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  #16  
Old July 14th, 2020, 18:53
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techno1154 techno1154 is offline
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Re: Sudden overheating, at a loss what to do next

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Originally Posted by Tim_MN View Post
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



.
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.
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1996 XJ; 4.0L; AW4; NP231; SYE; D30 and D44; ECTED; 4.10 gears; 30X9.5 -15 BFG/AT/KO; 3" lift; Rusty's LCA; JKS ADJ UCA; Kevins ADJ Track bar; Drawtite Front Receiver; Dual Electric Fans; Dual Battaries.
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  #17  
Old July 15th, 2020, 09:41
whatwave whatwave is offline
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Re: Sudden overheating, at a loss what to do next

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Originally Posted by devildog0 View Post
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.
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  #18  
Old July 15th, 2020, 11:22
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TRCM TRCM is offline
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Re: Sudden overheating, at a loss what to do next

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/tech...ling-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.

.

Last edited by TRCM; July 15th, 2020 at 11:29.
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  #19  
Old July 15th, 2020, 14:41
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Re: Sudden overheating, at a loss what to do next

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.
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  #20  
Old July 17th, 2020, 08:06
whatwave whatwave is offline
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Re: Sudden overheating, at a loss what to do next

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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  #21  
Old July 17th, 2020, 08:14
whatwave whatwave is offline
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Re: Sudden overheating, at a loss what to do next

Other quick question for the gurus here. How bad of an idea would it be to try replacing the gauge sensor with a boneyard unit? I'm going to have difficulty modifying the valve cover gasket on the street. Issues I could see are (1) if I find a good one it doesn't last as long (2) possible that when they break they all malfunction in the same way.
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  #22  
Old July 17th, 2020, 10:16
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Re: Sudden overheating, at a loss what to do next

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Originally Posted by whatwave View Post
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. .
Ask for the 4cyl XJ fan clutch. Hayden P/N 2737. This helps prevent that screwup with the HD ZJ fan clutch. The mod should be called the 4CYL fan clutch mod instead of the ZJ fan clutch mod.
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  #23  
Old July 17th, 2020, 11:33
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Re: Sudden overheating, at a loss what to do next

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Originally Posted by devildog0 View Post
Ask for the 4cyl XJ fan clutch. Hayden P/N 2737. This helps prevent that screwup with the HD ZJ fan clutch. The mod should be called the 4CYL fan clutch mod instead of the ZJ fan clutch mod.
From what I've seen the HD 4 cyl fan clutch and the ZJ fan clutch are the same...

if his radiator (max cool) is too thick the new fan clutch may not work, no matter what you call it.
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  #24  
Old July 17th, 2020, 13:38
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Re: Sudden overheating, at a loss what to do next

The standard ZJ fan clutch and the 4cyl XJ fan clutch are the same but when you get the heavy/severe duty ZJ fan clutch it's a lot thicker than the 4cyl XJ one.

4cyl XJ fan Clutch


ZJ Severe Duty Fan Clutch. It doesn't even look like most places even list the "standard" fan clutch for the ZJ anymore and have nothing but severe duty ones listed.


I've actually got a 2737 sitting on my shelf now that I keep around for hot weather. I replaced it with a standard OEM clutch I scrounged up from one of the OEM parts houses and havent' felt the need to switch over this year.

And just for comparison a standard duty 4.0L XJ fan clutch. If you could see the front there is no heat sink on the front of these just a metal plate.
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  #25  
Old July 17th, 2020, 13:54
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Re: Sudden overheating, at a loss what to do next

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Originally Posted by devildog0 View Post
And just for comparison a standard duty 4.0L XJ fan clutch. If you could see the front there is no heat sink on the front of these just a metal plate.
That's what I just replaced on mine.....4 cyl version is much better................
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  #26  
Old July 17th, 2020, 13:57
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Re: Sudden overheating, at a loss what to do next

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Originally Posted by TRCM View Post
That's what I just replaced on mine.....4 cyl version is much better................
It's gotta be since the 4 cyl don't have the e-fan and the mech fan has to do all the work.
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  #27  
Old July 17th, 2020, 20:59
whatwave whatwave is offline
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Re: Sudden overheating, at a loss what to do next

I was just comparing all three of those at NAPA. I have the 4 cyl / standard ZJ in hand now.
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  #28  
Old July 18th, 2020, 10:01
whatwave whatwave is offline
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Re: Sudden overheating, at a loss what to do next

Is the OBD reading coming from the sensor on the thermostat housing or the one for the temp gauge? Wondering if I could use Torque to compare the two and see if there's a discrepancy.
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  #29  
Old July 18th, 2020, 12:47
whatwave whatwave is offline
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Re: Sudden overheating, at a loss what to do next

I found a small coolant leak around the thermostat housing. This seems like it has the potential to screw with things.
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  #30  
Old July 18th, 2020, 15:32
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Re: Sudden overheating, at a loss what to do next

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Is the OBD reading coming from the sensor on the thermostat housing or the one for the temp gauge? Wondering if I could use Torque to compare the two and see if there's a discrepancy.
OBD reading comes from thermostat housing coolant temp gauge. But since you're in a 97 you shouldn't have a head mounted temp sensor for your dash gauge. The gauge gets it's info from the computer which is from the tstat housing.
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