Whether you change the impeller in your 1997 Mariner outboard because of damage, diminished performance or just as a part of maintenance, you lengthen your motor's service life. Should the impeller fail, catastrophic motor failure follows quickly. Just as the water pump housing is the central collection point for your outboard's cooling system, the impeller is its heart. As water is drawn into the motor through the water inlets, the impeller drives that water throughout the motor's cooling galleries and the smaller, more remote reaches of the motor, to capture its excess heat and deliver it to the sea.
Set the lower unit into a bench vice to allow you free access to the water pump, located on top of the lower unit. Lift the driveshaft seal from the top of the housing of the water pump and slide over the top of the driveshaft.
Remove the four mounting bolts, located at the corners of the pump housing, using a 1/4-inch socket wrench or a 1/4-inch open-end wrench. With the mounting bolts removed, lift the pump housing and the gasket that seals its lower edge up the driveshaft; slide them off.
Rake a fingernail across the housing; if it catches on the impeller sealing groove, that's acceptable. If the nail catches on any other groove, discard and replace the housing,. Absent this damage, set the housing aside and discard both its gasket and the gasket from the pump's face plate.
Grip the old impeller. Lift it up and free of the driveshaft. Locate the Woodruff key, that links the impeller and the driveshaft. Pull the key free of its notch in the driveshaft and pocket it for use with the new impeller. Note that in this model, there is no impeller insert.
Run your fingernail over the face plate, still on the lower unit, as you did with the pump housing. Grooves cut in the face plate dictate its replacement as well as that of the pump housing.
Locate the two "locating pins" in the water pump replacement kit and fit them into the mounting bolt bores on the lower unit. These will assist you in obtaining the proper orientation for the gaskets and in holding the gaskets in place as the pump housing is installed. Align the hole patterns of face plate and "small hole" gasket and slide them down the driveshaft, if the face plate and gasket require replacement.
Apply a thin coating of gasket sealant to the gasket mating surface of the water pump housing and on both sides of the "large hole" gasket that serves the housing. Set the new "large hole" gasket onto the top of the face plate. Take the Woodruff key from your pocket, touch the Woodruff key into a jar of petroleum jelly and set it into its place on the driveshaft.
Push the impeller down the driveshaft so that the impeller's key-way aligns with the Woodruff key and press the impeller into its place on top of the lower unit. Lubricate the inner surface of the pump housing with waterproof marine grease. As previously noted, this model does not have an impeller insert.
Place the pump housing over the end of the driveshaft and slide it down over the locating pins and onto the impeller. Press the cover downward, gently, while rotating the driveshaft to the right, clockwise, until the pump cover seats itself properly on the face plate.
Thread the water pump mounting screws into place and then tighten them in a crisscross pattern to 60 inch-pounds with a torque wrench. Slide the driveshaft seal down the driveshaft and press it into the pump housing until its flared section is slightly more than 1/3 inch -- somewhere between 0.32 and 0.38 inches -- above the top surface of the pump housing.
Items you will need
- Water pump replacement kit
- Bench vise
- 1/4-inch socket wrench
- 1/4-inch open-end wrench
- Gasket sealant
- Petroleum jelly
- Torque wrench
- "Mercury/Yamaha & Mariner 2.5 - 225 HP, 1995-2004"; Seloc Marine; 2007
- Old fashioned water pump image by JKeen from Fotolia.com