470 Overheat

[dan4836]

I tried just about everything...

My boat runs great except a very slow heat up after 3200 RPMs until boil over.

I replaced:

1) Thermostat
2) Water pump and housing (twice to be sure)
3) Removed the 3" heat exchanger and replaced with 4"
4) Flushed out the seawater circuit
5) Removed the riser and flushed and cleaned

I installed a new 160 degree thermostat. For some reason, my temp will stay at 120 at rest and increase past 200 very slowly at 3200 rpms

Can the thermostat be installed up side down? I have the springs facing down. One forum I read states the sealoc manual shows this install incorrect.

My only other option is head gasket?

Any thoughts?