Guy brought a truck over today said he was leaking coolant out the overflow . The truck sat for a couple hours and cooled off. started the truck and after a minute of idling the upper hose is very hard and I can see a steady stream of bubbles coming into the coolant tank and it starts puking coolant. I let it run like that for a few minutes then took the cap off and a massive amount of pressure and a lot of coolant came out, enough to get on the top of the cab. Keep in mind the motor was cold. Could an injector cup leak that much compression by or does it sound more like a hg?