Impellers, thermostats and water pumps are essential components to regulating an efficient working temperature in your marine engine. Engines passing seawater through the system will inevitably require service. Simple routine maintenance of cooling systems will assure your vessel is ready for its next adventure. Flush raw water systems on the trailer or at the end of the season. Failure of these components will overheat an engine, possibly leading to costly damage of core components.
Water pumps with rubber impellers burn out if run dry. This could be caused by simply forgetting to open a seacock. Another common cause at sea is weeds or a plastic bag stuck in the seawater intake through-hull. Having spares on hand is highly recommended. As impellers age they lose there flexibility and should be replaced.
The thermostat is a simple valve which opens once the engine has warmed, thus allowing the coolant to circulate. On most engines the thermostat will pop at 160 degrees F and be fully open at 180 degrees F. To troubleshoot, remove a suspect thermostat and place it in a pot of boiling water with a thermometer. A malfunctioning thermostat must be replaced.