Strange Overheating Issue

[Boss Cherokee]

Even if it was a fuel lean issue, I cannot believe the gauge would jump/skip immediately as you have described. The lean issue would increase temp slowly the chambers and pistons heat would increase and as the load or lean out would increase. Again that is according to your statement that the gauge jumps over! That seems to be a variance in sensor or gauge resistance (faulty, fatigued). It could be alternator spike but without having temps from water neck ect... we can guess all we want!
As I said earlier and others have stated as well.
Get an IR gun and check both sides of the thermostat then check radiator outlets to start. I have a 4wd Ford van and I made a mistake hooking up the extra battery while I had the ignition on, I know, STUPID, and now my Diesel gauge will sometimes show full when it's not. I shut off the 7.3 motor and start it again and it's fine, go figure????

 

[Slimer]

First, I ordered a infrared thermometer from Amazon tonight. Second, I did a leak-down and compression test with the following results:

------LD-- C-- W
#1 - 5% 151 165
#2 - 5% 155 170
#3 - 6% 154 169
#4 - 5% 155 164
#5 - 7% 152 169
#6 - 6% 151 170

and I went out drove the snot out of until it overheated. At 75 MPH going up a small hill getting the transmission to kick down it finally overheated. Here is the video, you can skip to about the 1:20 mark. Remember that my gauge cluster is in metric. The previous owner stated that it has always ran at the "105" mark and that is where it ran on my way from Colorado Springs all the way to Arizona, going mostly 65-75 MPH without overheating.

https://youtu.be/5guiyEPFnnc

After it beeps and the Check Gauges light goes on I take my foot off the gas and coast for about 20 seconds and the tempature drops back down to normal. It stayed normal until I got back home going 65 MPH.

 

[David_Bricker]

(We are going to assume you don't have freezing temperatures to worry about- I'm unfamiliar with your region of AZ at this time of year).

Bwahahaha. Phoenix hit 122 last week. Not a lot of chance of freezing temps, but good on you to add the caution. Mesa is a suburb of Phoenix. I'm currently in Tucson and dying.

Fan clutch - get the ZJ standard duty (not extreme or heavy duty) from a 96-98-ish 4.0L ZJ. It will fit. It will be noisy. It may impact your mileage. It will be the best fan clutch for cooling. The Napa number I have for that clutch is NAPA #272310. The extreme duty ZJ fan clutch, which will likely be an interference fit with your radiator is Hayden #2796.

David Bricker / SYR - TUS

 

[TRAILREADYXJ]

and I went out drove the snot out of until it overheated. At 75 MPH going up a small hill getting the transmission to kick down it finally overheated. Here is the video, you can skip to about the 1:20 mark. Remember that my gauge cluster is in metric. The previous owner stated that it has always ran at the "105" mark and that is where it ran on my way from Colorado Springs all the way to Arizona, going mostly 65-75 MPH without overheating.

https://youtu.be/5guiyEPFnnc

After it beeps and the Check Gauges light goes on I take my foot off the gas and coast for about 20 seconds and the tempature drops back down to normal. It stayed normal until I got back home going 65 MPH.

With how fast that gauge is jumping this HAS to be some kind of electrical gremlin. Engine temps simply cannot change that fast!!!

As mentioned there is no point going into possible overheating causes until you know what temps you are actually running. See what your thermometer says when it comes in and I'd bet you aren't running that hot and it's something in the PCM, shorted wire somewhere, defective sending unit, etc... Install an aftermarket gauge for peace of mind if you'd like. Chrysler electronics suck and often have little gremlins like this. A loose ground or intermittent short somewhere can easily cause something like this. On TJs the wiring harness is known to rub bolts on the backside of the valve cover causing electrical issues, so something like this could easily be the case here. It can be hard to track down, but make sure you diagnose the real problem so you can focus on that instead of trusting 20 year old gauges!!!

 

[burntkat]

OK, here's what I'd do with a suspected electrical gremlin:

Go get an inexpensive mechanical temp gauge. Plumb it into the motor, literally anywhere you can. If necessary, use a tee. I can't tell you where off the top of my head, but there pretty much HAS to be an unused plug somewhere in the water jacket.

Plumb that in, install temporarily. I'd even duct tape it to the windshield if need be.

Go reproduce this issue. When the electrical gauge freaks out, see what the mechanical says.

While it's true that there will be temperature variances in the engine dependant upon where you're reading them, if you're reading in the engine itself there won't be a huge swing in coolant temp in one location without an affect in another location. IE: if you're sampling at the thermo housing and at the head, there will be similar swings in both.

If you don't see a swing in the mechanical, the factory gauge is a liar. Most likely a bad ground in the cluster, though it could be thousands of other things, to include a bad run of sensors (it's happened before).

For S&Gs, have you tried removing the thermostat completely and taking this same trip? I wouldn't take the trip right off the bat after removing the thermo- it's entirely possible that you might have too much flow through the radiator, not enough dwell time in the radiator to do its thing.

I've even seen situations in the past where you have to *restrict* flow through the radiator in order to get better cooling. In fact, an Aussie had that specific experience... in an XJ:
http://jeep-xj.info/HowtoRadiatorRestrictor.htm

EDIT: just something to note here: His first sentence: "I was having trouble with keeping a stable engine temperature. Was not overheating but the temperature swung down from 195*F to 160*F every 30 seconds!"

Hmmm.. seems familiar..... Gojeep is a good egg, I believe he's a member here, in fact. You can seldom go wrong emulating the Aussies, where a broken vehicle may mean you're well and truly FUBAR.

 

[dan1977p]

I am running 33's with 4.56's, an aux AT cooler, but am in Arizona where the average summer temperature is about 110 degrees!

Thanks for the replies everyone!!

Yeah, the areas in Utah where I was playing were the same.

 

[burntkat]

Wish I'd remembered that link before. I do believe that's going to be your answer.

Here's a cutting board, for cheap ($6):
https://smile.amazon.com/Winco-Cutt...498744513&sr=8-6&keywords=nylon+cutting+board

Grab a couple hole saws and see what happens.

The first question that will come to mind is "why would I need to do this if the factory didn't"? Well, the factory doesn't count on their average vehicle going to such extremes in climate. Also, lots of vehicles don't tell you what the temp is till it's a problem- my son's only has an idiot light for instance (I will address this soon with install of aftermarket gauges). .

For $6 (or thereabouts- Walmart has the nylon boards as well) and a little time , I'd try this before anything else. Install as mentioned in the link I left to GoJeep's site, then do a long idle test in the driveway. Passing that, go drive it. Passing that test, go take the route that gives you issues. I think you may be pleasantly surprised.

 

[dan1977p]

EDIT: just something to note here: His first sentence: "I was having trouble with keeping a stable engine temperature. Was not overheating but the temperature swung down from 195*F to 160*F every 30 seconds!"

Hmmm.. seems familiar..... Gojeep is a good egg, I believe he's a member here, in fact. You can seldom go wrong emulating the Aussies, where a broken vehicle may mean you're well and truly FUBAR.

I didn't see that at first either. For me it was the actual single pin connection for the temp sender on the head near the firewall, but I think that sender was taken out before 97. I'd suspect a wire with worn insulation or broken at a bend with the insulation still in tact somewhere along the line. Most likely culprit would be where it turns out of the plastic holder with the injector wires near the firewall. That's pretty common on XJs and I had to tape up my O2 sensor wires for the same reason.

 

[burntkat]

I didn't see that at first either. For me it was the actual single pin connection for the temp sender on the head near the firewall, but I think that sender was taken out before 97. I'd suspect a wire with worn insulation or broken at a bend with the insulation still in tact somewhere along the line. Most likely culprit would be where it turns out of the plastic holder with the injector wires near the firewall. That's pretty common on XJs and I had to tape up my O2 sensor wires for the same reason.

Not sure what you're talking about. The thing I'm referencing has nothing to do with an electrical fault.

That could be an issue, yes, but I am really thinking the restrictor is going to be the solution here.

 

[Slimer]

Even if it was a fuel lean issue, I cannot believe the gauge would jump/skip immediately as you have described. The lean issue would increase temp slowly the chambers and pistons heat would increase and as the load or lean out would increase. Again that is according to your statement that the gauge jumps over! That seems to be a variance in sensor or gauge resistance (faulty, fatigued). It could be alternator spike but without having temps from water neck ect... we can guess all we want!
As I said earlier and others have stated as well.
Get an IR gun and check both sides of the thermostat then check radiator outlets to start. I have a 4wd Ford van and I made a mistake hooking up the extra battery while I had the ignition on, I know, STUPID, and now my Diesel gauge will sometimes show full when it's not. I shut off the 7.3 motor and start it again and it's fine, go figure????

Did you watch the video Boss Cherokee?

I will look for bad wiring and then the restricter if I don't find anything. I also want to switch to a regular gauge cluster instead of this metric one so maybe that will solve it too.

 

[burntkat]

Any news on this?

I should have a cutting board from Amazon waiting on me when I get home. Already have the holesaw and drill bit. If you like, I'd be happy to cut out one for you and ship it your way.

 

[Slimer]

Any news on this?

I should have a cutting board from Amazon waiting on me when I get home. Already have the holesaw and drill bit. If you like, I'd be happy to cut out one for you and ship it your way.

My Ace Hardware actually had some Delrin washers that fit perfectly. I tried several different interior hole sizes and all made the problem worse. I did check the thermostat housing with the thermo-gun and it is actually getting hot as the gauge says. The spread from the one side to the other is about 80 degrees until the thermostat opens and then it starts to equalize. When it overheats (check gauges light comes on) the temperature is 254 and stays there for about 120 seconds with the washer in and about 30 with the washer out.

I think I have either a bad head gasket or a cracked head that is leaking CO2 into the coolant only under load and then the system quickly belches it out when the thermostat opens. When it belches the CO2 out the system can cool again. It doesn't show with block tester, compression, or leak-down tests because the engine is not under load during those times. I am going to try to run it on a dyno today and see if we can see it happen.

 

[burntkat]

CO2? Not sure where it would get that....

Do a cooling system combustion products test when on the dyno. Can't hurt. You're not going to be driving and will need the hood up during the test, so being on a Dyno is a perfect place to do it. It will give you another data point to fix the issue.

 

[RCP Phx]

I still don't see that you used a scan tool to monitor what's happening in real time? What does your O2 sensor read? What does your LTFT and STFT read?

 

[Slimer]

All sensors read normal, fuel pressure, etc..

CO2 would come through the combustion chamber through a cracked head or a bad head gasket. Everything tests normal.

 

[burntkat]

All sensors read normal, fuel pressure, etc..

CO2 would come through the combustion chamber through a cracked head or a bad head gasket. Everything tests normal.

/believe you mean CO. Carbon MONoxide, not Carbon DIoxide??

 

[RCP Phx]

I still don't see that you used a scan tool to monitor what's happening in real time? What does your O2 sensor read? What does your LTFT and STFT read?

All sensors read normal, fuel pressure, etc..

CO2 would come through the combustion chamber through a cracked head or a bad head gasket. Everything tests normal.

I'm not talking about whether the sensors are good. I'm talking about the actual numbers by reported by the PCM! The voltage reported by the O2(0-1 volt) and the %'s being shown for STFT and LTFT!

 

[Slimer]

I lost my free dyno time until until Monday morning... bummer. Hurry up and wait longer. Basically, no one, anywhere has a clue what is wrong with it. I did take to a regular mechanic and he supposedly ran it on the "scope" and everything was normal, but he couldn't get it to overheat in his shop, only on the highway going up a hill or when running about 3,000 RPM.

I will try the dyno if I can actually get on it, otherwise I will probably take it to Hopper's in Tempe and let him have a crack at it. He's a Jeep guy. Other than that I don't know.

 

[burntkat]

Have we taken a look at the temps before/after the catcon? A plugged cat might give these symptoms..

 

[Slimer]

A plugged catalytic converter? How do I test for that? I doubt anyone has looked at that yet.