Driving home today in 108º weather here in sunny Las Vegas, Nevada and remembered I needed a few things from the Walmart. Stopped at one near my house, turned the Jeep off. I wasn't inside for more than about 10 minutes and when I get back in my Jeep and turn it on, the first thing I notice is the temp at damn near 260º. After running for about 5 seconds the temp stabilized at about 210º where it's supposed to be.

Is it normal for it to do this? I've noticed it before even in colder weather.

You need a new thermostat. They are cheap and easy to change out. It's not normal, and the fact it happens in all temps is a strong indicator. We had 102 here in North Georgia today and my 2000 Sport was at 210 all day.

I just recently had my thermostat changed, about 2 months ago. And my radiator re-cored at the same time.

Buy a "Fail-Safe" thermostat and flush the entire liquid cooling system. That will help if not solve the engine cooling problem.

Be responsible with the coolant waste. Dogs and Cats will lick up coolant and afterward die. Don't kill your neighbor's pets!

It's the thermostat. Over heating full of fluid in the winter is not normal.

Read the post again. Drove to Walmart. Shut it off. Went into Walmart. Came out started vehicle temp was above normal (260), Stabilized (cooled down) after running. Coolant temp. rises when there is no flow (not running). Perfectly normal for the temp to be higher when you first start vehicle especially when it is 108 degrees outside and it had only been 10 min. since you shut it off. As long as your temp dropped after you started it you are ok. As stated not a bad idea to get a fail safe thermostat but I wouldn't do it until you are having issues of it "running" hot. Might also want to do do a 70/30 mix on your coolant to raise your boiling point of your coolant. I know what you are going through. Lived in Bullhead as a kid.

Your system is working fine. Once the engine is turned off the coolant stops flowing and traveling trough the radiator. As the coolant sits in the engine it absorbs heat. When you restart the engine and the coolant begins to circulate again it carries that absorb heat and travels past the temperature sensor and that indicates the 260 you see. After it circulates through the system and back trough the radiator a few times the heat is disapated and the temperature on the gauge drops back down.

Not Dissing your answer Fweaky, but my 90 YJ 2.5 hasn't ever acted that way at high temps.

That may happen on the six cylinders, but maybe not on the 4 cylinders?

When an engine is shut down core temperatures sky rocket. Coolant temperature increase AFTER engine shutdown is a normal condition.

Operating temperature of 210 degrees F is a normal condition as well. The fact that you restart and engine temperature returns to normal operating temps tells me your cooling system is working.

I wouldn't recommend running out and replacing parts. Check your cooling system over when its cool, and then hot.

First...make certain your coolant level in the radiator is at the fill neck. If it's low you will need to add coolant and possibly bleed the system of trapped air...this is another process for another post.

Consider replacing coolant if its older than 3 years.

Check your radiator cap. Have your shop pressure test it.

Check your hoses and clamps. Replace old, cracked or swelling hoses.

Check your fan clutch. With the engine off, spin the cooling fan manually by hand. It should spin but with some resistance. If the fan spins feely you need to replace the fan clutch.

Check for debri and BUGS on the front side of the radiator.

I think this is enough to get you started and give you some peace of mind. It's HOT out so expect higher temps.

Thanks for all the help everyone. I had just recently replaced the thermostat because while I was replacing my timing chain, the bolts on the thermostat housing broke off inside the head. Had to have a shop extract them as I had no previous skill in doing this. They extracted the bolts and installed a new t-stat for me. I had my radiator re-cored at the same time all of this was happening because I had to take it out anyway to do the timing chain.

I haven't replaced the hoses but I will do that today. I will try the 70/30 mix and I'll throw in some fresh oil just for the heck of it.

Thanks again!

I run a mechanical and an electric gauge on my V8 and the mechanical gauge reads with the ignition off. You can watch the temperature climb when the engine stops. You don't see it on the electric gauge because when you start it up it drops down fast. It depends on the placement of your temperature sensor I guess. A coolant mixture of 50/50 is more efficient at transfering heat than 30/70. Straight water is more efficient at removing heat than antifreeze. Antifreeze contains corrosion inhibitors that keep the system clear of scale and corrosion and thats why manufacturers suggest that ratio. The only thing 70/30 mixture will prevent is freeze up if you drive to the north pole.