Most inboard boat engines are cooled by raw water from the river, lake or sea. It comes in through a through-hull fitting, passes through a strainer that catches weed and rubbish, and is pumped by a raw water pump through the heat exchangers, where it cools the engine's coolant, then out with the exhaust. Like a car, the engine itself is cooled by coolant in a closed circuit.
In this video I explain how a Jabsco pump, and indeed any flexible impeller pump, works, and show some of the problems with priming the raw water side of the cooling system.
An outboard's water pump has the same kind of flexible impeller, down in the lower unit.
The sea strainer sits between the through-hull and raw water pump, catching weed and shells before they reach the impeller. I make a mounting board and angle brackets for it, then run hose to the pump.
An inboard engine's raw water pump is usually a flexible impeller pump driven by the engine. I strip a Jabsco pump and rebuild it with a new impeller, oil lip seal and mechanical water seal.
Like a car's radiator but cooled by raw water, a heat exchanger blocks with salt, weed and shells and corrodes. I clear the core with a weak acid soak and rebuild the housing with epoxy putty.
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