Jeep has been running good. Temp sensor was not working when I got it a month ago. I put a y block on there and ran an aftermarket temp gauge. Today 20 min drive home from junk yard gauge was reading 230-250 pinned! Rad cap was smoking. My buddy said get different cap. Any thoughts on cause or a possible fix. Also could these high temps have caused damage?

 

It's a 96 auto that was reading 160-180 even wheeling prior to today ....

 

Many parts to the cooling system.

Water pump, radiator, radiator cap, thermostat, fan clutch, hoses, serpentine belt that runs water pump.

What is the history of routine cooling system service and how many miles on the above components?

 

I got jeep a month ago with 159k on the dash. Signs of a Possible motor replacement. I've only put a few 100 on it. So no real telling. Thing was it has been fine before this afternoon ...

 

That's the way most 15 year old vehicles are, without proper maintenance......fine one minute, broke the next. XJs luv to have their hood raised at least once a week.

 

As mentioned could be a number of things. I'd eliminate the couple of most obvious and easiest/cheapest to fix first. Water pump and thermostat. Other than that make sure the fan is coming on as needed.

 

Before you replace anything, check your fluid levels, then burp the system of air (Im guessing its your 96, which means its a HO engine.)
Just run her w/o the radiator cap for a couple of minutes, making damn sure you dont let the fluid level drop from the cap.

 

Could be a plugged radiator, or even a cracked head.

 

I vote sticky thermostat

 

Ok so I replaced the the Tstat last night, only had a 180. Put the oem 195 on. It seems the cap was prob the cause as it was not venting properly and most of fluid turned to steam and seaped out. Going to get a new cap today and see if the fan ever come comes on .... Thanks I will let y'all know what happens.

 

Does your heater blow hot air? If not then coolant is not circulating. Thats how I found out I needed a new water pump.