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  #31  
Old July 24th, 2020, 15:49
whatwave whatwave is offline
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Re: Sudden overheating, at a loss what to do next

So I'm fairly certain the overheating is not actually sudden. I now think these gauges aren't to be trusted. I just idled the truck for 40 minutes playing with the e-fan and comparing OBD readings to the gauge. Once the gauge hit 210 it was rock solid... despite Torque showing lots of fluctuation. Maybe Chrysler designed the gauge to move less so people wouldn't freak out? I think that should be the big takeaway for anyone reading this. The first thing you should do is watch the coolant temp via the OBDII port.

Second, I think there's a chance my problem has been solved. The last time I induced the issue I noticed the e-fan was not on when it overheated. I swapped out the sensor and now the e-fan turns on at 220 (OBD, not gauge) and does a pretty good job bringing down the temp. Moreover when I just kept the efan on manually it stays at 203* at idle in 80* weather. So keeping it on all the time is a viable option.

I have an appointment with a Jeep specific garage for a diagnosis. These guys are all booked out 3+ weeks so I'm going to keep it on the books for now but fingers crossed I'll be able to cancel it.
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  #32  
Old July 24th, 2020, 18:19
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TRCM TRCM is offline
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Re: Sudden overheating, at a loss what to do next

Try letting it idle in gear and see how it does......that will give you a better idea of if it will overheat in driving conditions.

My gauge reads within 5 deg of the actual temp of the thermostat housing, but the e-fan doesn't come on till 230 deg.
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  #33  
Old July 24th, 2020, 21:43
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 TRCM View Post
Try letting it idle in gear and see how it does......that will give you a better idea of if it will overheat in driving conditions.

My gauge reads within 5 deg of the actual temp of the thermostat housing, but the e-fan doesn't come on till 230 deg.
.
Great idea, thanks! I took her to the pharmacy with the same results. 203* as long as I was running the fan. But that's a short easy drive and it was coolish out. I'll try letting it idle in a forward gear during the heat of the day
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  #34  
Old July 25th, 2020, 05:25
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TRCM TRCM is offline
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Re: Sudden overheating, at a loss what to do next

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Originally Posted by whatwave View Post
.
Great idea, thanks! I took her to the pharmacy with the same results. 203* as long as I was running the fan. But that's a short easy drive and it was coolish out. I'll try letting it idle in a forward gear during the heat of the day
Just make sure you adjust the rear brakes 1st....then use the parking brake and a chock or 2 in front of the tires to stop it from moving (or ya could put it up on 4 jackstands...as long as they ain't the harbor freight kind).

I had to let mine idle for 29-30 min in gear with a heavy welding blanket blocking the grill on a 98 deg day to get it hot enough to kick on the e-fan (I do have the better 4 cyl fan clutch on mine and a 195 deg t-stat).

I also kept an eye on the t-stat housing temps and the head itself back by the sensor for the gauge) using my IR gun. That's how I found out the autozone temp gauge sensor (back of the head on my 96) was showing 30 deg high....and the current NAPA one is only 5 deg high.....

Checking things this way also lets you see how your gauge indication compares to actual temps.....and if it has a smooth swing or not.


The NAPA/Echlin sensor I am using seems to come up to temp way too fast (like as soon as you start the cold engine it comes off the 100 deg bottom line), but in the normal operating range of 185-235 (1st line either side of the center 210 line on the gauge face for a 96), it is pretty close.

T-stat housing temps are within 5 deg of what I'd say/guess the gauge is reading, and with no more lines than the gauge face has, it's hard to be very accurate.


I am going wire in a switch that lets me turn the fan on manually without messing with the PCM.,..just gotta get off my fat butt and do it. I plan on using a stock switch (rear defrost or maybe comfort/power) out of my parts jeep for this so it sort of looks factory.

Let us know what ya find out...may help someone else with the same or similar problem.........


.

Last edited by TRCM; July 25th, 2020 at 05:31.
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  #35  
Old July 25th, 2020, 08:05
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Re: Sudden overheating, at a loss what to do next

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Originally Posted by whatwave View Post
..... Maybe Chrysler designed the gauge to move less so people wouldn't freak out? I think that should be the big takeaway for anyone reading this.
The dashboard temperature displayed and the alternator voltage displayed are buffered by the PCM to prevent owner freak out. The gauges are not dependable for precise data display, but they are dependable for indicating normal functioning, and gross malfunctions.
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People are dumbfounded when I tell them I know how to change the spark plugs on a car.
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  #36  
Old July 26th, 2020, 09:45
whatwave whatwave is offline
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Re: Sudden overheating, at a loss what to do next

I attempted to induce the issue again idling about a half hour with the Jeep in forward gear. It doesn't overheat because the fan consistently kicks on about 220 (OBD).

I've noticed that there's a lag with the OBD temp readings. Revs and other parameters are real time but coolant temperature takes about 10 seconds to refresh. So if the gauge is pulling from that there's more shenanigans there.

I'm tempted to think the problem was combination of a faulty sensor that was causing the fan not to kick on and a lag in the gauge. The efan on manual keeping it at 203* lends more credence to that for me. From what I've seen I can buy a moderately quick increase showing up as a slight increase and then a very quick one on the gauge. Or possibly a faulty sensor in combination with the gauge buffer caused a weird output. That seems more likely to me than a loss of pressure or air pocket (rad not boiling over + all the work + pressure test being okay).

I've decided to keep the appointment for the diagnostic anyway due to the overheating PTSD I have at this point. I'm going to give her light around town duty until then and if the second garage gives her a clean bill of health I'll start wheeling.

Even if this isn't fixed, I take two lessons away so far. The first is verify the gauge with an IR temp gun and OBD. Possibly less pertinent in AMC versions due to the temp coming from a different place. Second, if you're going to start throwing parts at a problem do every cheap item all at once up front. I'm happy to have a fresh cooling system but if I could have opted for $50 in sensors, hoses, stat, etc I probably would have gone for that.
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  #37  
Old July 26th, 2020, 18:20
Evan03 Evan03 is offline
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Re: Sudden overheating, at a loss what to do next

We have to ask ourselves. Did the 4.0 over heat new from the factory 99% percent will answer no.
So when did this start 5miles from the factory or 120k
And why did it start? What has changed in time and miles what effect does water and minerals have on materials

I would not discount a head gasket on any motor that has persistent heating issues.

If radiator,heater core, tstat, pump yada everything is changed what does that leave? internal passages head gasket (again)?

Is the 4.0 sand cast?
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  #38  
Old July 28th, 2020, 20:03
whatwave whatwave is offline
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Re: Sudden overheating, at a loss what to do next

I couldn't resist the temptation and wound up taking her wheeling today. I was careful but it was still 100 miles and an elevation gain of 5,500 ft. Coolant never exceeded 210* (OBD reading). I think it's gtg.

The only things that changed from when I could get it to overheat while idling and now were the temp sensor and wiring the fan for a manual override. I'm pretty convinced it was a problem with the sensor not triggering the e-fan. I think the Jeep was overheating but not quite so suddenly.

One minor correction. The OBD temp reading does refresh in real time. However, it seems to be in celsius and in integers rather than continuous. I was seeing it go from 203 to 204.8 F and assumed it was refreshing weird. In reality it was just going from 95 to 96 C and that made it appear to be refreshing weird. Also possible that's just the app I'm using.
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  #39  
Old July 29th, 2020, 03:45
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Re: Sudden overheating, at a loss what to do next

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Originally Posted by whatwave View Post
I couldn't resist the temptation and wound up taking her wheeling today. I was careful but it was still 100 miles and an elevation gain of 5,500 ft. Coolant never exceeded 210* (OBD reading). I think it's gtg.

The only things that changed from when I could get it to overheat while idling and now were the temp sensor and wiring the fan for a manual override. I'm pretty convinced it was a problem with the sensor not triggering the e-fan. I think the Jeep was overheating but not quite so suddenly.

One minor correction. The OBD temp reading does refresh in real time. However, it seems to be in celsius and in integers rather than continuous. I was seeing it go from 203 to 204.8 F and assumed it was refreshing weird. In reality it was just going from 95 to 96 C and that made it appear to be refreshing weird. Also possible that's just the app I'm using.


Based on your posts, I checked the OBD readings on mine as well, and it acts the same way.....

My gauge also appears to indicate about 9-10 deg above the OBD reading, which would explain the gauge showing ~230 deg when the e-fan kicked on, but the IR temps were closer to 220 deg.
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  #40  
Old July 29th, 2020, 08:39
Rockwood Rockwood is offline
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Re: Sudden overheating, at a loss what to do next

Another thing to check is if the shrouds are on properly and sealed: I ended up adding a bunch of foam from cheap Harbor Freight anti-fatigue mats and some zip-ties to hold it to seal everything together. For example: there is a near 1" gap between the two fan shrouds, which means the mechanical fan is drawing air from the E-fan area when off (reducing airflow through the radiator) and the e-fan is likely drawing from the mechanical fan side when on. The bottom of both shrouds do not seal well against the radiator, especially around the steering box on the E-fan, and there are some definite gaps on top (sealed with split hose on the sheetmetal).

Hood vents helped reduce overall heatsoak under the hood for me. Still will burn your hands when popping the hood, but at least the hood latch doesn't burn, and there is a lot less heat blast under the vehicle and through the tunnel.

I also added a layer of foam car insulation to the interior to help the AC out. Now when it's 100*F out, I can run the AC on 1 or 2 and be comfortable, where before it was constant full blast. Floorboards no longer melt dropped gummy bears into the carpet, which is nice.

Thermostat: went to a 180*F thermostat. The ECU goes into closed loop at 183*F and the 180*F thermostat does not appear to fully open until 195*F or higher. The stock 192*F thermostat does not appear to fully open until 210*F. Coolant temps in 35*F weather still are above 190*F, but I'm in SoCal. Your mileage may vary.

Oxygen sensor: Make sure you DO NOT have a MIL for failed front O2 sensor. This will make the Jeep run pig rich and turn the exhaust manifold into a furnace.

ZJ fan clutch: helps a ton... But on the trail in low range sounds like a UPS truck. Expect continuous jabs from non-XJ owners.

Teralow 2LO kit: with lunchbox lockers front/rear, this was my favorite mod overall and helped a lot for cooling since I wasn't always loading the power steering system and fighting the lockers in every turn. This resulted in less load for the engine and cooler temps.

All of this was nice on the Shaver Lake area wheeling trip earlier this month, even with 9000' elevation and temps in the mid/upper 80s on the trail, no issues at all staying cool. Was also able to do most of the trails in 2LO, which added some fun challenge, but also wasn't kind to my rear tires.
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