all bubles in the hoses, the temp sensor seats in the cavity of the heater hose, when the heater is off the by pass valve leave a small amount of water (coolant) to flow, some guys in hot climates block the heater hoses because they don't use the heater and the problems begans.

What year? That's important, because there were two ways to do the fan (87-90) and (90-up.)

Most of what I know is about the 87-90 stuff, so I'd need to know what I was talking about before I started talking...

5-90

I've got an 87 w/ the same problem, I've wired in a relay switch so I can turn it on and off when I want so its not a big deal to me but if its an easy fix I wouldn't mind having it work right

On an 87, it's either the switch/sensor in the radiator, too much air in the radiator so the coolant isn't hitting the sensor, possibly the radiator is too clogged so that coolant isn't hitting the sensor, the relay the switch is wired to is bad, or something in the wiring itself. If you have air conditioning, there are two diodes in the fan wiring somewhere in the vicinity of the left hand hood latch that can go bad. If you have air conditioning, the auxilliary fan should come on when you use it.

BTW, the switch on the Renix systems closes at 190 F according to the factory.

I think that's about all I know about the Renix auxilliary cooling system. Any other questions, you'll have to get a manual and figure it out for yourself. :wave:

Fred

Thanks, good info there, my bet is the radiator is clogged as I've been fighting cooling issues lately (flex fan helped but still heats up in town). I've got everything except the radiator to swap to the 91+ system and since summer's coming I'll probably get on that

I've had it happen where the sensor didn't seem to ground properly (I know it's a two-wire, but stranger things have happened) and pulling and resealing with RTV Copper saw to that.

If you aren't doing anything else Saturday afternoon, PM me for my addy and come by and I'll have a look. With four RENIX XJ's, I've kinda gotten used to their little quirks (and looking at it will give me a better idea, anyhow.)

Also, check for corrosion or crud in the WP connector. We can assume the relay socket is clear since you get the fan when the A/C REQ signal gets there (there are two "trips" for the stock RENIX fan - the TFS in the radiator tank, and an A/C Request (A/C REQ) signal from the ECM when the aircon is activated. Both trip the same relay.)

5-90