Temperature Sensor

I have a 1994 XJ with the 4.0. Is their only one temperature sensor on this engine? The one on the thermostat housing? I don't see one in the radiator like my old 90 XJ had. Does the sensor in the thermostat housing control when the electric fan turns on and off?

It has been running hotter than what I like - about 215-220. I have noticed that the electric fan isn't coming on so I figured the sensor must be bad. I know that the fan works because it does come on with the AC.

Thanks,
William Crawley

Your 94 has 2 temp sensors. The one that you've found talks to the PCM, and probably is bad if the fan doesn't come on. The second one is at the rear of the head next to the valve cover. This one is hooked to the idiot light or the temp gauge, and (apparently) has nothing to do with engine operation.

If you're running warm, you may also want to consider a new thermostat (OEM preferably, it has an air bleed) and/or a flush & fill. If it creeps up quickly you may have other issues than just a bad switch.

ChiXJeff

ChiXJeff,

The thermostat and flush/fill were the fist things I tried. I also replaced the clutch on the manual fan and I checked to make sure the fins in the radiator were not clogged. That is why I am pretty sure it must be the temperature sensor. If not, I have heard there is a relay that controls the electric fan too, so, that will be the next thing to check if this doesn't work.

Thanks for the help.

On the '94 the temp sensor in the thermostat housing feeds data to the ECU, and the ECU controls the aux fan. There is still a relay, however. You can easily check the relay if you have a/c -- turn on the a/c. If the fan comes on, the relay is okay. If not, the relay would be a prime suspect.

And by the way, on my '94 4.0L, the electric fan comes on at about 230* too hot for my liking. I checked it against a mechanical guage inserted into the hose between the thermostat housing and the radiator.
Patrick.

I have an 88 and the electric fan runs ALL the time....I have ignorantly thought all this time that that was normal? I don't have any cooling problems but I am the third owner of this particular XJ. I guess maybe a previous owner direct wired it or something, or could I have a bad sensor somewhere as well?

Third owner, all bets are off on that one LOL. I've know third owners to find bananna peels in trannies and differentials to keep them quiet long enough to get rid of. The sensor could be bad or it could have been hard wired as a quick fix for a hot running problem instead of fixing it correctly. I'd probably go with the relay first and if thats a no fix keep it as a spare. Toss up on finding a hardwire, depends on how well it was hidden or blended in with the other wiring. All that said, jeeps are known to have oil pressure sending units bad out of the box so a bad temp sensor would not suprise me.

230*, I don't like that at all. Is there some way to get it to come on around 210* without a manual switch? While wheeling this weekend I was able to keep the temperature fairly reasonable (it usually stayed under 220*) by keeping the defrost or AC on so that it would cycle the electric fan on. But, I would prefer to just have the thing come on at 210* so that the engine never got up to 220* in the first place. If not, I may just wire it to run all the time.

Thanks for all the help!