What is Raw Water Pump?
The raw water pump is a belt-driven or gear-driven pump mounted on the engine. It draws seawater through a through-hull fitting and seacock, then circulates it through the heat exchanger and out the exhaust.
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What it is
The raw water pump is a belt-driven or gear-driven pump mounted on the engine. It draws seawater through a through-hull fitting and seacock, then circulates it through the heat exchanger and out the exhaust. The pump contains an impeller that rotates inside the housing to move water. The complete system includes the bronze through-hull fitting below the waterline, the seacock valve that controls water access, a raw water strainer to prevent debris from entering the pump and the pump with its impeller.
What it does
As the impeller spins, it pulls water through the seacock and raw water strainer, then delivers it through the engine’s heat exchanger for cooling. The seacock allows you to shut off water flow when the engine is not running, which helps prevent flooding if a hose or fitting fails. Always check and open the seacock before starting the engine. When the system is functioning properly, a steady stream of cooling water will be visible exiting through the exhaust.
Why it matters
The raw water cooling system is essential for your engine’s survival. Loss of water flow can quickly cause overheating and severe engine damage. The impeller is the most vulnerable component and can be destroyed if run dry. Broken impeller blades may clog the heat exchanger and reduce water flow. A seacock that cannot close creates a serious flooding hazard if a hose fails. Problems with the raw water system are among the leading causes of marine engine failures. Regular maintenance, including replacing the impeller, inspecting hoses, cleaning strainers and monitoring exhaust flow during operation is inexpensive and can prevent catastrophic engine damage.
General Maintenance
Before starting the engine, open the seacock and make sure it moves freely. Check for a steady flow of cooling water from the exhaust immediately on startup. If the flow weakens or stops, shut the engine down immediately to prevent damage. Replace the impeller at least once a year, every 300 hours or as necessary. In sandy or debris-laden waters, replace impellers more frequently. Always carry spare impellers. Exercise the seacock monthly by opening and closing it several times to prevent it from seizing. Seacocks should be disassembled, cleaned and regreased or replaced every 2–3 years. Inspect through-hull fittings annually during haulout.
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