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Strange Overheating Issue

Slimer said:
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
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120 in an XJ? You're a brave man....

EDIT: nevermind, that's KMH...
 
Green XJ Jeep said:
Nice.
Not sure why the little hole would cause overheating. Its there to help bleed air out of the system.
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The factory Mopar thermostats have a little hole at the top to help bleed air out of the pressurized side of the system. Overall, I think it was just a bad thermostat. I didn't find any junk lodged in it, I just think it was a cheap Chinese unit.

001.jpg

Do you see that little brass circle on the edge of the thermostat? It is the air bleeder. Some guys just drill a hole in the cheap thermostats that don't come with them. Everything that I read on the internet about the XJ said to use factory parts and not cheap aftermarket parts.
 
So do I.
 
Well, I have the problem solved on flat ground, but on the highway, heading up to the mountains, on a steep, long grade, and it does the same thing. Jumps from the middle of the gauge to the first line in the red and the check gauge light comes on. I pull over or even keep going and just get out of the gas and 30-60 later it pops back down to the middle of the gauge again.

Cutting the holes in the hood on Monday and installing the Napier vents. Any other suggestions? When I did the thermostat I can tell the water is fairly new. May a CO2 test for a bad head gasket or something?
 
OK, maybe I missed it but didnt you say your not using coolant? Water boils at 212* and thats where air bubbles are coming from which could be whats confusing your sensor. try adding coolant and bring the boiling temp up to 260* (f) and see what happens.
 
jimbar said:
OK, maybe I missed it but didnt you say your not using coolant? Water boils at 212* and thats where air bubbles are coming from which could be whats confusing your sensor. try adding coolant and bring the boiling temp up to 260* (f) and see what happens.
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I am running a Peak 50/50 in it. It has coolant, it just isn't "using" any, in other words, the coolant doesn't disappear.

I changed out the temp sensor today and no change.

Today, when I start it cold it just turns over for about 15-20 seconds before it actually starts. I think it is getting ready to kick-the-bucket. Not sure what else to do. Around town it runs great.
 
Any other suggestions? I have done the following:
1. Changed the radiator cap to a Mopar part.
2. Changed the thermostat to a Mopar part.
3. Purged the cooling system of all air (twice).
4. Changed out the coolant temperature sensor.
and the radiator and water pump are both fairly new.

Now it takes about 15-20 seconds to start when it is cold. I have no water in the oil and don't lose any coolant.

It just overheats under heavy load.
 
Way past time to run a hydrocarbons test in the coolant. Oreillys has the test kit as a rental tool. This will tell you quite a bit about the state of the engine. Also, do a compression test.
 
When you say heavy load what are you towing?

Have you checked your mechanical fan to make sure it isn't shot? If that is gone your jeep won't ever cool properly

If it's taking a while to crank that is going to something entirely different than a cooling issue.
 
Check your fuel pressure running it hard up hill. If the motor is leaning out it will run hot as well. Also check exhaust backpressure. Shouldn't be more than 6psi at high rpms.
 
smokeyyank said:
When you say heavy load what are you towing?

Have you checked your mechanical fan to make sure it isn't shot? If that is gone your jeep won't ever cool properly

If it's taking a while to crank that is going to something entirely different than a cooling issue.
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I am not towing anything, just going up a long, steep grade a couple miles long.
 
cwyman6 said:
Check your fuel pressure running it hard up hill. If the motor is leaning out it will run hot as well. Also check exhaust backpressure. Shouldn't be more than 6psi at high rpms.
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Thank You - cwyman6!

I am starting to think it might be fuel issue also. Sometimes when I start it stumbles and runs terrible. I turn it off and restart it and it runs fine again. This would explain the overheating, the hard start issue when it is cold, and the stumbling issue. The XJ came from Colorado and is now in Arizona. I bet it uses more fuel here in AZ since I am closer to sea-level and something is clogged so it can't get the fuel it needs under a high load. It was fine the entire way home from Colorado.
 
cwyman6 said:
Check your fuel pressure running it hard up hill. If the motor is leaning out it will run hot as well. Also check exhaust backpressure. Shouldn't be more than 6psi at high rpms.
Click to expand...

How does one measure backpressure?
 
Slimer said:
Thank You - cwyman6!

I am starting to think it might be fuel issue also. Sometimes when I start it stumbles and runs terrible. I turn it off and restart it and it runs fine again. This would explain the overheating, the hard start issue when it is cold, and the stumbling issue. The XJ came from Colorado and is now in Arizona. I bet it uses more fuel here in AZ since I am closer to sea-level and something is clogged so it can't get the fuel it needs under a high load. It was fine the entire way home from Colorado.
Click to expand...

First thing to look at would be the filter, in this case.
 
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