Jeep coolant temperature help
 

I'd really appreciate some input on a 1996 Cherokee Classic 4WD with automatic transmission, AC and 4.0HO engine.
About mid summer I kept noticing the temperature gauge seemed to be reading a little higher than the normal 210 degrees while driving around town for brief 15 minute trips. But after about 30 minutes of intown or interstate driving the temperature would climb to about 230 degrees. Running with the AC on or off seemed to make no difference.
http://i175.photobucket.com/albums/w...3/jeeptemp.jpg
While sitting in the yard with the engine at 2000rpms, I can make the electric fan come on at about 235 degrees. As it also does when the AC is on.
I'm still having this problem with daytime high temperatures of 80 degrees and less. And there is no evidence of coolant contamination.

Here's a list of things replaced so far.
180 degree thermostat
Radiator
Catalytic converter, muffler and tail pipe
Fan clutch
Water pump
Temperature sending unit

Any ideas???

have you actually put a thermometer or a heat gun on it to see if the temp is accurate?

No I haven't spare thanks, I might as well get one and see.
I figured since the electric fan comes on so close to the gauge reading it might be close.

Maybe you need to go to a lower temp thermostat?

It had a 195 degree in it for at least 2 years before the overheating indication and it stayed around 210 degrees.
Got the same vehicle but a year newer with a 180 thermostat and it stays at about 210.

Pull a compression test on your cylinders. These engines are just about bulletproof, but I've seen several of them with bad head gaskets. I had just about the same problem on my 98 Jeep Cherokee Sport. Turned out to be a bad head gasket between number 2 and number 3 cylinders. Fairly easy to replace, just a PITA.

Which sender or sensor did you replace? The fan should come on at 220 degrees according to the CTS. Have you pulled the radiator and cleaned out the condenser yet? As for the guage reading high, I can tell from your cluster it is a 96 or older JEEP, so it uses a sending unit mounted in the rear drivers side of the cylinder head for the temp guage. DO NOT run an aftermarket sender in one as it WILL be wrong. Also the CTS(coolant temp sensor) will be mounted in the T-stat housing if it is a 91-96, and ONLY run an OEM here as well(can't tell you how many aftermarkets have caused me grief over the years as GM and CHYRYSLER both used the same appearing CTS but with different resistance readings, and teh afterm,arket ones get mixed up ALOT). If it is a 87-90 it will be mounted in the lower ceneter portion drivers side of the block, but they use a fan switch mounted in the radiator to turn the fan on and off. Put in a OEM t-stat back in it as a lower temp t-stat does NOT stop overheating, all it does is create OTHER problems like check engine lights, washed down cylinders, poor cabin heat, and only accomplishes making it take a little longer before it overheats. These engines LIKE to run at 200-205, which happens to be the ragged edge of overheating.

Head gaskets do fail on these, but normally once they get run hot and the head gaskets go the rings break in them from it. I've pulled the head and done head gaskets to many times now and had to pull em back down to do rings to do just a head gasket anymore. Head gaskets are pretty easy to diagnose though as when they go you either get teh white smoke and coolant smell out the tailpipe, or the reservoir bottle will overflow.

Let me know if you have any specific questions as I used to eat, sleep, and breath JEEPS before I went diesel crazy. I was even a JEEP tech at a dealer, and was dam good at em. I would pull the radiator back out though if it was mine, and CLEAN teh condenser out REALLY good. This is a HUGE problem area in the JEEPS and often overlooked. Also make sure you got a max cooling radiator. I have had problems with the brass cored units fro mADVANCE, and have had good luck with the aluminum cored ones from AZ. And put a factory sender back in the rear of the head. Your description though sure sounds like air blockage to the radiator.

Lower temp t-stats NEVER stop overheating, it ONLY makes it take longer to overheat.

Thanks FERM, the sensor I replaced is the one at the rear drivers side that disabled the temperature gauge when disconnected. The one at the thermostat housing initiated the electric fan and set off the check engine light when disconnected.
New radiator and no build up in the old one, replaced it anyway. The condenser does have a few flat fins and a fair amount of gravel lodged in it but I can see through a very high percentage of it to the radiator.
This animal has never lost coolant or gave any of the normal overheat indications except for the gauge.
I'm aware of the air blockage especially on the ones that have the funny looking tank. This one has the regular old overflow type.
My next thought was to replace the condenser, basically because of the elimination process order I've replaced prior. Then pull the head and replace the gasket if that don't help.
First I'm gonna do like spare suggested and see if I can determine if the gauge is close to correct.
Keep throwing this stuff this way please!

I would start by going to Chrysler and buying BOTH the coolant temp sensor(one in the t-stat housing), and the sending unit(one in the rear of the head). Eliminate those two from the equation. I cannot stress enough to not use aftermarket parts for the electrical if you don't want to deal with grief just like this. And if there is any debris to speak of in the condenser, it will run hot. Also put in a factory OEM t-stat from Chrysler while you are doign the CTS and sender. It will be a hotter t-stat, but they work much better. I've had alot of problems with aftermnarkets here lately hanging until 225-230 before they open, and then plummet down and work like they are supposed to.