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Strange Overheating Issue

Slimer

NAXJA Forum User
Location
Tempe, AZ
Okay, I have read every thread I can find on the XJ cooling system and I am still stumped.

My new to me, 1997 XJ does the following: It runs great around town and 95% of the time on the freeway with the temp guage at around the 210 mark. But sometimes, usually when under load the temp needle jumps just to first line of the red zone on the guage and the check guages light comes on. I can either pull over or keep going and the guage stays right at the first part of the red zone on the guage for approximately 40 - 60 seconds and then jumps immediately back to the middle of the guage at 210 or so. It will keep repeating this cycle until I get off the freeway. The system does not boil over and the engine does not change the way it runs (it runs good).

- I am not using any coolant.
- I have a CSF Radiator (the sticker on the bottom says J16825310)
- I have a Champion Radiator Cap
- Coolant is Clean
- Lower Radiator Hose as the spring in it.
- All hoses look good are probably new within the last year.
- The Coolant in the fill bottle doesn't change levels.
- The Coolant looks to be 50/50.

What I have done so far:
- I have looked over the entire system for leaks and found none.
- I just replaced the Champion Radiator Cap with a Mopar Part #52079880AA.

I haven't tested the system with the new radiator cap yet, but will do so tonight. If I still have a problem I will try replacing the thermostat. I am suspecting the thermostat due to the strange cycling issue. When I do the thermostat I will also try find an incline and run the engine without the cap and with the rear temperature sensor loose in order to evacuate any air in the system. What else should I do? Am I on the right track? Any help would be greatly appreciated.

18953165_1518575831526171_6026724879894654487_o.jpg
 
I chased down my cooling gremlins for 2 years. Went through several flushes, backflushes, and ended up replacing every component of the cooling system. After all that, my XJ still wasn't cooling as well as I wanted; the magic bullet ended up being hood vents. Turns out the XJs engine compartment is like a freaking oven in the way it traps heat. Hood vents are great way to give that heat somewhere to escape. I went with the Daystar XJ hood vents. Not too expensive, great quality, USA made, look fantastic, and easy-ish to install.
 
Doesn't sound to strange. You are on the correct track; sounds like your thermostat is acting up and closing at random. I read that you haven't changed it yet but you will. I would change it and recheck it and let us know how it does. I would NOT DO ANYTHING else to the cooling system until a known good thermostat is in there.
 
After changing the radiator cap it still does the same thing, but less frequently.

I will change the thermostat tonight. I will use Mopar Part #52028186AC with the gasket Part #53020547AC.

I thought this was strange because of the way the gauge was acting. I have never seen a heat gauge make such erratic jumps back and forth without covering any temperature in the middle. Since it is jumping back and forth I am assuming it to be the thermostat.

I know that the previous owner owned the rig since it was new and had done lots and lots stuff to the cooling system. He mentioned that he had tried aluminum radiators before, but they didn't last and that he preferred copper and brass. He also said he tried the three electric fan setup and said that it didn't work so he sent it back. He also said that the stock fan setup worked the best for him.
 
Buy an IR thermometer and take a reading off the thermostat housing while the gauge is reading in the red zone. That should give you an idea of how accurate the gauge is.
 
After changing the radiator cap it still does the same thing, but less frequently.

I will change the thermostat tonight. I will use Mopar Part #52028186AC with the gasket Part #53020547AC.

I thought this was strange because of the way the gauge was acting. I have never seen a heat gauge make such erratic jumps back and forth without covering any temperature in the middle. Since it is jumping back and forth I am assuming it to be the thermostat.

I know that the previous owner owned the rig since it was new and had done lots and lots stuff to the cooling system. He mentioned that he had tried aluminum radiators before, but they didn't last and that he preferred copper and brass. He also said he tried the three electric fan setup and said that it didn't work so he sent it back. He also said that the stock fan setup worked the best for him.

Mopar 83501426AD is the thermostat and gasket and may be a little cheaper.
 
Buy an IR thermometer and take a reading off the thermostat housing while the gauge is reading in the red zone. That should give you an idea of how accurate the gauge is.

You can also pull into an Advance and get their scan tool and see what the coolant sensor at the computer is saying.
 
Could be an air bubble getting trapped near the sensor. Mine did that. I put an in line fill in the upper hose and it's gone. Make sure you bleed the system with the heater on full. You can also drill a small hole in the thermostat to aid in bleeding
 
Before I spent a ton of money, I would inspect/clean/lubricate all the connections(including the cluster bus)!
 
Before I spent a ton of money, I would inspect/clean/lubricate all the connections(including the cluster bus)!

Which connections? I see that you are in Phoenix. I am in Tempe! Does your rig run without overheating in yesterday's 119 degree heat?

I will do the thermostat tonight and my Napier Hood Vents come on Monday.
 
Which connections? I see that you are in Phoenix. I am in Tempe! Does your rig run without overheating in yesterday's 119 degree heat?

Any points in between the sensors, the PCM, and the instrument cluster. For the last 17yrs here, I've not had any issues(except a 0331 tradition)!
 
Bluetooth obd2 scanner you can monitor the tenps while you drive

Don't suppose you have one in mind that will sync up with Android products, and can be left plugged in during normal ops?

I'd like to have a HUD sort of arrangement for my son's 97.
 
Thanks very much!
 
Don't suppose you have one in mind that will sync up with Android products, and can be left plugged in during normal ops?

I'd like to have a HUD sort of arrangement for my son's 97.

I am using Automatic on all my vehicles. I just ordered one for the XJ.
 
Yahoo! I replaced the thermostat last night and found an aftermarket thermostat without the little air hole at the top. I replaced it with Mopar Part #52028186AC with the gasket Part #53020547AC put it all back together and took it for a test run!

I can now run 100-120 with AC on full blast and not overheat in the Arizona summer heat! I will keep testing it out this weekend and let you know how it goes. On Monday I am going to cut the hood install the Napier Hood Vents. Now I just have to get a new Speedo Cluster and switch to Miles Per Hour!
HEAT.jpg
 
Why do you have a metric cluster?
 
I am using Automatic on all my vehicles. I just ordered one for the XJ.

Automatic what? Automatic OBD II doesn't show anything in google....
 
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