How to Change the Yamaha 150 Outboard Impeller

by Don Bowman

It is good preventative maintenance to change the water pump prior to each boating season. Impellers, made of a flexible material, tend to wear rapidly and crack over time. All in all, it is good cheap insurance against getting caught with an overheating engine far from the dock. It is a simple and inexpensive procedure. It is best to replace the entire water pump for the small price difference.

Place the Morse control in neutral. Loosen, but do not remove, the nut on the leading edge of the lower unit just under the cavitation plate. Use a socket for this and the rest of the nuts to be removed. This nut will hold the lower unit up after all the nuts have been removed.

Remove the nuts on both sides of the lower unit. Remove the trim tab using an Allen wrench and remove the nut above it. Lift up slightly on the lower unit and remove the last nut. Lower the unit carefully. Pull the speedo tube off the lower unit.

Remove the two bolts securing the water pump to the lower unit. Lift off all the parts: the cup, O-ring, spacer, gasket and impeller. Install the new water pump in the reverse order with the impeller, the gasket, spacer and the water pump housing (cup) with a new O-ring on the bottom. Tighten the two bolts.

Place some grease on the splines on the gear shift rod and the drive shaft. Lift the lower unit and align the drive shaft. Lift the unit farther engage the gearshift rod. Align it with its hole and continue to lift it. Attach the speedo hose by pushing it on and lift the rest of the way. Align the plastic water tube with its fitting in the upper unit. Install the last nut removed in the front leading edge by the cavitation plate.

Lift the unit up as far as possible and loosely tighten the first nut. Install the rest of the nuts, including the one above the trim tab, and tighten all of them. Install the trim tab and tighten the bolt with an Allen wrench.

Items you will need

About the Author

Don Bowman has been writing for various websites and several online magazines since 2008. He has owned an auto service facility since 1982 and has over 45 years of technical experience as a master ASE tech. Bowman has a business degree from Pennsylvania State University and was an officer in the U.S. Army (aircraft maintenance officer, pilot, six Air Medal awards, two tours Vietnam).