jeepuser98

I've got a 96 Cherokee sport. Been awhile since I've had a jeep. First bought it it ran hot. So I replaced radiator, therm, therm housing, water pump, hoses, coolant flush, sensor on therm housing. After I did that it ran for weeks at around 190 never would get to 210. Today it randomly jumped to 210 and steadily would climb slowly up to about 215 before I shut it off. Runs just below 210 going down the road. Aux fan is not cutting on at 210 like on the old jeep I had. Aux fan does cut on with a.c. on. Someone told me to check aux fan sensors that there was one on the radiator and back of the engine. I put a new relay in still does the same thing. I'm not sure if any of this is normal or if I just got spoiled running at 190. Let me know what you guys think. Thanks.

EZEARL

Your auxiliary fan comes on at 217-218. The sensor at the back of the engine is for the temp gauge or idiot light. Besides these gauges aren't known for their accuracy. Most here use a inferred laser thermometer aimed at the t-stat housing to verify the temp. I noticed you didn't mention replacing the fan clutch. If you haven't and don't know how old it is replace it.

97grand4.0

I think it's supposed to hold at 210? There is something about it not going into closed loop for the obd2 if it's below 210. Remember I got hosed up a couple years ago with running at 190 even tho had a 210 stat, but the stat had one of those bleeder holes. Changed to a Stant and held nice @210.
Also my son's XJ the aux fan seems to come on regularly even at idle. Dont know if that helps. And yes am sure there must be a thermistor temp sensor on the radiator for the aux fan.

jordan96xj

jeepuser98,

Some of the information will change depending on which 96 you have. An early build 96 will be more like the 95, and the later build 96 will be OBD2, and the temperature sensors are a little different.

If the rear temperature sensor near the firewall is actually on the intake manifold, then that is the intake air temperature sensor and is not used for the gauges/idiot lights at all. There is no sensor on the radiator that controls the electric fan. If it is a late build OBD2 96 Jeep, the only sensor in play is the Engine Coolant Temperature sensor in the thermostat housing. It is used by the computer to control the electric fan, and the internal gauges and/or idot lamp. The electric fan will come on always with AC or as needed when the temperature reaches about 220f (some report between 218-220f). Mine comes on at 220f on the dot (based on the computer data interpreted from the sensor, not a dash gauge).

The computer should go closed loop before 210f. But at < 200f it might start to complain about things being to cool to go closed loop. I don't know what the official cutoff is though (its probably in the FSM somewhere).

Based on the temperature climbing while driving, and not turning into a full overheat situation, the symptoms sound like a thermostat that is opening late. Another symptom of this will be on cooler/cold days you'll see the temps go over 210f, then dump down to 204 or so, then slowly ramp back up, and repeat. (this same symptom seen while idling is more associated with a fan clutch that is not working).

You might want to start by testing/replacing the thermostat. You might have just got a dud. It may be something else, but that is a quick and cheap place to start based on the information.

By coincidence, I just replaced my thermostat for the exact same behavior. It used to stabilize at 210f pretty well while driving, but lately I would get these short climbs up to about 217 (at most) then it would fall quickly back down to about 204 and start the cycle again. The new thermostat solved the issue. (I have a digital OBD2 dashboard and can see the temperature from the computer at all times, and have alerts set up on it, so I'm always pretty aware of what the thermostat, fan clutch, and cooling system are doing).

jeepuser98

Thanks I have put a new fan clutch on the jeep. My jeep does not have a sensor on the radiator just the one on the therm housing that's in the cooling system. Drove it last night with the A.C. on and it never would climb. Aux fan was on. I'll probably replace the therm just for ****s and giggles. Before that I plan to let it idle with the A.C. off to see if I can ever get the aux fan to come on. If it doesn't at idle at temp when the a.c. is off any tips on what to check?

EZEARL

Mine can sit and idle with or without the a/c and the aux fan won't come on. yours sounds normal. If there's any way you can get your hands on an inferred thermometer I'd use it while your letting your XJ idle.