1967 427 with Bassett headers Over heating Hallcraft drive

[87 concord]

Hi I have a 1967 flat bottom with a 427 BBC Hallcraft drive Bassett headers 143 degree t stat new impeller New hoses. It is around 160 degrees when idling but soon as you increase the rpm's it goes above 200 degrees . I am a Marine tech on Ski boats and I am not familiar With this kind of t stat housing moved away from the manifold with a plastic by pass that is pressure controlled. its a round insert with fins in the t stat housing. The t stat spring is facing the bow of the boat so it can sense water temperature from the engine. and release it down to the water ports on the headers. checked the intake hose up to the sea water pump checked pump housing. Tried different temp t stats, The sea water pump is picking up water at the lake takes a while to fill the block. No strainer so no possible bad seal. Can someone explain how that t stat housing works is their a certain direction that the plastic by pass needs to go? Ski boats do pump more pressure than I see coming out of the headers. I Thank You for reading this and possibly helping Joe

[87 concord]

Picture of t stat housing The Boat is made by Crown Marine and its a Wriedt Thank You

[Brad Zastrow]

A lot of performance engines do not use t stats. Take it out and see if it helps. I have used oil thermostats to keep the oil around 200 degrees to cook off condensation. Many engine builders have told me run cool but get oil temp.