I assume you are running a 50/50 mix of distilled water and
antifreeze with some water wetter in it. Also, you need to move up to a higher pressure cap as 13 is too low. I run a 16 and many are running higher then that. Make sure you have some good engine compartment seal ie the air is going into the radiator vs over and into the engine compartment. Last would be some bigger fans but I think the cap would stop it from spitting out.