Replacing An Outboard's Water PumpStory And Photos By John Tiger
Published: Fall 2013
Don't be put off by the fact that you have to drop the lower unit. Here are some tips to get you through it.
1. Dropping the gearcase to access the water pump requires removal of the mounting bolts.
Outboard water pumps are simple designs. Located just atop the lower gearcase assembly, they're easy to access and service, too. The pump houses a rubber impeller that's keyed to the engine driveshaft. Water enters the lower gearcase through inlets on the sides of the gearcase, just above the propeller shaft area. The driveshaft turns the pump inside a plastic housing with a stainless steel liner. The pump draws water through the intakes and up into the housing. The impeller blades (vanes) touch the liner at lower speeds as the driveshaft turns, but as the engine revs up, the impeller blades bend back away from the housing liner. The pump sends water out of the top of the housing through a brass tube, typically about a half-inch in diameter, up to the engine's powerhead, where it circulates through the system's cooling passages.
Salt, sand, mud, sticks, and other debris take their toll on the pump impeller, housing, and related parts. That's why most outboard technicians recommend replacement every season, or at worst every other season. There are legions of stories that go "I've had my outboard for twenty years and never replaced the water pump"; however, good preventative maintenance practice includes replacement of the pump and housing at regular intervals.
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