1967 427 with Bassett headers Over heating Hallcraft drive

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

Picture of t stat housing The Boat is made by Crown Marine and its a Wriedt Attachment 523840 Thank You

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.

The thermostat housing on your 1967 flat bottom with a 427 BBC and Hallcraft drive appears to be a pressure-controlled, round insert type with fins, positioned away from the manifold. This design is often used to regulate water temperature and maintain proper engine operation. Typically, the housing is designed for water to flow through it in a specific direction, with the spring side facing the engine and the water inlet side towards the radiator, ensuring proper circulation. Regarding the plastic bypass, it usually acts as a pressure-controlled valve that allows or restricts flow to maintain optimal pressures within the system. Its orientation generally needs to align with the flow direction for correct operation, but specific instructions from the manufacturer or a visual inspection for directional markings should guide the proper placement. The fins in the housing help improve water flow and heat transfer, preventing hot spots and aiding in temperature regulation. In your case, since the housing has fins and a pressure-controlled bypass, it’s best to ensure the bypass is installed in the correct orientation as per the manufacturer's guide—usually with the spring facing the engine to allow hot water to circulate through the cooling system effectively. If the bypass is directional, it’s critical to follow the original setup to avoid disrupting the flow and cooling efficiency.


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