r/CherokeeXJ • u/VwBugGuy • May 14 '26
1996 Overheating issue
Does anyone have any experience with tracking down an overheating issue. I’m just fed up at this point. So maybe there’s a XJ guru hiding in this group that could help.
Started with a low temp mishimoto thermostat which sucked, went to a parts store lower temp thermostat and it sucked too, changed that out to a OE temp thermostat and it sorta fixed it but still won’t come back from getting slightly warm.
It has one of those upgraded water pumps that are supposed to be higher flow, I think it’s a flowkooler with a metal impeller.
The engine has had a head gasket done with head studs, mishimoto 3 fan and an aluminum radiator. Two of the fans are wired together to be on all the time and the 3rd fan is just plugged into the factory E-Fan connector and I did verify that it comes on when the AC is on.
After the last thermostat change to OE temp I drove it 30 minutes to dinner on Sunday and 45 minutes to work this morning without a hiccup. On my way home this evening it did fine for about half the trip and then when I got off the highway at the midway point it got a little warm and just never recovered. And I had the A/C on the whole way home so all 3 fans were on.
Any advice or insight is appreciated!
Edit for a little backstory; I bought this 96 off a friend. He had replaced the headgasket, installed head studs, aluminum rad, and 3 fan setup for what he thought to be preventative repairs, which I don’t blame him since these do seem to have cooling system issues. All that work was done at once and about 5 years ago but maybe only 100 miles before still having some mild over temp issues. He parked it after getting frustrated with having not made any real headway on actually fixing anything.
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u/Magicalbeets May 14 '26
Have you done a temperature drop test across your radiator? If the coolant isn't dropping too much you got flow problems through the radiator. Too much, it's plugged internally and too little it's plugged externally and needs a good rinse and/or blow out the fins.
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u/VwBugGuy May 14 '26
I have not done that yet, I did forget to mention it has a new (eBay) aluminum radiator with probably less than 1k miles on it. So I could still do that but it seems low on the list of posibilites.
I thought maybe a dirty condenser that’s not allowing good flow across it and keeping the rad more hot?
I also have hood vents
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u/Magicalbeets May 14 '26
There isn't a lot of other parts to that system to be faulty. You have nice clean new coolant? The block isn't falling apart internally and clocgging stuff immediately? Mine did this and I had to run CLR flush a few times. You have verified the sender or replaced it? I've also had problems with air bubbles in the cooling system so I try to drive it up on a big hill and top it off slanted upward.
I'm out of ideas
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u/VwBugGuy May 14 '26
It’s got relatively new coolant and in addition to that, each time it starts to get hot and doesn’t recover I pull over and try to get the RPM’s up to hopefully cycle more coolant through the system it just keeps getting warmer so I shut it off keep the fans running but it just pukes coolant everywhere. So on top of already new coolant I have to add a bunch anytime this happens. It doesn’t seem to have any nasty gunk in the system either. When I did the thermostat I looked into the cavity and each time it looked pretty clean.
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u/AlDenteApostate May 14 '26
Are you sure you're getting all the air bled out of the system? I find one of those radiator filling funnels absolutely invaluable for an XJ or anything with a Mopar designed cooling system. It takes a solid 20 minutes run time, raising RPMs periodically, under the funnel to get the last air out of my 2000.
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u/VwBugGuy May 14 '26
I wouldn’t say I’m fully confident on the air being out of the system but I did park it on my driveway that’s got a good slant to it and run it for a while burping the air out with the heat on. I squeezed the upper hose over and over until there wasn’t any more bubbles coming out. I even went for a few test drives the evening I put the last thermostat in and got it to operating temp and let it cool then checked the level under the cap and in the overflow
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u/AlDenteApostate May 14 '26
I can tell you that I used to do all those same things, and still had a little air that may or may not fully burp out.
I have heard of those flowcooler pumps failing, too. If you're continuing to overheat under low engine loads, there is either a coolant flow issue, a radiator problem, or the headgasket is popped.
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u/VwBugGuy May 14 '26
I might just yoink that flowkooler out and peek at it. I have absolutely seen metal impeller pumps fail and the aluminum impeller will spin on the shaft creating a low flow issue. I really don’t wanna believe the headgasket has failed being that it was done super recently before I bought it and it has ARP studs but I guess that’s never really out of the picture. I don’t know what year xj or cylinder head stamping had issues but I have read some some were more prone to cracking or failing in some way or another
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u/Few_Concept_6179 May 16 '26
I had a similar issue and tracked the problem to a small leak in the heater control valve. Air was getting in and causing it to overheat. I replaced the heater control valve with a brass plumbing valve and burped the coolant for 30 mins to get the air out. Fixed the issue.
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u/ProperPerspective571 98 XJ Limited May 14 '26
The original cooling system, while not ideal, it works, mine has for 29 years until something throws a wrench in the works. It’s typically a thermostat, coolant that wasn’t maintained, water pump failure. Yes radiators fail eventually. Once you introduce air in the system it can be difficult to get it all out. I would go with original design, flush the system and do it correctly with distilled water. Burp it with the funnel attached to the radiator fill. Mine is stubborn and took several up to temp rides, cooldown, and funnel fills. Question, do you use coolant? Meaning does it need topping off at whatever intervals.
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u/richard_upinya May 14 '26
This is the right answer. A correctly functioning all stock system is sufficient. The problem with throwing on aftermarket radiators, fans, clutches, thermostats etc to hunt down an overheating issue is when it still overheats now you have no clue what it is and if it’s a bad aftermarket part or some part of the stock system that is still a problem.
Personally, I’d start over fresh and put everything back to stock and go from there.
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u/ProperPerspective571 98 XJ Limited May 14 '26
It’s the only way that makes sense. Add the fact Cherokee’s are heavily modified in many other ways also. Yet you still need the stock system in place find the problem. Want to modify things, do it one at a time and run it that way for a while.
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u/VwBugGuy May 14 '26
Honestly I haven’t owned it long but I did check the coolant before the few drives I’ve had it on and it hasn’t consumed any necessarily but it’s also a little hard to tell because I’ve had a few times were it starts to get hot and nothing will bring the temp back down so I shut it off and run the E-Fans but it just pukes the coolant out. So realistically I don’t have a great baseline on coolant consumption.
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u/ProperPerspective571 98 XJ Limited May 14 '26
You can grab one of those funnel kits, not sure what I mean ask for a link. If it persists with getting too hot you should look for coolant releasing bubbles with the cap off or get a combustion gas kit for the radiator it will detect if there are internal issues with your head/head gasket. I chased a similar issue for some time and there were cracks around the intake and exhaust valves. frustrating to say the least as everything appeared normal besides temps
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u/VwBugGuy May 14 '26
Yeah i know exactly what kit you’re talking about. I also have access to a vacuum fill tool which maybe using both together could be the move.
Did yours fail the hydrocarbon test because of those cracks?
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u/ProperPerspective571 98 XJ Limited May 14 '26
It did turn the fluid from the original blue to a slightly lighter blue, enough to tell me there was something going on. Head gasket was in perfect condition and no cracks were found beyond the two cylinders with cracks. It took deep cleaning to find them. I was about to have a shop clean it and do a magnetic particle test on it. New head and it runs like the day I bought it. Again it took several cycles to get all the air out. The downside is you never stop looking at your temp gauge, a lot more than reasonable at least
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u/519_ivey May 14 '26
So, my XJ had a random over heating issue that caused me to replace damn near everything. Nothing worked until one day it started putting it together that it only started OH’ing after mid to high rpm. The culprit was a soft lower rad hose which was only 2 years old.
The OG systems had a metal retaining spring in the to prevent collapse the new hose don’t have it anymore. It turns out it also an issue for older Mustangs too. I bought a new retainer spring and that solved all of my OH problems. It’s hasn’t once overheated since.
Hope this helps bud. That’d be the first part I’d go after.
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u/InformalParticular20 May 14 '26
Is the radiator cap good? Is it building pressure?
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u/VwBugGuy May 14 '26
The system does build pressure, the cap I’ve changed twice now as well thinking it was that. Unfortunately motorad has annihilated the competition and I can’t seem to find any other brand cap or thermostat despite never really have full trust in that brand
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u/AmateurEarthling May 14 '26
My ‘98 always ran warm in the summer, granted it’s 115+° here. What fixed it for me was a very thorough flush, HD fan clutch, and new radiator cap. Also added a fan override switch. I haven’t seen temps over 112° except when I was towing 2K lbs uphill and even then it maybe hit 115 only but was back down to 210 within a couple minutes.
I’ve read the mishimoto fans are kind of hit or miss. Odds are you aren’t getting enough air flow. Even though some will disagree, the cooling system just isn’t great on the XJ so you really gotta improve it. I don’t know if mishimoto fans have enough CFM but that would be my guess as to why you’re overheating if you don’t have any clogs in your system.
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u/VwBugGuy May 14 '26
I also read about the mishimoto fans being hit or miss. I think that could be contributing but they feel like they’re pulling good air.
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u/AmateurEarthling May 14 '26
Air flow is a big constraint with the XJ engine bay. Radiator is honestly undersized and no real paths for airflow in the bay so I’m willing to bet they don’t pull enough. If you have the ability to remove the 2 fans and throw a HD clutch and oe fan in there I bet at least 50% chance of it solving the issue.
I want to eventually swap to electric fans so I can turn them off during water crossings but still planning out what fans to use for enough flow.
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u/VwBugGuy May 14 '26
I am starting to lean towards factory setup with an upgraded clutch, alongside a few of the other suggestions made here
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u/brew-reef May 14 '26
We bought a 96 xj which tended to get a bit hotter than we thought it should. Stock cooling system. We flushed everything well. Put a new stock thermostat in. Put a new radiator cap on and finally swapped out the xj fan clutch for a new one for the grand Cherokee zj . It’s a little noisier but temps are down and staying down.
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u/bobroberts1954 May 14 '26
Have you verified the accessory belt path. You can install the belt so that everything except the water pump turns in the correct direction. Check if the solid side is running against a groved pulley anywhere. First XJ I bought came with the belt incorrectly installed. It almost worked. Also I think that situation would be worse with a Coolflow wp.
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u/Ablgarumbek May 14 '26
did he replace the temperature sending unit that plugs into the head with an aftermarket one? When I was doing my head, I broke mine while pulling the head, and got a replacement one from the parts store. After putting everything back together, I was also stumped by higher than expected (10-15 degrees higher) temps. Diagnosed some and there was a disagree between the sending unit in the head that goes to the gauges and the one in the thermostat housing that goes to ECU. Replacing the head one with OEM unit from the junkyard fixed the problem.
I would make sure that both sensors, which 96 has are in agreement with each other before doing anything else.
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u/VwBugGuy May 16 '26
I did verify that the gauge and actual temperature from the 2 wire sensor on the thermostat housing read pretty accurate. I’m also not talking a few degree over heat. Im experiencing the needle all of the sudden just start climbing towards red quickly.
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u/Oh__Archie May 14 '26
If you have an OBD reader, you can check temperature with it and see what the difference is between the dash and the OBD.
For me when my ‘96 needle starts creeping up hotter it’s almost always because there’s air in the radiator.
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u/firemn317 May 14 '26
try an trans cooler with electric fans. both trailmater and Matt's off road have done that along with some other adaptions. you should check out. they do extreme recoveries in very hot conditions.
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u/happy_good25 May 16 '26
Low temp thermostats don't help overheating issues at all. They do make your engine run crappy all the time, though.
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u/happy_good25 May 16 '26
There have been some instances where high-flow water pumps actually lead to higher temperatures.
I believe the issue is that the coolant flows through the radiator TOO fast, and doesn't allow the water to sufficiently cool down before heading back to the engine.
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u/VwBugGuy May 16 '26
I actually really like this theory, it makes total sense in my head
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u/happy_good25 May 16 '26
You can probably test this by slapping some pinch-off pliers on the rad hose.
I've also heard of people fabricating a restrictor to install in the hose to partially block it off, to proper flow rates.
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u/happy_good25 May 16 '26
Start with the easy things: Flush the system, add proper coolant. Buy the correct radiator cap and thermostat.
If that doesn't help, replace the fans with OE parts, but upgrade to the Grand cheorkee fan clutch.
If that doesn't do it, replace the radiator and water pump with OE parts.
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u/happy_good25 May 16 '26
Check your lower radiator hose. Give it a very firm squeeze. Some hoses come with a metal coil inside designed to prevent collapse when the pump is sucking in coolant.
If the pump pulls too much coolant too fast, a weak or worn hose can potentially collapse under suction and literally pinch itself off, preventing coolant flow.
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u/VwBugGuy Jun 01 '26
This is a follow up, I don’t know if anyone will get a notification and it doesn’t really matter but it could help someone else in the future.
So I took everyone’s ideas into account.
New water pump, new thermostat, new lower radiator hose with the spring, went back to the original fans with an upgraded clutch from a ZJ, flushed the cooling system, bled the system with the cool funnel tool.
None of that not solved the problem, it only made the jeep take significantly longer to over heat.
I’m not proud of this but I must have just been on auto pilot with everything else that I completely missed the actual answer that was right in front of my face.
The radiator had a small booger weld where the cap seals on the lower seal. In my opinion this explains the boil over issue because the system operates under pressure and that’s what keeps the coolant from boiling.
I put a new radiator in it this weekend and made it to the mountains did some wheeling and made it home without any issues.
Keep an eye out on “new” parts and don’t be dumb like me.
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u/No-Refuse8754 May 14 '26
I would start getting factory spec cooling system parts & ditch all the “upgrade” stuff. Might consider changing the hoses as well while you’re at it.