HELP! Just Bought an XJ - Overheating Issues

[NikVallens]

After lots of searching for a clean 2 door XJ, I found a great 98 XJ 4x4 with only 98k miles. I flew from Southern to Northern CA to pick it up and drive it the 400 miles home. I first stopped to get the oil changed and get a quick look from a mechanic who gave the thumbs up before driving home.

After 5-10 miles on the freeway at 70-80mph, the thermostat light came on and when I opened the hood, coolant was boiling out of the overflow reservoir. Looking at the service records, the usual culprits such as the water pump and thermostat were replaced 3.5 years ago but the Jeep has only been driven about 4k miles since then. Is it possible the Jeep sitting could cause a relatively new thermostat to freeze closed?

After letting the engine cool, I drove for 45 minutes on surface streets up to 55mph with no issues, but I am hesitant to drive home without getting to the bottom of the issue. The coolant seems to be in good shape, radiator fan operating properly, and no obvious leaks. With the water pump and thermostat being replaced rather recently, Im not sure what else to check. Any guidance would be greatly appreciated.

 

[Ou2mame]

Was the thermostat aftermarket do you know? I would start there.

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[robert2008]

The fact that it didn't overheat while driving on surface streets but did on the interstate at a fairly high rate of speed would normally point to a partially clogged radiator.

 

[old_man]

First off, Put in a new thermostat, Get a few gallons of water and head home, keeping it down to 55-60. See if it overheats again. As long as it isn't boiling over or running out of coolant, You should be able to limp home.

Check the serpentine belt and make sure it is tight.

 

[puntforloss]

If it is overheating at high speeds, it may be the water pump. The impeller will erode over time and it is probably cavitating at higher engine speeds. Pumps are cheap and you might as well pump, flush, fluid, new belt, plugs, fluids...

 

[old_man]

Don't forget the radiator cap. They need to be changed every two years. Even though they look good, they get where they won't hold pressure and you end up slowly loosing coolant.

 

[robert2008]

Any update OP?