I keep blowing the cap off of my coolant overflow tank and loosing antifreeze. I hot glues the cap down and it still blew off. It is on an 02 legacy 2.5. Any ideas on what may be going on. I changed the head gaskets last year but didn't machine or replace the heads. Could a head gasket going out again cause the high pressure? I would think that a leak would cause a loss on pressure. Could it be the thermostat stuck open possibly?

Thanks in advance for any input.

Gluing down caps ona prssurized system is the worst thing you can do. Be thankful it is just plastic that you tired to seal.

 

The cooling system is physically working as it should to deal with a pressure build up.

 

Odds are yes you have a HG issue.

Try a new radiator cap first.

try surfacing the heads i see thiss over and over and over the heads must be surfaced or the meatal gasket will never seal for long do a cly preshure test to see what cly is pushing into the cooling system. I have had to redo at least 8 head jobs thiss year same problem. If you dont surface the heads the coolant follows the path that previus coolant took past the headgasket like a crbon track on a spark plug. If it has a path it will always follow that path

Finally some good news. 7 dollars for a new radiator cap and problem solved. I'm sure ill have to do the gaskets again sometime and I think I will just buy new heads. But with 210k maybe I should just buy a rebuilt engine and be done with it.