so here's what i've got:

1996 cherokee sport 4x4 4.0l h.o. i-6.

about a week ago the temp gauge started climbing while i was sitting in traffic on my way home from work. the aux fan never kicked in and i had to run the heat to get home without damage. so the aux fan doesn't come on as a result of high engine temp, but it does come on when i turn on the a/c or when i unplug the coolant temp sensor.

this all led me to believe it was a bad temp sensor so i replaced it only to have the temp start to spike the next day with no aux fan. i am now at a point of having no idea what messed up. i feel like the relay and fan clutch are fine as the fan does run with a/c or without c.t.s.

so i guess now i'm just wondering if there's something else that can be checked or if something like a bad thermostat could alter how the c.t.s. performs. maybe the temp sender (unlikely as it's only a few months old) is bad and the gauge is reading wrong.

any input would help, i'm at a complete loss after the c.t.s did nothing...

 

Could be a PCM problem. I have a 98 where the aux fan won't come on till 225* (but it comes on just fine with the a/c)

 

i would love to have mine come on at 225, i've let it get to about 235 without the aux fan kicking in before i cut the engine...

 

also, just in case it's pertinent, my 96 is that fun model between the obd1 and obd2 systems. jeep is actually obd1, but many of the sensors i've had to buy have been for 97-99 jeeps...

 

If the Jeep doesn't actually overheat and blow coolant to the overflow bottle then it sounds like the sender to the gauge may be pizzled and there was never a real need for the auxiliary fan to kick on.

 

check your connections that go to the electric fan and the sending unit in the radiator If it has one in the radiator. My connections got messed up somehow and had to splice in new ones.

 

You mention the fan clutch but that has nothing to do with the aux fan.

Heating up while stopped in traffic can be a symptom of a failing mechanical fan clutch so you need to check that first if you haven't already done so.

Pretty much the only way to really know what is going on with your engine temps is to measure at the thermostat housing with an IR thermometer. The gauge on my '93 kept showing increased temps while the IR thermometer showed that everything was . normal. A Mopar OEM sending unit "fixed" that problem.

If your Jeep is actually overheating, you need to fix that condition before worrying about the aux fan, with the one or more of the usual: flush, thermostat, water pump, radiator and cap and mechanical fan clutch.

 

Check fuses and relays might have one for ac circuit and one for cooling fan circuit.

 

update:

i swapped the coolant temp sensor again, and now the aux fan is triggered by temperature once again. it just gets to about 235-240 before it kicks on. i'm going to agree that the temp sender could be shot and giving me a wrong reading on the gauge.

i will be flushing coolant and replacing the thermostat because i don't like the current temperature situation and it's time anyway. as for the fan clutch, i'm not really sure how to diagnose it as good or bad. i'm not going to try the "stick something in it when the engine's hot" method so play in the fan is all i've got and i'm not sure how to read it. when the engine's cold the fan will give about a 1/8 revolution when spun by hand. when hot, the fan will give a 1/4 revolution. for all i know, the fact that there's resistence but it's not locked means the clutch is good, but the fact that it doesn't spin free when cold means it's bad. any advice would be grately appreciated...