Replacing an Outboard or I/O Water Pump Impeller

New England Boating’s Tom Richardson with Phil Batista from Burr Brothers.

When was the last time you replaced the water pump impeller on your outboard or inboard/outboard engine?

If the answer is more than 2 years then you should probably tend to this necessary boating chore.

To learn what’s involved, check out the video and article below. While the video shows the steps for replacing the water pump impeller on an outboard, the steps are similar for an I/O engine equipped with a lower-unit water pump.


The accompanying video is not intended as an instructional demonstration. Rather, its goal is to illustrate how outboard engines function and the extensive training and skills needed to repair and service modern marine engines. No one should attempt to repair or service an outboard engine without training by a certified instructor. Doing so could result in personal injury, engine damage and violation of the engine’s warranty.

The water pump on an outboard or I/O is a critical part of the engine’s cooling system, allowing raw water to circulate through the powerhead to prevent overheating. A key component of the water pump assembly is the rubber impeller, which spins inside the lower unit to provide the suction and pressure needed to supply water to the powerhead. Over time, the rubber can deteriorate and lose its elasticity, which can lead to a loss of pressure. Internal gaskets, rings and seals can also break down, allowing water to escape inside the engine housing and, again, causing a loss of pressure.

It’s generally recommended that the impeller and related cooling system components be replaced every 100 hours, which for the average New England boater translates to 2 seasons of use. As you’ll see in the accompanying video, performed at Burr Brothers Boats in Marion, Massachusetts, this is not a project for the novice mechanic, as there are numerous steps involved, including removal of the lower unit. It’s also possible to damage the engine if the various parts are not installed correctly according to the manufacturer’s specifications.

At Burr Brothers, outboard technicians undergo numerous hours of training in engine service and repair, plus they have all the tools and equipment needed to get the job done right. Once you see all that’s involved, you’ll no doubt gain an understanding and appreciation for the work of marine technicians in general.

The engine shown in the video is a 2004 200-hp Mercury OptiMax. Note that different engine models and brands will require different steps for replacing the water pump.

To contact Burr Brothers:

  • Call: (508) 748-0541
  • To visit the Burr Brothers website, CLICK HERE.

Related videos:

Performing an Outboard Leakdown Test

How to Change Your Lower-Unit Oil

Note: Burr Brothers is an authorized dealer for American Honda, Mercury, Yamaha, Evinrude and Johnson. Its engine technicians are trained to the Master Technician level, with more than 55 years of experience among them. Safety is the number-one concern at Burr Brothers Boats. A lot of “safe practices” are invisible to the untrained eye, or not captured on video. The work shown in this video should not be attempted by untrained individuals.