Sloerolla

Hi all!

Lately my motor has been heating up past 210 when I am in a long line at In N Out. I jumped the aux fan and it works. The other day I was coming back across the border from Mexico and my motor got hot and didn't cool down. Yesterday I was in the drive thru and it got warm but cooled down. Am I to suspect a fickle temp sensor? I replaced the entire cooling system less than a year ago save the temp sensors. Oh.. 96 XJ 4.0. AW4 231. Any Ideas or advice? Thanks!!

tjwalker

To start with, you should verify your actual temp by pointing a laser thermometer directly at the thermostat housing. These tools are very inexpensive, widely available and every XJ owner should have one.

The sensor is a possibility but higher on the suspect list I think would be the fan clutch. Also, is your cooling fan shroud intact? Another important but sometimes overlooked part.

Did you replace the radiator "cap" when you did your cooling system?

Sloerolla

Yes I did, and the fan clutch. I eliminated the HCV, replaced the pump, thermostat and housing, every hose, and finally the radiator which seemed to fix the overheating issue I was having at the time. Looks like I will be getting a temp gun when the wallet says it's ok. Thanks! Oh.. and yes the shroud is intact.. I didn't even cut it to make it easier to remove

tjwalker

Yup, time to verify the true coolant temperature so that you don't end up chasing your tail!

I've seen infrared laser thermometers for sale as low as $10, but I would not choose the cheapest one for reliability and longevity reasons. Ebay, Amazon, Walmart, any parts store or hardware store, everybody carries these now. Nice tool to have on hand; I use mine for troubleshooting cooling systems, air conditioning, predicting house and auto electrical problems (look for higher temps than expected on all things electrical as high heat = future fail or even possible fire hazard).

If your actual coolant temps are lower than what you are seeing on your dash gauge, then it's time to start with swapping out the coolant temp sensor on the thermostat and if that doesn't resolve it, the problem is likely in the gauge itself. If the temps truly are high, then we will need to revisit it.

Good luck and keep us updated!

Sloerolla

Thanks!! Will do, but it may be a day or two. Thanks again!

cruiser54

Follow TJ's advice. Ever replace the radiator cap?

Sloerolla

yes that was the first thing I did cause it was the cheapest. I just relocated to San Francisco and I'm thinking the ambient temperature up here might play havoc with me trying to get it to heat up when idling. But I will get a temp gun in a day or so and see if I can ascertain anything significant. Thanks Cruiser, it's nice to be seen by the big guy!

cruiser54

A factory thermostat, although expensive, is all I use anymore. Heats up quickly and stays stable at 195*.
In 20* weather, I have heat in less than 2 miles of driving without warming up the Jeeps.

MattAlive

I'm having a temperature issue with my XJ, and what I've found may be of some help to you. My temp gauge started working sporadically and seemed like it was reading a bit lower than it should. Everything ran fine, no over-heating and the vents always blow hot air. I found some topics about replacing the temp sending unit and the coolant temp sensor. On some Jeeps the temp sensor is a separate unit located on the driver's side on the very back of the head by the windshield. On my Jeep, 2000 XJ, they switched to only 1 unit which controls it all, and it's just the one located on the t-stat housing. I replaced it last night and my temp gauge works, but it reads slightly lower than it should still. I'm going to replace again with the more expensive Mopar coolant sensor, as I read that anything but can give you poor results. I hope it works!

Sloerolla

Thanks!! I plan on getting a temp gun today and checking the validity of my sensor. Is there a relay that may be bad if the sensor and the gauge are working that would and the fan was not activating when the temp got high enough to need the extra air?

MattAlive

I'm not sure about any other relay in the system that you could check. In my digging I only found info about the two sensors, temp sensor to the dash gauge, located at back of head, and coolant temp sensor on the thermostat housing. What year is your Jeep? If you have both units, you might have to try replacing them both. But as I mentioned, my 2000 only has one unit which is the coolant temp sensor. I should be getting the more expensive Mopar sensor tomorrow and I'm hoping this takes care of my issue. The coolant temp sensor also controls other variables such as air/gas mix and I'm assuming the fan as well, while the temp sensor is only your dash reading. I've been chasing this mystery of super poor gas mileage on my Jeep as well, so I'm really hoping this Mopar sensor will take care of it!

PatHenry

On a 96 you'll have the temp sending unit at the back of the head - NOT in the thermostat. The one in the thermostat is the Coolant temp sensor.

If the actual temp matches the gauge, I'd still suspect a fan clutch. It seems pretty hit or miss with many of the aftermarket part brands, so even though you changed it it's still possible that the new one has failed.

Also if your radiator was a culprit last year, did you do a thorough flush of the block? If no, I'd do one now. The same crap that could have blocked up the radiator may be restricting flow in your engine.

PatHenry

Your aux fan turns on at something around 220, or whenever the A/C is on. The CTS triggers the fan at 220-ish. You can test the fan operation by turning the engine on and then pulling the connector off the CTS - the aux fan should kick on.
The sending unit at the back of the head ONLY deals with the gauge, everything else is the CTS.