ok here's the skinny...here is what is happening in a nutshell.. cherokee runs good, except with a slight skip at idle but no other symptoms . but then suddenly out of the blue while traveling the temp gauge pegs out and then sprays coolant outta the radiator cap, also see coolant in the overflow reservoir. I let it cool down add fluids and back to normal until the next time..it has happened 3 times now with several days/weeks between happenings and after each time i have pulled thermostat and replaced. still happening. The napa brand was the last thermostat used and prior was the autozone brand so its not the thermostat brand fault .I feel like something maybe obstructing the thermostat. I have( replaced radiator 3 years ago) recently new water pump ( autozone) new thermostat (napa brand heavy duty)..new radiator cap any suggestions as to what maybe causing this issue?....head gasket?
no oil in coolant, no coolant in oil, no smoke what so ever.. runs like a champ other than the skip at idle ...

 

you have any hoses that could be pinched? or a possiable blockage in the radiator?

 

no hoses pinched.. i have flushed the radiator each time i have changed the thermostat and water pump.. my next move is to remove thermostat, put back together with out and do a coolant system flush.. to see if anything may come out.. just boggles me as to how it runs and cools fine then boom...overheats out of the blue... crazy stuff!

 

ya these Cherokees aer unpredictable aat times I don't think its a head gasket probm. if you don't have mocha oil your free of that sin lol

 

X2 on flushing the system. Flush the radiator, heater core, and block all separately to check for blockage. You could just have had an air bubble in your system too.

 

Sounds like the cap is defective, it should not spray out any coolant. Is the coolant level at the full - hot mark?

 

Run w/o a thermostat for a while and see if it does it that way. This could also help loosen up anything that could be causing the problem.
If you really need it to keep temp you can use a washer(56mm or 58) that has a 3/4 or 1 inch hole in it as a restrictor but allows coolant to flow freely, till you find out what's wrong.

 

Pull radiator check for debri in side tanks that will float up and plug passage ways. Suspect side is drivers tank...

 

Thanks for the responses , I'm gonna flush, and tune up to see if it fixes my issue.. I'll keep ya 'll posted

 

And change the cap....cheapest and easiest item that is almost always overlooked...