1984 9.9 cooling issue

[tnpuddleduck]

My motor will pump well for about 15 minutes, then stop. I blew air completely
through system and its clear. Put it back in water, it pumps great for 10 minutes, then quits. Can someone give me an idea what may be going on.
(Complete new pump kit installed)


Thanks

[boats.net]

Check compression to see if has a blown head gasket, might need to to check grommets on water tube going into engine.