my rex is building pressure in the coolin system and blowin out the over flow tank but she aint overheatin what could my problem be ?

 

Excess pressure in the cooling usually indicates compression leaking into the cooling. A sure sign would be coolant coming out of the exhaust....

 

Try the various solutions in the FAQ (look for "cooling", "overheating", etc.).

Try running the car with the radiator cap off. If coolant gushes out, you may have a blown coolant seal. That'd require an engine rebuild.

If you have too much coolant in the system, it'll also do what you're describing. Top off the system through the radiator cap, then empty the overflow tank to allow room for the excess. Drive your car for a bit. If it still gushes out the overflow, you got another problem. If the overflow fills a little then stabilizes, then you're in good shape. From there just fill it up to the "FULL" line, no higher, and you're done.

I'd also replace the radiator cap, on the chance that it might be stuck. It's only $7. The purpose of the radiator cap is to release excess pressure.