I have a 90 Jeep Cherokee 4wd 6cyl 4.0L and am having a radiator problem. The radiator has been replaced twice in the past year(2008) and its starting to leak again. It was last replaced in Nov 08 and the new radiator has approximately 2000 miles on it. All of the leaks are on the passenger side near the bottom in the seam. I was having a problem with the over flow bottles on the sealed system expanding and caps failing and now the radiators are blowing out. Anyone have any ideas why the system would be over pressurizing or what would cause the failures?

Did you replace the radiator with one from the same source each time? If so, I'd first go back to the source of the radiator, especially if they gave you a warranty.

If you have a good radiator cap, that will release pressure LONG before the radiator gets a leak....radiator caps are PSI rated, with 18PSI being about right (it's what is on my 04 GC).

If you're replacing with a used OEM radiator, then that's the problem...they get leaks at the seams, and all seem to start leaking after awhile. There are a lot of aftermarket radiators out there. I did a search at the Cherokee forum, have a look and find one that will work for you:

http://www.automotiveforums.com/vbulletin/search.php?searchid=2460584