The one problem with plastic tanks is that they expand and contract at a different rate than the aluminum. This can lead to stress points where the tanks mate to the aluminum core.

 

Ok now I feel real stupid. I did a pressure test on the radiator with a rented tester, and it holds pressure just fine. I then tested the cap and it didn't hold more than about 8 lbs. Amazingly enough, a new cap tested and held all the way up to 16 lbs. The real test will be today in the 90 degree heat towing the boat uphill. I expect it'll pass!

 

a nascar(3 row) radiator from autozone works for me--wish i had one in my 89--they cost more for a dodge than a ferd or chevy-imagine that!!!!!