Replacing An Outboard's Water Pump

Story 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.

Photo of dropping the gearcase to access the water pump

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.

1 | 2 | 3 | Next


 Recommended Articles
Gray rule

Thumbnail photo of outdrive corrosionHow To Prevent Outdrive Corrosion

The obvious and not-so-obvious mistakes that can cause severe corrosion damage, and how to avoid them

Thumbnail photo of a temperature gaugeWhat If Your Temperature Gauge Spikes?

When your engine's got a fever, quick action will often save the patient. Here's what to do when things start to heat up

Thumbnail photo of outboard flushingOutboard Flushing, The Right Way

It sounds simple, but hang on! There's a right and a wrong way to perform this essential task


Trailering Magazine is a benefit of BoatUS TRAILER ASSIST®.

BoatUS TRAILER ASSIST® provides:

  • On-the-road assistance for your trailer and vehicle
  • Special edition Trailering magazines
  • $15 coupon (off $100 purchase) for shopping at West Marine
  • Only $38 Annually! ($24 Membership + $14 TRAILER ASSIST)