Water pump change on a Mercury 150 Black Max ????

Thread starter #1
Anyone on here ever changed one? I got a 1995 Black Max XRI,that had the alarm go off on me at the lake this past Friday,just curious how hard they are to change?Watched a few vids on youtube,seems pretty simple.


Senior Member
As a first time changer, it would be best with 2 people. The lower unit can be heavy and awkward by yourself.
1st key is put the motor in gear before dropping the lower unit. This will be crucial in getting it back together correctly.

2nd is there is a bolt under the trim tab(zinc sacrificial anode). This drove me nutz the first time, and I had a service manual to look at when I changed it.

3rd is make sure the water tube is aligned properly when you put it back together.

Depending on when it was last changed, you may only need to replace the impeller and the o-rings rather than the entire pump. This will save you a few dollars, but be sure to inspect the pump housing for any cracks.

When your alarm went off, was your motor peeing water as usual? Dirt daubers are notorious for getting in and plugging the pee hole as they build a nest.

Last, have some ibuprofen ready for your forearms after you wrestle the lower unit back in and get it bolted :) This will help your lower back, as well. Good luck!


Senior Member
I replace mine on every outboard I have ever owned. It's very simple.
1) Make sure you have it out of gear
2) remove all the nuts and one bolt toward the back. You
may have to remove the torque tab.
3) Carefully lower the lower unit until the shaft clears the
leg ( mid section). There may be a rubber tube that
needs to be removed for the speedo.
4) Remove the bolts from the impeller housing. Should be
three bolts.
5) Slide the housing off the shaft.
6) The impeller may come off with the housing. If not just
slide it off while being careful not to lose the key if it
Comes off.
8) Clean and inspect the housing and impeller base plate
which will still be on the lower unit.
9) if you see any gaulding or damage on the inside of the
housing or base plate, replace it. Also check for cracks
in the housing.
10) Slide the new impeller on the shaft.
11) Then lube the inner race of the housing and slide it
over the shaft. You may have to twist the housing
counter clockwise to get it to slide over the impeller.
12) Install the three bolts in the housing.
13) carefully slide the lower unit back up in the leg guiding
the shaft in to the hole leading to the crank shaft.
14) Make sure you reconnect the speedo tube if need be,
then if you are lucky it will slide up in place. You may
Have to help guide the tube down over the impeller
Housing. If the lower unit doesn't slide in place, have
some one to pull the kill switch and bump the starter
while you push the LU up. It will slide right in place.

15) Bolt her up and you are done! Takes me about 30min
to replace mine.

LOWER UNIT IS OUT! You will be making a trip to the dealer. The small gear changing shaft will be hanging down from the leg make sure you line it back up when reinstalling the Lower unit.