I noticed last summer my 97 TJ would run close to the red on hot days with the AC on, this summer its a bit worse, she will overheat on a hot day with the AC, and very high with out AC. I tested the thermostat in a pot of water with a thermometer, I replaced it for cause but the old one was fine. Fan clutch is good too, Is it time for a new radiator?

Doug

The temp sender and gauge may be part of your problem. I would never replace a working radiator in a Jeep until the one I have makes the coolant PUKE out the overflow.
Your Jeep actually runs better at 230/240* than it does at 195*.
Big Jim <img src="/forums/images/graemlins/pfft.gif" alt="" />

Thanks for the reply Jim,

I opened the radiator cap and placed a meat thermometer in the water the meat thermometer matched the dash gauge, and in a short amount of time with the engine idling I was boiling water. I was hoping it was a bad thermostat, but as previously mentioned, it tested good and was just replaced with new.

So if the engine is good, thermostat and fan are also good.....only thing left is a neglected 10 year old radiator, did I miss anything?

You may have a partially-cloged radiator, but keep in mind...

Water in a non-confined space (radiator with cap off) boils at 212 deg F. The purpsoe of the pressure cap is to increase the temperature at which water boils. It raises the boiling temperature about 2-3 degrees for each lb of pressure. So, a radiator with a working 15-lb presure cap won't boil until the water temp hits 240 degrees or more.

How does your coolant loook? Is it nice and clear green (or whatever the colorof your antifreeze)? Oris it brown and rusty looking>

Also, remember that you can sometimes get rid of a lot of gunk in the cooling system by draining out a pint or so, pouring in a can of cooling system cleaner, and then subsequently back-flusing and cleaning the radiator, and filling with new coolant mixture. I'd try that before spending the money on a new radiator.

Bob is right on the money when he wrote:
Water in a non-confined space (radiator with cap off) boils at 212 deg F. The purpose of the pressure cap is to increase the temperature at which water boils. It raises the boiling temperature about 2-3 degrees for each lb of pressure. So, a radiator with a working 15-lb presure cap won't boil until the water temp hits 240 degrees or more.

I couldn't agree more! If the coolant looks good I'd drive her till she pukes!
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

Thanks for the reply, I did drain the radiator, and did a flush on it, the coolant was in fair condition still had a greenish color to it. Every car I own will idle in the drive with a cap off...except this one...lol thats what makes me believe the radiator has enough blockage and dosent have the area to cool the engine anylonger

If you start it with the cap off TOMORROW after it has had time to cool to ambient temprature and it boils at that time...you have a bad head gasket! Just sitting with the engine cold if you get bubbles they are from compression leaking into the coolant jacket.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

I checked, no bubbles, looks like the head gasket is ok. Fan clutch is good, radiator is clean and bug free

The Jeep runs great until the ambient tempature reaches over 90, and with the AC on it over heats.

If you go back on this board 2 or 3 years you will find that there have been many complaints zackly like yours.. In EVERY complaint the jeep was NOT overheating.
I have thought for a long time that the gauge is more sensitive than the gauges on other vehicles.
It seems that a 10* rise in temprature pushes the needle farther toward the red line than other vehicles. Although the driver THINKS the engine is too hot it really isn't.
Our advice in all instances is to drive the jeep until it pukes it's coolant out.. It seems they NEVER do!
The gauge is only there to warn the driver of a potential coolant loss. As long as the coolant remains in the engine the engine CANNOT get too hot! ONLY without coolant can your engine be hurt by heat. Your engine really LIKES 20 or 30 degrees over the normal 200* operating temprature.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

I did notice what you just posted, the gauge makes that jump into the red more quickly that the engine could possibly heat, and jumps back fast too when you slow down & turn off the AC.

Where does the engine warning light get its information, gauge or additional sensor? I ask because when the gauge does the leap into the red, the engine light comes on too and I hear the warning chime too.