A friend told me that low engine operating temperature is a sign of a defective thermostat. Is he right?
Sometimes it is. Low engine coolant temperature which persists after the engine has been run under load for an appreciable length of time means either a missing thermostat, a defective gauge/sender, or (in cold water) a sticky or poorly sealing thermostat. You can check the actual water temperature by holding a portable surface thermometer against one of the middle cylinder head studs. It will read the real cylinder head water temperature, which is the temperature the gauge should read if the gauge and sender are properly calibrated and working correctly. The large single spring fitted to the new Atomic Four thermostat supplied by Westerbeke has less pressure than the 3 small springs used on the OEM Holley thermostat originally fitted on engines made after 1968. If there is any restriction in the bypass line and/or a higher pressure Oberdorfer M7 (full cam) water pump has been fitted, the pressure developed by the water pump will actually overcome the force of the spring and open the t
