How to Change the Impeller in an Evinrude Motorby Chris Stevenson
The Evinrude marine outboard motor uses a water pump in the lower unit case to circulate water through the engine passages and manifold. The water pump keeps the motor within normal operating temperatures. The procedure for replacing the rubber impeller inside the water pump is basically the same for long- and short-shaft motors. You should have a boat owner's repair manual nearby, since some models differ in configuration and design. Impeller kits can be obtained from any marine supply store, complete with gaskets and new mounting hardware.
Stabilize your boat with wheel chocks if it remains on the trailer. Disconnect the negative battery cable on your marine battery with a socket and remove the ignition key. Locate the mounting bolts that hold the lower unit case to the upper unit. Small engines might have only two bolts, while larger engines may have four or five. Loosen and remove the bolts with the proper size socket. Have an assistant help you lower the case just an inch or so.
Locate the shifting rod that extends down into the lower case. Remove the small coupler bolt that holds the two shifting rods together and pull the coupler out. Pull the lower unit down and free of the upper case. Take the lower unit to a work bench and lay it on its side, letting any gear oil drain into a small pan. Use a socket to remove the two or three bolts on the top of the impeller casing and pull the casing up over the drive shaft. Flip the impeller casing over.
Note whether the rubber impeller blades inside the case spin left or right. Pull the impeller out, making sure not to lose the shaft key, if it has one. Clean out the inside bore of the impeller housing with carburetor cleaner and a rag. Lubricate the inside of it with petroleum jelly. Place the new impeller inside the top casing in the correct blade orientation, and insert the shaft key, if so equipped. Slide the casing down over the drive shaft and align it with the mounting holes.
Clean the upper and lowering impeller case mating surfaces with a gasket scraper. Install the new gasket on the upper casing. Slip the upper casing down over the drive shaft and align it with the mounting holes. Screw the mounting bolts into the top case and tighten them with a socket. Have your assistant help you transport the lower unit back to the boat.
Place the lower unit upright and propped by wood blocks so that the lower unit aligns with the upper case. While your assistant raises the engine, align the drive shaft to fit up into its spline sprocket. At the same time, guide the inlet water tube so that it will seat in its seal. Prop the engine up higher until a one-inch or greater gap remains between the upper and lower unit cases. Carefully align the shift rods and connect the coupler to them. Insert the coupler bolt and tighten it with a socket.
Have your assistant push the lower unit case up higher, while you check the water inlet tube alignment. When the cases meet flush, screw the mounting bolts in quickly by hand and tighten them with the proper size socket. Loosen the lower unit gear oil cap and replace any gear oil that you lost during tear-down. Do not test the engine until the lower unit and propeller are submerged.
- If you have trouble aligning the drive shaft with its spline seat, rotate the propeller blade until the shaft slips in.
- There might be an inspection plate in the side of the upper case that you must remove to disconnect the shift linkage. Check your owner's manual for the correct removal procedure.