Overheating/running hot...

Vertical rectangle? I run GenRight units on my hood and they work well. Mine are mounted 6" back from the front end of the hood and inboard from the fender about 6", following the raised edge of the hood. This allows the airflow to enter through the radiator and exit out the vents at low and high speeds.
https://genright.com/products/hood-louver-set-2pc-long-black.html

XJ_NorCal said:

I looked into Napa fan clutches and I couldn't find a Premium option.

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I have a new, in the box, Napa fan clutch.
It's identical to a standard-duty Hayden it's all that Napa carries anymore.

XJEEPER said:

Vertical rectangle? I run GenRight units on my hood and they work well. Mine are mounted 6" back from the front end of the hood and inboard from the fender about 6", following the raised edge of the hood. This allows the airflow to enter through the radiator and exit out the vents at low and high speeds.
https://genright.com/products/hood-louver-set-2pc-long-black.html

Click to expand...

Yes, that is the style I've been considering. Your setup is right above the battery and PDC on the passenger side. You haven't had electrical issues? do you have a photo of this setup? Just curious how it looks.

@xj_norcal were you able to diagnose your overheating issue? I have the identical problem and I think I have solved it.

ramathorn said:

@xj_norcal were you able to diagnose your overheating issue? I have the identical problem and I think I have solved it.

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I have not. Took the Jeep out this past weekend and it was running pretty hot again. What did you do?

Without success, I replaced:
Fan clutch
Thermostat (180 deg just to rule it out)
Water pump
Rad hoses
Heater hoses
Coolant (it is perfectly clean now)
ECT sensor
Radiator cap

Parts that are good:
Fan shroud
Electronic fan (switches on about 218 it seems)

Tests that were done:
Radiator pressure test (16 psi) - Passed
Radiator backflush - Clear
Thermostat test - Hoses are hot
Fan clutch resistance - Stiff (good)
Block test (engine cold) - Passed
Compression test (engine cold) - Passed
Block test (engine hot) - FAILED
Compression test (engine hot) - not completed yet

See below for the failed block test, it only failed this test once the engine was clearly overheating/boiling over. (F!*%$ing sucked to test it while it's blowing boiling water at you). Nevertheless, see how the fluid clearly has turned yellow, indicating there was exhaust in the coolant:



One theory is that once the engine gets really hot, the metal warps slightly and opens either a crack or head gasket into the coolant. This isn't a 100% confirmation, but I saw one other post identical to yours on a forum and he said it was a cracked head (but that was an 0331 head, unlike ours).

A hot compression test is something I will try next, but haven't done it yet.

PLEASE DO THE TESTS BEFORE SWAPPING PARTS, optimism will NOT solve a blown head gasket.

ramathorn said:

Without success, I replaced:
Fan clutch
Thermostat (180 deg just to rule it out)
Water pump
Rad hoses
Heater hoses
Coolant (it is perfectly clean now)
ECT sensor
Radiator cap

Parts that are good:
Fan shroud
Electronic fan (switches on about 218 it seems)

Tests that were done:
Radiator pressure test (16 psi) - Passed
Radiator backflush - Clear
Thermostat test - Hoses are hot
Fan clutch resistance - Stiff (good)
Block test (engine cold) - Passed
Compression test (engine cold) - Passed
Block test (engine hot) - FAILED
Compression test (engine hot) - not completed yet

See below for the failed block test, it only failed this test once the engine was clearly overheating/boiling over. (F!*%$ing sucked to test it while it's blowing boiling water at you). Nevertheless, see how the fluid clearly has turned yellow, indicating there was exhaust in the coolant:

One theory is that once the engine gets really hot, the metal warps slightly and opens either a crack or head gasket into the coolant. This isn't a 100% confirmation, but I saw one other post identical to yours on a forum and he said it was a cracked head (but that was an 0331 head, unlike ours).

A hot compression test is something I will try next, but haven't done it yet.

PLEASE DO THE TESTS BEFORE SWAPPING PARTS, optimism will NOT solve a blown head gasket.

Click to expand...

My XJ doesn't run hot when idling with A/C on. It runs hot when driving 65+ with A/C on. My "check gauges" light came on twice for a total of less than 30 seconds and immediately dropped after I turned my heater on. I've driven it 5+ hours in 100+ degree weather (including hill climbs) since the check gauges issue and it still hasn't overheated (no"check gauges" light). It runs hotter than I would like but I'm not convinced I have a blown head gasket.

First off, the statement was that the temp dropped 40 degrees in 10 seconds. It is impossible for the coolant to change that much in that amount of time. I'm not saying the gauge didn't reflect that or that the sensor didn't see that much change. The only way that amount of change happens is if you have an air bubble. If the air is around the sensor, the localized block temp will cause the sensor to read that high. The reason the temp drops that much is that it then gets hit with the coolant, which is much lower.

If the coolant was actually 250, you would have been boiling over, pressure cap or not.

What you describe is a classic air bubble reaction. Burp the system. Over time, air bubbles have a way of working themselves, but sometimes they can be very persistent. Many people buy a thermostat with a small hole in the plate and some people actually drill a hole. The purpose of the hole is to facilitate the air bubble working its way out of the head.

On a renix, it is easy to burp. Point the vehicle down hill and loosen the temp sensor on the rear of the head and let the air out.

The other way is to buy the fancy funnel that replaces the radiator cap and "over fill the radiator when the rig is facing uphill and start the engine and let it warm up.

Having said all of that, an air bubble can be caused by a cracked head or a bad head gasket as well. No amount of burping will keep it from coming back.