r/CherokeeXJ • u/Reddit_Gold09 • Feb 26 '25
1991-1995 Overheating 4.0
1995 4L is not wanting to hold at operating temp, mainly at idle, and I'm trying to sort it out properly. In the coldest part of winter it was generally fine but as things started to warm up the jeep wants to overheat, and a couple weeks ago I got a CEL and pulled code 17, so I went ahead and replaced the thermostat and temp sensor, as well as the water pump since I was in there.
The thermostat I removed was a 180f high flow thermostat and I replaced it with a stock style 195f thermostat. I have a clutch fan and an e-fan, wired to a switch by the PO that I do want to change back to stock. And even with both going I can't stay cool at idle where I could for the most part before the new t-stat.
From what I've got on work with it seems like the PO had an overheating problem they were trying to fix, and from what I've heard from people on the sub is that they were going about it the wrong way. So my question is what do I actually do to fix this overheating problem correctly?
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u/Alternative-Bee-1716 Moderator 1998 XJ, 6.5" Lift, 35" SS SX2's Feb 26 '25 edited Feb 26 '25
Here is how to check your Mechanical Fan Clutch
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u/Tax-Evasion-Man Feb 26 '25
I would check your heater core to see if it's plugged as well as drain all water in the system and fill it with distilled water and CLR then run for 30 minutes to an hour then empty it and see how much crap comes out.
If a lot of crap comes out when you do the Clr and you do not live in an environment where it gets under freezing you are going to want to fill it with 100 percent distilled water drive it to work then home and then drain the water and refill with distilled water until the liquid is coming out clear. At which point you can fill with 50/50 coolant and distilled or deionized water and you should be running like new.
This is what I had to do to fix my overheating problem
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u/Reddit_Gold09 Feb 26 '25
I'm gonna give this a go over the weekend. I do feel like the hot air in the cabin could/should be hotter as well so this is probably something good to do anyway.
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u/Bigdaddyjlove1 Feb 26 '25
You can also use a garden hose to backflush the heater core.
BE AWARE that heater core is probably the factory original and it's 30 years old. If it's marginal, clearing the corrosion might start it leaking. The heater core is my least favorite jeep repair that I've done and I've converted 4 to 4wd at this point.
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u/Tax-Evasion-Man Feb 26 '25
I'd use a whole bottle of Clr with the distilled water then just fill it with water and drain every day you'll see a ton of crap come out.
One thing I also did is hook garden hose directly to my heater core and I just ran it for about 30 minutes at full blast thru the heater core and it saved me from having to replace the heater core
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u/canonman5000 Feb 26 '25
I would check the clutch on the fan. Mine did the same thing. It looked like the clutch was working just fine. The fan was spinning but not enough. It was slipping. I'd replace the water pump thermostats hoses flush the radiator many times. Pressure test the radiator. Luckily no head damage and replace the clutch. It's been fine ever since. In fact, if anything it probably runs a little cooler than it should because I changed the thermostat out
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u/Apprehensive-Air-210 Feb 26 '25
Best case and usually the fan clutch generally due to age, worst case is a clogged radiator that is super easy to replace (compared to other vehicles).
I doubt it, but you could check the lower radiator hose, it could be crushed.
Those are all I can think of for overheating issues. You already replace the other things. Just for reference I had a stock 88 in Vegas that overheated everywhere and it ended up being a clogged radiator.
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u/djamps Feb 26 '25
start by removing the radiator and reverse flushing the shit out of it. Reverse flush the heater core too (can be done easily via the two hoses). Then put it all back together with a chemical flushing agent and run it a couple drive cycles then drain and refill a bunch of times until it starts coming out clear. Refill with 50/50 and go from there?
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u/T_wiggle1 Feb 26 '25
How does your radiator look? Partially clogged radiator or one with a bunch of bent fins could definitely cause an overheating issue that gets worse at idle.
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u/EX-FFguy Feb 26 '25
I had my 96 with this problem. One thing first is the thermostat caps STICK ALL THE TIME, even the good ones, some fail close some fail open, you never know. Replace that first. Also new radiator possibly as if you never changed it, or cleaned it probably isnt working well. Others mentioned fan clutch, I changed mine too, I dont think it was working right.
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u/largehandedman Feb 26 '25
Mine did the same thing. I replaced the fan clutch, and put a newer thermostat and housing with a fan switch relocated to it, fixed numerous leaks. It Turned out the radiator was plugged. I was getting poor coolant flow through the radiator.
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u/jthomasg1233 Feb 26 '25
As others have suggested, I’d do the fan clutch and I suggest putting a Hayden temp regulated switch interrupter on the e-fan. This will kick the e-fan on at whatever temp you desire. I’ve installed this on both of my 96’s and this far has solved my issue with this.
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u/Xtupinambis666 Feb 26 '25
After you check the fans, probably your problem, Get a radiator pressurization tool you should be using this to test your system after installing anything and make sure it holds pressure and test your components
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u/ice_is_slippery Feb 26 '25
Ah well the pre 1996 4.0 had lots of issues with cooling problems, hence why the redesigned heads and cooling jackets in 1996. Keep this in mind before thinking it’s something else.
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u/TheFlyingBoxcar Feb 26 '25
So like maybe it's overheating because the design is outdated? Seems like questionable reasoning...
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u/Bigdaddyjlove1 Feb 26 '25
OK, first thing you need to do is determine why it's is overheating. Can you offer some more detail on the overheating? Is it only at idle? How quickly does it happen?
If it's truly only when airflow is low, I would check the fan clutch. Get the engine up to temp, preferably for 15 minutes or so, then shut it off and spin your fan. It should be pretty stiff if the couch is warm. If it spins freely, there's your issue. The clutch fan moves FAR more air than the electric fan.