The impeller on a 150 XRI Mercury outboard is made of polyurethane. It is the heart of the water pump. The impeller sits on a metal plate and covered with a metal cup. The driveshaft runs through the center and is the driving force for the pump. The impeller is subjected to wear from particulates in the water and from rubbing. A water pump kit is quite inexpensive and should be replaced prior to every boating season, from a safety standpoint.
Place the morse in neutral. Remove the engine cover and the bolt securing the gear shift linkage. Tip the engine up 20 degrees so it is not straight up and down. Loosen the nut with a wrench on the front top leading edge of the lower unit close to the cavitation plate. Do not remove this nut because this will be used to hold the lower unit on until all the nuts have been removed.
Remove the nuts on both sides of the lower unit securing the lower unit to the upper unit, using the appropriate socket. Remove the bolt in the trim tab, using an Allen wrench. Remove the nut located above the trim tab, using a socket.
Lift up slightly on the lower unit and remove the remaining nut in front of the cavitation plate. Lower the unit to the ground. Remove the hose from the top of the water pump. Remove the four bolts in the water pump housing using a socket. Lift the water pump housing up and over the driveshaft followed by the impeller, the gaskets and the lower plate.
Install the new water pump in reverse order of removal. Place the plate over the driveshaft and down into place followed by the gasket. Install the key in the driveshaft slot for the impeller. Install the impeller followed by the housing. Install the four bolts and tighten with a socket. Install the hose.
Raise the lower unit and align the driveshaft and gearshift with their holes as it is lifted. Plug the water pump hose on the fitting in the upper unit. Install the first nut, which was the last one removed. It only needs to be hand tight at this point.
Install all the nuts on both sides of the lower unit and the one above the trim tab. Tighten all the nuts securely with a socket. Install the trim tab and tighten with the Allen wrench. Install the bolt in the gear shift linkage in the lower front of the engine.
