Does your Cherokee still have the factory 0331 head? The 2000 and 2001 XJs had them. They are notorious for cracking, even without running them hot.

 

I replaced the head when I got the Jeep. Can't remember the brand, but I'm pretty sure it was the brand that everyone recommended at the time.

Currently, XJ is not losing coolant or have coolant in the oil. Hoping that's not the issue. The last time I verified by having my oil analyzed after losing coolant from the reservoir.

 

I'm jealous. It was in the 20's today in MA with a high of 40 something.

 

haha This morning it was 49F.

Went for a short ride and got stuck behind some construction. The coolant Temp reached 223F and after there is fresh airflow the temp will go back down to 205F. rather quickly. Electric fan came on at 223F

wondering if it could be the AC DElco temp sensor that's not fast to send info to the AUX fan? I'm out of ideas at this point.







This is what the temp gauge looks like at 223F on the OBD2

 

I think that it could be by design that the gauge is slow to react. If it was a big problem for the coolant to spike to 223, there'd be no reason to put in a fan that kicked on at that temp, right?

Thinking back to my 2000 TJ with all the cooling issues I had (3x radiator replacement, 2x water pump (the last was on the side of the highway 500 miles from home)) the only time I had the gauge read slightly over 210 (when it was new and while working correctly it was rock steady at slightly under 210) was when I had a leak in the system. I couldn't figure it out until I grabbed a coolant pressure tool from Autozone (it's a loaner tool, so free with deposit) and put pressure on the system. When I did it was very obvious that I hadn't gotten the t-stat housing on tight enough (or didn't set the gasket). It didn't leak without pressure on it (maybe it did while driving), even when the engine was running at temp while idling. IIRC I could smell the antifreeze after driving and opening the hood, but it wasn't overwhelming.

I would definitely grab that tool and manually pressurize the system if you haven't tried that already. Again I'm just throwing ideas out there since this is such a baffling mystery.

Also, how old is your radiator cap? If you didn't replace it when you did the radiator/water pump or if it wasn't the proper OEM pressure, I'd definitely do that as well. I was surprised how much the pressure affected the coolant temp.

That's all I can think of myself.

 

I would suggest that you verify the accuracy of your temp sender with an IR thermometer at the thermostat housing. It could be that it's not actually hitting 223 degrees as the sender is reporting to OBDII.

In my experience, it's not normal for the temperature to reach 223 degrees in 49 degree ambient temps unless you're working it really hard and then idling hot for a long period of time. It's rare for mine to come on in 90 degree + temps unless I'm towing or crawling.

 

ambient temp has been 74F-76F




not sure why the video came out with fisheye lens. but here is a short video

CoolantVideo



OBD said 219-221 F and infrared was really HOT 225F-233F



weird because it started with the coolant temp being at 217F at the OBD reader and the infrared hovering at 205F...then it just got really hot, the electric fan came on as I was recording.

I'm thinking I'll let the coolant cool down and will install the OEM coolant sensor. At this point, I guess it won't hurt to try.



CoolantVideo

 

How long were you sitting stuck behind construction?

Thanks for the vid! I will review it when I get home.

 

The temp sensor is a variable resistor. That reading is interpreted by the PCM. The temperature value is sent over the CCD bus to various systems, including to your OBD2 bluetooth reader. What you are seeing there is the actual temperature read by the PCM.

The fan turns on when it gets a signal from the PCM. If the PCM is reading 223 but the fan is not turning on, you should probably check on that.

Thats because the gauge is a damned dirty liar

 

I stopped to dropped over a PKG at FedEx and when I came back and turned the Jeep ON, I idled for about 5 min. This is when I first saw 219F with AC ON.

Not even 200 yards into my drive, the temp drops to 210F. A couple of minutes later, 1/2 mile into the drive the congestion started to get worse. It was bumper to bumper for 8-10 min and right away the temp went to 223F. Got a clear


changed to the OEM coolant sensor and burped the system, no more bubbles coming out and a good 40min later. I still get 219F with AC ON and 214F with the AC OFF. I idled a good 15min and the temp never went down. Hood closed.

wondering if the compressor is causing excessive drag. It' relative new. 3-4 years old. Not many miles for sure. It's a Denso compressor, not a rebuilt.

 

thanks!

 

Ah, never mind what I've mentioned above... I wasn't considering A/C use since I'm in the Midwest. I don't think what you're experiencing is that odd for A/C use at a stand-still, but I can't really comment because I haven't used A/C in my XJ for years. The condenser dumps a lot of heat into the radiator.

 

Yeah, I can't figure out on what it could be. I suppose I'll test my oil for coolant to discard the cylinder head having an issue.

I have an oil test sample from my last oil change. It's been in the sample bottle for over 2 months, I am sure that it's probably not the best sample to get the oil tested in order to see if I am seeing coolant in the oil.


Can't remember what brand I used for the replacement (Clearwater Cylinder Heads, j&c enterprises or Alabama) but I know it was above $500

Another theory is that perhaps when I did the water pump & thermostat a year ago. I could have dropped something small into the engine and might have plugged up a coolant channel-just not sure at this point.

 

Did you replace the radiator cap? check the overflow tube for clogs?

 

It's a new Mopar cap that came with the new radiator.

No issues that I can see with the hose. Seems to be in good shape.