Mercury 2001 Saltwater 125 Horse Impeller replacement

After 5 years of no problems and noticing that my  water pressures were falling I decided to change out the water pump impeller on my engine. I had been told that this was a real tough job to do because my engine was a saltwater style motor, boy somebody is lying cause this job was so simple start to finish took only one hour.

First you need to put the shift lever in the forward position which engages the gears for the prop, I then grabbed a hold of the prop and turned it till it stopped, it will click if you go the wrong way.

I then tilted the motor all the way up so it would be easy to handle.

I turned my battery selection switch to off which allowed no power to the motor don't want this bad boy to fire up while I have my hands on the prop.

There is a total of five nuts that hold the lower unit on two on each side of the unit and one that passes through a anode at the back of the unit they are all 15 mm in size, had to use an open end wrench for the ones under the plate and a socket for the other.

After removing the nuts I grabbed the entire unit and it slide right  off, total shock as I really thought it would be stuck after five years of use.

This is what you have after removal of the lower unit, I had a log come up and bust off the front of my cavitation plate, so that's why it looks the way it does.

There are 4 bolts that hold the impeller housing to the unit they are 10 mm, remove them and the unit lifts straight up off the shaft

I don't have it in the picture but I have removed the impeller and the bottom wear plate that sits on the shaft.

Old one on the right vs. the new one

This is the stainless steel housing just turned upside down, I took the new Impeller an put it inside the housing then lowered it down on the shaft and aligned it with the impeller key, very easy to do, just watch that the impeller key does not pop out, it basically sits in a flat that has been milled into the shaft and has an area that the impeller fits down onto to allow the shaft to drive the unit. I marked which way the impeller vanes were angled so that the new one would be the same. Tighten down the bolts to the pump housing and your ready to install it back on the motor.


Up inside the motor is a plastic sleeve that fits on where you see the hand pointing too, make sure it gets lined up and is on the housing or your going to have problems with the water being pumped up into the engine.

Installing the unit back onto the motor was the hardest part of the job, you just kind of have to wiggle things around a bit but when the splines lined up it snapped right into place, after I tightened everything up I took it out on the lake for a test and everything worked fine. I have a water pressure gauge in my instrument cluster and I watch it all the time because of all the junk that is on the river, Plastic bags will stop the water flow to the engine, if I see a decrease in pressure then I look back to see if there is any water being discharge out of the engine.

Doc Lange 6-5-2006