In an “open” raw water cooling
system, seawater is circulated through the engine
, and that sea water cools the engine
directly, then exits out the exhaust
. A thermostatic control valve may provide a bypass circuit to allow the engine to warm up to operating temperature. Water will always be discharged out the exhaust, whether cooling or bypassing the engine.
I’m not familiar with Palmer Marine
Engines, so take this advice with more than a grain of salt
Your engine was probably equipped with a cooling system that controlled temperature by utilizing a thermostatic control valve (thermostat) mounted in the head
of the engine. This control valve regulates the temperature of coolant
in the head
by controlling the amount of coolant
passing through the head. During a cold start of the engine, essentially no coolant flow occurres through the head. Instead, a bypass arrangement (from the tee fitting on the engine to the thermostat housing) allows all to the coolant to go around the block (bypass), until such time as the coolant in the head becomes hot enough to open the thermostat. This thermostat would theoretically maintain the temperature in the 140o - 180o F range, by opening further and further and eventually shutting off the bypass flow altogether if necessary.
The system presents several issues with regard to proper engine operation and temperature control.
1. The design concept
of "no flow until the thermostat opens" does not promote uniform temperatures within the engine and tends to cause the engine to go through significant "thermal trauma" each time it is started.
2. The bypass mechanism is prone to deterioration in performance due to wasting away of the "control boss" machined surface within the thermostat housing. This deterioration quite often leads to overheating
as too much coolant is allowed to bypass the block.
3. The original thermostat is designed to maintain 140̊ F which is much too cold for optimum operation with fresh water cooling.
You might check out the Palmer Engine Co
threads at the Old Marine
➥ Old Marine Engine: Palmer Engine Co
See also Basic Engine Gauge Theory & Testing
HTH & good luck.