I have a 94 XJ Sport with the 4.0. It has a 3.5 RE lift but I still have the stock wheels with 235/75R15. A few years back I purchased it with a blown motor. I found a block from a 99 in a wreck yard and had my head rebuilt. I installed a 3 row radiator (brass and copper), t-stat from the dealer, new water pump, new fan clutch, trans. cooler and hoses. Since then it has always struggled to maintain a consistent temp and always runs hot (210-215) when temps rise above 80 degrees fahrenheit. When I run the a/c it does not make a difference.

Even in the winter when it is 20 degrees out it will climb to 210 then drop dramatically to 180 over and over and over. In the summer when I climb the hills to the mountain I have to turn off the ac and be careful as it quickly climbs to 230+. I have replaced everything twice now thinking that maybe something was faulty.

Any ideas would be great, i really don't know what to try next as I have replaced the whole cooling system twice. I am not sure if it is a sensor somewhere that is making the engine run lean (though my check engine light is not on), maybe a bad catalytic converter (I hit it with a rubber mallet and don't hear anything), maybe the 99 block and 94 head don't completely agree (the head was planed and i have had it checked a couple different times for hydrocarbons in the coolant and the tests come up negative). I am just really at a loss for what it could be.

I'm not sure if this would apply/help...but my '98 XJ 4.0L recently had heating issues when attempting to pull a camper with it (20' long,2,700lbs empty...well within it's range on paper). Does yours have both the mechanical and the electric fan? Assuming that it does,what I did was wire the electric unit to a dash mounted toggle switch,so anytime it's heating (or if I expect it to),flip the switch. It's helped mine dramatically (we just got back from a vacation where we not only pulled the camper loaded a few hours down the interstate,but also sat in July 5th "everybody go home at once" Pigeon Forge,TN traffic for 4 hours and 23 minutes to go the 6.6 miles from campground to I40 with 0 issues at 210 or below). My cooling system is otherwise bone-stock.

Something else I've researched and considering,is adding (tastefully :P )a couple of well placed (and molded in) hood vents (like,find a pair on small-medium vents on something in a bone-yard on whatever vehicle,cut holes to fit,install and make look as factory as I can muster). Between the 2 of those,I expect lots of underhood heat (which is an issue with XJ's apparently,from researching and talking to several owners online and in person) to be vented/blown away,literally. FWIW,where mine ALWAYS ran at a steady/consistant 210 without a load/tow/strain,it now runs a consistant 180-ish to 210 depending on what I'm doing (normal driving,towing,trailing,etc).

If yours doesn't have one,maybe find a right size-to-fit off another vehicle and add it?

Hope that helps

Nice I'm glad you figured it out I might try that myself but maybe next time if you write your thread a little shorter maybe more people would answer. It seems long to me but I gave it a shot to try to help your problem. But that seems to be right. If your auxiliary electric fan wasn't coming on the could be a good reason

How is it coming for you

Spoher, I appreciate your detailed description. The people who are able to help will want as much information as they can get.

You didn't mention your fan clutch in that list of things. The rapidly bouncing temp (180º-210º) is something I've experienced and it was due to a wonky thermostat. It could also be your temp sender.

Was the radiator replaced "a few years back"? It's possible that your radiator isn't flowing properly.

I thought 210-215 was a pretty normal operating temperature? This is what mine runs at consistantly.

Make sure your elect fan is coming on and operating as it should be. Also is the fan shroud intact and in place?

HUH? He hasn't posted a solution yet.

OP, I feel your pain. I've been fighting my '98's overheating issues for several weeks now. I've replaced the water pump, thermostat, radiator cap, fan clutch (HD ZJ clutch, more airflow), wired my electric fan to a switch, put hood vents in, and it will still get up to 230 degrees on the highway. Settles down to around 220 in town. This is on 80-90 degree days. A/C doesn't make a significant impact, either. The rad is in great shape and is less than 2 years old. The whole system was flushed till it ran clean, and I'm still running hot. EDIT: Also replaced CTS and verified it's correct with the IR thermometer.

The latest lead I have is that my transmission is running way too hot. I pointed an IR thermometer at the trans oil pan after driving home from work, it was reading 218 degrees. From my research, the AW4 transmission should be running around 170-180. The radiator is not cooling the fluid at all, also verified with the thermometer. The fluid is also slightly black and definitely needs changed.

I'm still hesitant to replace the rad, but it's still on the table. My next troubleshooting step here is to change the trans fluid and install a trans cooler. If that doesn't help, then I will be taking off the cylinder head and redoing the gasket, and doing what I can to clean out the coolant passages in the block, because I suspect they may be clogged as well. I've fought with Stop-Leak that the previous owner dumped in the system before I had it.

Good luck, keep us posted on your findings.

Had a incident occur a couple weeks ago while towing a fairly heavy load in 95+ temps. My XJ never runs over 210 even with a/c at them temps. It didn't overheat this time either (with a/c on full time) but ran in the 225-230 range at times. Come to the same conclusion as you (hoping that's what it is anyway) that the trans fluid wasn't being cooled and affecting the engine coolant temp. I'll be replacing the original radiator and installing the trans cooler I got.

Have u verified the dash temp gauge?........factory gauges r pretty much a joke. What temp stat r u running?.......havr u tested the stat?.....if u r running a 180* stat, 210* seems wacked in 20* ambient and if u r running a 195* stat, 180* operating temp seems wacked in 20* ambient.

Thanks guys for the responses. The radiator is about 2 years old and was replaced new when I rebuilt the motor. It might have 8,000 miles on it. The thermostat is an oe 195 from the dealer. I have a mechanical fan in the passenger side that I have tried both the flexalite HD fan clutch, which just made a lot of noise but did not help with cooling, and went back to a new standard fan clutch. The drivers side has an electric fan that comes on at 220 or when the ac is turned on. I have replaced the temp control unit on the front by the thermostat. The shroud is still attached on the mechanical fan. I hooked up an aftermarket temp gauge because I thought maybe it was the gauge as well but it reads the same temps.

I really appreciate the feedback and hope this updated information helps narrow things down. Thanks!

So, with a 195* t-stat, the aftermarket temp gauge verifies 180*? Have u tested the stat? Coolant should not drop to 180* if the 195* stat is functioning correctly. Likewise coolant shouldn't rise to 210* in 20* ambient. I'd suspect the stat and the rad.

I agree with djb. A stat can sometimes be bad out of the box. All stats should be tested before being installed.

As for transmission issues, if you are towing, get an extra cooler. If you put it AFTER the radiator, as almost everyone does, it will still dump that heat into your engine, right where you don't want it. If you put it BEFORE the radiator, it will dump heat OUTSIDE, and NOT into your engine.

If engine coolant temps r running north of 230* at the hot end of the rad, it's likely that engine coolant temp at the cold end of the rad is about 210*. I would doubt tranny fluid heat would be "dumping/adding" heat to the motor as the tranny fluid would have to be north of 210*. Under the 230*+ coolant temp scenario, engine coolant heat would be adding heat to the tranny fluid so having the auxiliary tranny cooler "after" the radiator would lower tranny fluid heat, no?.

^ I need to make a decision on this to. Where to put my trans cooler. Before or after the rad and in front of the rad/mech fan or not? Read a thread on another site where some were saying that because of the small size of these XJ rads you want let as much air get to them as possible. Hence,keep as little blockage in front of them as possible.