Koy Radiator and High Pressure Radiator Cap
 

I just installed a new Koyo 53mm radiator into my 1988 rx7 10th AE. Everything fit well and installed well well except for 1 problem....

I installed the 1.3 radiator high pressure cap that came with it and I'm guessing it added too much pressure to the system on the upper hose and coolant came flooding out the stock coolant filler cap.

My question is if I replace the coolant filler cap with another 1.3 radiator high pressure cap will it overflow again or just keep the system pressurized and be fine?

Try a 1.1 bar cap , stock is .9 so 1.3 is fairly high pressure , and your other cap could be bad or installed incorrectly