Hey Jeepsters.

I have a 96 cherokee xj.

I recently did the freeze plugs and radiator. I put it all back together everything runs fine apart from the AUX fan.
I noticed it wont turn on when its meant to automatically.
Instead I need to turn my AC on and off for it to turn on. Ill turn on the ac when the temp goes past half way, the AUX fan will turn on, Ill turn off the AC and the fan will stay on until it gets to half way then shuts off again.
If i manually active the AUX fan it manages the temperature fine so i know its not my actual cooling system it seems like since i put the fan back in after pulling it all apart for the plugs, it isnt turning on automatically anymore.

HELP!

 

Does your 96 have the sender at back of block or does it come off the sensor in thermostat housing? Unplug the sensor in the thermostat the fan should turn on. The fan on spot...driven by temp is APPROX 220ish. Thats further past the 210 mark than you would expect. The next step depends on where your temp gauge info comes from

 

could air in the coolant system make that aux fan not turn on when it should?

reason I ask is because I’m burping it right now and there was still quite a bit of air in the system..
thsr could explain the temp spike too at the stand still after driving…
?

 

Absolutely.

 

Doneso! It was air in the system. Burped it for 40 mins with driver side jacked up to really get rid of the air.
drove the car for almost 2 hours and the temp stayed below half the whole time.
sat in traffic and it went a tiny bit over half but stayed there.

I’m amazed at how much air there can be. Although I did change freeze plugs so it really needed to be burped.