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Sudden overheating, at a loss what to do next

whatwave

NAXJA Forum User
Location
Colorado
I've been having this issue where my XJ stays around 210 creeps to 220 then suddenly jumps up to full overheating. The engine bay gets too hot to touch. It already toasted a head gasket and now I'm not trying to screw around with it.

I've installed an entirely new cooling system (t-stat, water pump, fan clutch, griffin radiator) but the problem persists. I really don't think there's any air in the cooling system. I haven't replaced anything related to the electric fan but I've seen it running prior to overheating.

Up until now I've had to have my indie do the work because my apartment building has become sincerely uncool about doing work in the garage. But I think it's got to be in my own hands now and building rules be damned.

Can anyone offer some opinions on what it could be or what I can do?

Also, I know there are a ton of threads on this but I actually haven't been able to find one where someone fixes the problem. I'll be sticking with this and updating when it gets sorted.
 
good luck. Make sure you have the stant super stat. When I upgraded to the full aluminum rad the Napa premium stat i had in mine made it constantly cycle from hot to cold. Never saw a resolution on the last thread I saw with this exact same problem.

Updates people!
 
its been very hot lately, ive been a tad over 210 when really cruising.

what year is your jeep?

What happens when your vehicle overheats?
Have you shot the thermostat with a temperature gun?
what kind of water pump are you running?
have you tested for the head gasket lately, overheating can cause more issues?
Do you have a proper mix ratio of coolant/water?

Its summer time you can dump all coolant and run water if you like, even a deep clean may be a good idea until everything flushes clean. If a previous owner was "smart" enough to dump snake oil into the engine, cooling passages could be blocked.
 
I've been working through some overheating issues myself lately, with all the high temps we've been getting in southern CO.

I have done the following and its helped somewhat:
New 160f high flow thermostat (for now, planning to put in a 180f soon as the system is sorted) - this has been the biggest temporary help
new higher flow water pump
new xj fan clutch (removed and replaced with dual e-fan setup (8 blade and taurus))
upgraded from my stock 5 blade e-fan ('93 XJ) to a 8 junkyard 8 blade e-fan ('95-'96 XJ)
both e-fans are temporarily on a manual switch, will be wiring to a temp switch soon.

My temp was at about 180f today driving in to work in this 100f heat, going about 75mph most of the way with both e-fans running. I do notice that my temps will spike when I go from highway speeds to lower speeds (45mph or less) but the e-fans are working for now.

A few things I plan to do still, which I hope will help, but will have to report back:
Upgrade thermostat housing for a high-flow variant
Adding a coolant filter (increase system volume, filter coolant)
Adding a second heater core on the return line from the factory heater core (increase system volume, cool coolant returning to the engine from the heater core)
Adding an oil cooler (increase oil volume, cool oil)
Replacing stock radiator with a thoroughly cleaned stock radiator (after filter install, might upgrade, but probably stay with 2 core)
Install hood lifters or hood vents for better airflow (last on my list right now, might not go this route)

I have a week off coming up, hoping to make some headway on this list. Has anyone tried any of these options before?

My XJ is a 1993 Sport 5-spd w/ upcountry package (maybe? Has a LSD rear diff, and factory skid plates) that is mostly stock. I have done an AC delete and relocated the alternator up, installed a '99+ intake, fan clutch delete and dual e-fans on a manual switch.
 
I've been having this issue where my XJ stays around 210 creeps to 220 then suddenly jumps up to full overheating .....

These symptoms describe a cooling system that is not holding the specified 16 lbs pressure. The pressurized cooling system raises the boiling point of water, loss of pressure allows the water to instantly flash to steam.

Typically you would replace the radiator cap and solve the problem. If all your cooling system parts are fresh, and the symptoms persist, you should look at the frost plugs for leakage and to the head gasket for leaking super heated exhaust gases to the coolant.

The stock XJ Cherokee cooling system is not ideal, but with a heavy duty radiator, and regular cooling system preventative maintenance it can handle just about anything except Death Valley in the summertime. No other specialty parts should be required.
 
X2 I run mail all day in mine with ac running in upper 90s with 80-90% humidity with no problems. I have a cheap all aluminum rad from Amazon and I'm only running an 8 pound cap because I'm worried that the heater core cant take the full pressure. Stock components with a 195 stant superstat.
 
After years of owning XJ's, I'm going to finally weigh in on cooling issues. These are my experiences and opinions, and I'm not intending to ruffle any feathers, so I'm not calling anyone out on their expertise. There are far many better and smarter mechanics on this and other forums than me.

The fact of the matter is, that XJ's seem to have inherent cooling issues. There's too much evidence of that to deny it. I've probably read every thread, post, article on the Internet about XJ cooling problems. I've talked with radiator shops and a number of other people about these issues, as well.

I've come to the conclusion that no one really knows what the Eff the problem is with XJ's. Period. One fix works for one person, but not another. Some people, (myself included) do some repairs and it works, while others, (myself included) try a number of things and just put up with the problem. Seems to me hit or miss. I suspect the root problem to some of these problems is a clogged passage somewhere due to corrosion. That's the only thing I can think of. Could also be head gasket issues that people can't diagnose properly. Regardless, no one has ever said that "culprit Z" is the issue and you need to fix that and the cooling issues are fixed. It's always try this, that, and the other thing, usually with mixed results. Here's my experiences with 4 XJ's that I still currently own.

On my 97, 160,000 miles, you couldn't get that thing to overheat if you tried. Have an American Eagle 2 row aluminum radiator, but everything else is stock. Stays just below 210 all day long even in the So Cal desert. Mostly a trail rig, but I can drive it all day long on the street or highway, short or long trips, doesn't matter.

99 2 door, 200,000 miles (current build). Had some overheating issues early on. Looked like PO neglected the cooling system. Changed out the radiator to a Mopar heavy duty, Hesco water pump, new stat, hoses, etc. Old radiator was clogged, but everything else looked okay, just old and dirty. Flushed the system and now she runs cool as could be.

My sons stock 99, 140,000 miles, his daily driver, has mild cooling issues, but nothing too major. Looks like PO used some stop leak. We've been flushing out the system, but I will probably change out the radiator and other components as part of regular maintenance.

My 95 trail rig, 81,000 miles, has been the typical XJ cooling headache. Started with temp creep on the highway, and in town. So after putting on the lift kit, lockers, gears, 31's, I decided to attack the cooling system. I ended up changing everything, and I do mean everything. I tried every fix that I read about or was recommended to me. I tried 3 different radiators, CSF, stock, and one other. I finally had the biggest, stupidest radiator custom made to get the most fluid capacity. Re-routed the trans to it's own cooler. Tried Hesco and stock water pump, high flow T-Stat housing, deleted the heater control valve, new muffler and cat, ZJ fan clutch and stock fan clutch. I've checked for exhaust manifold cracks. Checked the radiator fluid, checked the compression, checked for fluid in the oil, blah, blah, blah. No culprit anywhere that I could find. So I just put up with it. I just cycle my fan override switch on the trails, and that keeps the temps where I want them. That's how I choose to manage the problem for now.

That's been my experience with XJ's. I can't figure it out, and frankly, doesn't seem like anyone else has. Seems like your cooling system works, or it doesn't. All the dozens of vehicles I've owned over the years have never had a cooling issue. If they did, it was an obvious fix, and I've owned a variety of vehicles.

So my advice, throw some parts at it, do what you have to do to make it work for you. I've even read where people have done engine re-builds over this issue. But I have no evidence of anyone saying "this" is the root problem. Yes it can sometimes be obvious and changing a few parts work, or it can be a major headache. Everyone seems to have different results. It's just baffling how so many people can have these problems without a clear solution. I'm at a loss to figure it out.

JMHO
 
Wow. Really great info guys. And I see why other threads are so inconclusive.

I'm going to throw some parts at it and see what I can do. I'll report back once I have something satisfactory to add.
 
The root cause is typically lack of regular preventative maintenance. The XJ cooling system is slightly undersized, but properly maintained it does the job.

To fix cooling system problems, one has to have a correct diagnosis. Throwing random parts at an undiagnosed problem often ends up with ineffective results. There is no one single faulty part causing XX% of cooling problems.

I do not consider a complete overhaul for a poorly functioning cooling system, with all parts replaced, as excessive.
 
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I have seen the lower hose collapse when hot and at high flow situations. The original hose had a "spring" inside to keep this from happening. I hear they are hard to find anymore.

Do not raise the back of the hood to get better airflow. It actually makes things worse. Go with a hood vent if you are going that direction.

I pull a trailer so I added an external transmission cooler. It seemed to help.

Make sure your fan clutch is good and you have a shroud around your fan. You should also have an aux fan. Add a manual switch so you can run it before it gets hot.
 
Agreed about the raising the back of the hood! I tried it in my 01 and it helped greatly when I was going box to box in town but once I got on the highway it acted like cowl induction and reduced airflow, increased temp. Would work on a slow speed/trail only rig, but not on anything that sees more than 20 mph.
 
I have seen the lower hose collapse when hot and at high flow situations. The original hose had a "spring" inside to keep this from happening. I hear they are hard to find anymore.

Do not raise the back of the hood to get better airflow. It actually makes things worse. Go with a hood vent if you are going that direction.

I pull a trailer so I added an external transmission cooler. It seemed to help.

Make sure your fan clutch is good and you have a shroud around your fan. You should also have an aux fan. Add a manual switch so you can run it before it gets hot.

And where would you place the hood vents? I have seen some placed forward, just behind the radiator. Jeep OEM hood vents come to mind. Others are at the back of the hood.
 
Hood vents help with keeping the engine cooler, they do not solve overheating issues.

The front corners of the hood is the most effective place for hood vents, but since low speeds are when the underhood temperatures rise the most, anywhere they will fit will help. Locating hood vents is somewhat limited due to the inner hood reinforcements on the underside.

There are tons of old hood vent threads to dig thru. >>> https://www.naxja.org/forum/showthread.php?t=1066309



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Just so you know I've seen parts be bad right out of the box. I got a brand new OEM Mopar radiator cap. The return plunger was bad out of the box. Allowed coolant to bypass the cap into the overflow bottle. Same things for thermostats. I've had them fail out of the box in both directions stuck closed and open.

Resist the urge to run lower than stock thermostats. Running an engine too cool is almost as bad as running it too hot. You get worse fuel mileage and significantly increased cylinder bore wear.

When it overheats as you describe does it only do it at speed, or at idle/low speed?
 
Hood vents help with keeping the engine cooler, they do not solve overheating issues.

The front corners of the hood is the most effective place for hood vents, but since low speeds are when the underhood temperatures rise the most, anywhere they will fit will help. Locating hood vents is somewhat limited due to the inner hood reinforcements on the underside.

There are tons of old hood vent threads to dig thru. >>> https://www.naxja.org/forum/showthread.php?t=1066309



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I have been following that thread for years. Living in Florida, the summer temperature could be brutal under the hood of the XJ. I have a set of Genright Off Road louvers for several months that I have yet to install. I want to place them where they will be most useful at highway speed. I am leaning towards the location shown in the picture you posted.
 
When it overheats as you describe does it only do it at speed, or at idle/low speed?

It overheats at low speed and at idle. It was particularly doing it under load and/or with the A/C on. Once I let it idle for a while with the heater on (which is weak despite attempts to flush) and hood open and it didn't overheat under those conditions. I then closed the hood and turned the A/C on and it overheated. The engine bay was scorching with the hood latch too hot to touch.

It should be noted that all of my experiences save for the one I just described were prior to doing the head gasket and new radiator. My mechanic was also able to replicate the overheating after the aforementioned work but I'm not sure exactly the conditions he saw it at. They're seeing the same thing as me where it stays at 210, creeps to 220 then suddenly jumps up and pegs the needle. Before the radiator was replaced it would also boil over even after a new cap. With the new radiator it does not (cap is still 16lb).

To recap, the issues that have been ruled out or parts that have been replaced are -
  • Head gasket
  • Insufficient burping
  • Water pump
  • Fan clutch
  • Thermostat
  • Radiator / radiator cap

I'm picking up the Jeep today. As much as I'd like to meticulously troubleshoot I don't want to risk a head gasket issue again. So I'm throwing the kitchen sink at it.

Because we seemed to have ruled out air bubbles or air entering the system the two theories I'm running with are (1) system is no longer capable of cooling sufficiently due to lack of care on part of PO (2) bad sensor combined with gradual overheat. I'm immediately throwing a ZJ fan clutch, lower rad hose, fan override switch and second new sensor at it. If there's no spring I'll pull one from the boneyard. I'm installing a high flow t-stat housing and 180* stat (temporarily) once they arrive. I'll go to a proper stant stat after I'm confident but want to give it every opportunity to stay cool. Then it's on to hood vents and new aux fan. I opted for some situated further back but after reading about cowl induction I may re-think that. If anyone has thoughts on those let me know. And if anyone can think of other high value mods I'm omitting I'll include those as well.

In terms of the wisdom of throwing the kitchen sink at it, my thought is that I don't mind having a more capable cooling system any way. If none of this works I at least will have an upgraded system when I eventually track down the problem. And if I have every mod with it's salt we know the problem is something more bizarre.
 
Well, the sudden jump is from the water flashing to steam. but you probably knew that.

If the system only has water in it (no antifreeze), & the system is holding 16 lbs of pressure....then it should not flash to steam until 252 deg.....if it only holds 8 lbs, then 233, and 4 lbs is 225.

With antifreeze at 50%, then 16 lbs jumps to 267 deg, 8 lbs is 248, 4 lbs is 236. ( https://durathermfluids.com/pdf/techpapers/pressure-boiling-point.pdf )

So, based on how you say yours is acting, it sounds like it isn't holding pressure, new cap or not.

One other thing to consider, the gauge may not be reading correctly, so ya need to verify that via IR or use a different gage.



If you replace the gauge sensor (back of the head by the firewall), be forewarned....Jeep no longer sells it, and all the aftermarket ones are a 14mm hex.....factory was 13mm.....and at least on mine, the 14mm deep well, even a thinwall, will not fit due to the lip on the valve cover. I literally had to use a die grinder to remove part of the valve cover lip to be able to put the new on in.

Also, the autozone sensors TU236 (at least mine did, and others have posted the same) seem to read 30 deg high. I returned that one and am using one from NAPA, but it also seems to read high...but have yet to verify how much (thinking it is in the 10-15 deg range).



and by the way....most cooling system mods aren't worth their salt........they just deplete your wallet.

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Newly installed does not mean installed correctly, or not failed again. You should look at the frost plugs for leakage and to the head gasket for leaking super heated exhaust gases to the coolant.
 
Updates, new theory and a little more color on the situation.

I touched base with my mechanic. He's skeptical it's the freeze plugs because he didn't see any leaks when he did the head gasket. He also told me that when he pressure tests the system it holds pressure fine. I wouldn't discount it entirely due to the fact that he wasn't directly looking for issues with them. But I'm not ready to tear up the engine bay to look at the freeze plugs. Have to keep in mind that I currently am working on this on the street (why so much is getting done by my mechanic). I'm moving to a place with a garage within a month so if it drags on I'll have greater ability to do things myself. He's also convinced the lower hose is fine so getting a spring from the boneyard is going slightly further down my list of things to try. Side note: any good threads on workarounds if I can't find one?

I screwed up because I thought my IR gun was in the car and apparently it's lost. However, I induced the issue again. I had to let her idle for about 30 minutes in 85* weather here in Denver (unusually cool :/) cycling the a/c on and off. Again it was when the truck touched a little over 220 that it suddenly jumped up, though this time the needle stopped a little shy of full blown overheating. Did not boil over. Hood latch was scorching hot and required a towel to open. I noticed the e-fan WAS NOT running (though it does come on with the A/C).

That little tidbit makes me think there's another possible theory here: the Jeep is actually gradually overheating due to the e-fan and the gauge sensor is malfunctioning. This would explain why it would jump both when the radiator boiled over and now. Under this theory it was previously overheating due to a secondary reason like the head gasket or bad cap. Or the griffin radiator just gives it more leeway now. The gauge has an equally long lag but previously it went to full overheat more quickly. Now it is taking longer and the gauge catches up before it can boil over or fully peg the needle. I assumed it was still pegging the needle but I just wasn't looking closely enough. Maybe these sensors are super prone to failure and because they're difficult to replace due to direct replacements no longer being available people never fully fix the issue?

The ZJ clutch didn't work out because of a foul up with the part numbers. I got the max cool which obviously didn't fit. But that's probably a blessing in disguise. The game plan at this point is to wire up a manual switch for the e-fan. See if the sudden increase can be induced even with it running. If not, see if it will overheat without the fan running at all. That would address the overheating itself. Then put in a new gauge sensor, attempt to induce the issue and see if it's a gradual or sudden increase. Hopefully it will be gradual. That would be a satisfactory resolution of the issue for me. If the gauge still shoots up, back to the drawing board and throw all the mods at it.
 
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