Over heating Problem

I have an 89xj that runs fine on the freeway or open roads well under 200 but as soon as I start to climb altitude or playing around the things jumps to well over 210 and all the water boils out of the fill bottle. I have replaced the thermostat and now I am thinking about replacing the radiator with a new 2 core modine and having the fill bottle by passed. I now there are quit a few items that make up the cooling system, I was just currious to see if I am on the right track. Any help would be appreciated.

If the radiator cap is more than a year old, replace it with a standard 16 lb unit. This is THE most common reason for boil over under load. It is a quick cheap thing to do and something you should do every couple of years anyway.

Tim are you talking about the cap on the fill bottle? I do not have a radiator cap with the cooling system i have right now.

Replace the fill bottle cap, and make sure you don't have a crack in the bottle. That can also cause you to overheat.

I had a similar problem two years ago with my '89. I went through 2 new bottles and three new caps - it appeared that there was a manufacturing defect in each case, and the dealership refunded my money. I went to the open system and my xj has never had a problem with overheating.

I've got an '88, I had the same problems last summer. I was going to switch to the open system but the radiator shop said I could'n't due it because of a sensor I've got on my current radiator. So I just replaced my overflow bottle with a alluminum one with a radiator cap.

Also, my Jeep would run fine while I was moving but when I stopped or put it under stress it would overheat. This was due to it running lean, so replacing the O2 sensor solved that.

~Scott