It's a poor design, to start with IMO. I also have an '89
, but I think this issue is one most of has been victim to one way or another. Mine leaks from the cap on the "pressure tank". When I bought it from my buddy, he mentioned that he had replaced the tank several times, from it splitting wide open. You might want to have a look at www.madxj.com
, look under "technical" then click "engine" and "budget cooling upgrade (Closed to Open)". I'm seriously thinking about performing this on mine.
Have you burped the cooling system? Ie. gotten all the air out of it, because the air will expand alot farther than the coolant at raised temps. thus forcing coolant out where ever it can find a path.