How about the gauge? For some reason my cooling system sits at 230 all day long untill I climb a hill, then it spikes up like crazy almost to the white line before the red. As I stated in another post, I have a low mileage motor, new heater control valve, new 195 degree thermostat, new water pump, new clutch for fan, new fan blade, new shroud, new 3 core radiator, new temp sensor for computer, and new temp sender for the gauge, and obviously new coolant. All this within 4000 miles and it still runs that hot. Hoses feel fine like they should when they should. It blows my mind why its overheating, I don't think theres air in the system since I bleed it with a handy bleeder valve I installed on the top heater box hose. My last guess here is that the gauge could be wrong, or for some crazy reason a bad head gasket, but theres no water in the oil, I just changed that and theres NO sign of water. There is no smell of coolant out the exhaust or excessive water vapor. Just telling my story so far, no need to reply unless you want to PM me. This tread already has 2 people with problems

 

I believe Zachqb2 also said his problem manifests itself when he's going uphill. Naturally going uphill means more load, more throttle and therefore more heat generated. Just let me throw this out there... Could there be an air pocket trapped in the motor that under normal driving stays near the back? But when going uphill slides towards the stat or temp probe?
In order to rule this out do you have a trailer you could hook up to your jeep and tow? With a decent amount of weight in there this would simulate the load of going up the hill. If it overheated with a load on flat ground we would eliminate the possibility that going uphill has something to do with it.
Mike

 

Here's an interesting writeup about an XJ cooling system modification that might be helpful. http://jeephorizons.com/tech/xj_cooling.html
You might also want to use a timing light to verify that your timing isn't advanced a little. That will also cause overheating under load, while not exhibiting any adverse affects under normal driving conditions. JMO, Dan.

 

Old Blue; What do you think about his use of the 180 degree thermostat?

 

I hereby apologize for the misinformation above. After checking my manual I find the timing is controlled by the PCM and is not adjustable. Sorry, Dan.
My ZJ runs about 210* all the time, and if it weren't for my OCD I'd pull the 195* out and put a 180* in there. But I just can't bring myself to go against the book.

 

OK, my problem sucks. Seems theres no answer to it. I pulled the rear sensor out and no air, I jacked up the front end to bleed it, and no air. I just got back from the dunes with the quads on the trailer, pulled hills and drove like heck on the freeway and only on the hills was the temp spiking. I am also geared wrong, 33" tires with 3.55 gears.

 

You're a lot braver than me to keep driving a good low mile engine at those temps. I have no answer for your overheating issue. I'd run a 4.56 gear to keep it from lugging with those 33"s though. JMO

 

Yeah, I need to re-gear but funds are low since I work in construction and things are slow. I want to save up for a locker in the rear too before I dig into it. I don't drive too far 99% of the time. Its a 5 mile round trip commute to work every day. I am going to try and bleed it again today...Maybe I'll force feed it with a hose.

 

You could try the old tried and true method of removing the cap and having a friend keep the rev's around 1500 rpm's. Once the stat opens it will purge everything. That's how I just did mine and it worked well.
Be careful... Break the cap loose with a thick towel over it.

 

I've been reading this thread pretty intently over the last few, and wanted to mention something that I ran into. Hope this doesn't go too long; apologies if it does:

I've owned my Jeep for 1.5 years, but have driven it for 10 years (long story.) In the last couple of years, I have noticed the temp creep up a bit from 205* to about 215* - I figure that she is due for a radiator flush soon. One thing I noticed was that the temperature sending unit (for the gauge; the one at the back of the cylinder head) seemed to "wobble" a bit - turns out the sending unit was cracked at the base (the insulator, not the brass, threaded part.) I replaced it with a new one from my favorite auto parts store, and the next thing I know it is running MUCH hotter. I of course think of air bubbles and all sort of other issues, and spend the next several days fretting over it and not driving it. My laser temp gauge reports 215* to 225* on the t-stat housing; much lower than the gauge shows.

I replace the sending unit again (second replacement, 3rd sender overall), and get a slightly different reading (cooler, but still too hot to be comfy). While swapping out, I crack the insulator (accidentally) and decide to compare it to the original one (also cracked.) Surprise - they look NOTHING alike. The original has a flat "blade" style connector hidden in the insulator, while the replacement part has a spring (!) inside the insulator.

3 sensors, 3 different readings. Exasperated, I actually used superglue to put the OLD unit back together (I didn't expect it to work, honestly) and install it. Surprise, my temps go back to where they were before (205* to 215*), the glue holds (still holding, 3 weeks later), and I am back where I started several weeks ago, minus $50 for two sending units. My next one (remember - I am still using the cracked one and it could fail at any time) is gonna come from the Jeep dealer or the junk yard.

Bottom line - I think I was chasing a non-existent problem. I think my ol' girl is running a little warmer than before (age does that to us!), but that the different readings cause me to go off into the weeds. Also, I got different readings from different parts, and even parts that look identical on the outside are radically different on the inside - and you may not know unless you break 'em open.

Can you verify the temp with anything other than the gauge? If others can test and report their temps (with laser sensors, from a common, agreed upon area), it may help those of us who may (or may not) have problems to figure out what is normal, and eliminate the gauge as a variable.

Sorry for the long-winded post, and possibly hijacking the thread, but it looked like the best place for it, since everyone was getting involved... Hope this helps a bit.

 

I just noticed that zackqb2 (the originator of this thread) just sold his Cherokee...

 

NeosXJ -- I appreciate your post, thanks.

I have an infrared (IR) thermometer and it was helpful in verifying thermostat housing temperature. Its reading pretty much agreed with the dash temp gauge. I got my IR therm. on eBay for about $50. I was amazed at approx. 600 deg F temp on my exhaust manifold!