I tapped off of my heater core lines to run coolant to my gt3076r which would be the only thing I changed on my coolant system for my build. I fill up my reservoir and a few miles down the road, my pressure cap opens up and drains 90% of the coolant out of the reservoir...running down the engine bay. what is causing this pressure? and how does it purge that much of the coolant reservoir?

 

coolant is too heated and building pressure?

 

ahh. its prob a head gasket