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Old 19-04-2010, 05:57   #1
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Location: Simcoe, Ontario, Canada
Boat: Islander Mark II 30, 30ft - Zephyr
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Thermostat

Hello,

I finally got my motor running yesterday after working on it for a couple weeks. I don't think it has a thermostat installed it it. I did not open the thermostat housing to check but there always is water coming out of the exhaust outlet and the temp gauge never seems to rise, It is sitting at 100. It is possible that the temp gauge does not work and I would like to confirm that, but my question is what is the purpose of the thermostat. With an endless supply of water for the cooling system, why would there need to be a thermostat? Does the motor perform better at a certain temp range?

I am sorry if this is a basic question, I am just trying to decide if I even need to go to the expense to put the thermostat back in or not.

My motor is a Palmer p60. Raw water cooled
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Old 19-04-2010, 06:51   #2
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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 Engine Board:
Old Marine Engine: Palmer Engine Co

See also Basic Engine Gauge Theory & Testing
http://www.cruisersforum.com/forums/f14/basic-engine-gauge-theory-and-testing-645.html

HTH & good luck.
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Old 19-04-2010, 08:25   #3
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BTW: Palmer Marine Engine Manuals are for sale, here
Palmer Marine Engine Manuals - Palmer Brothers Service & Parts Manuals
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