Re: 150 Mariner
If you get a manual it will make it very easy, and I recommend you just follow the steps in it.
That said, here's a short version of the procedure, I'll try not to miss anything but no guarantees here, this is from memory not a manual: You put it in forward gear, scribe a line on trim tab so you can put it back where you found it, then pull the nuts/bolts that hold lower unit in place, including trim tab, and remove the lower unit. You can now see water pump - pull the bolts out, the cover off, and replace impeller and whatever gaskets and stuff come with the kit you buy, then stick it back together, making sure impeller key is lined up - it should turn with the driveshaft. Use a slight clockwise rotation on the driveshaft while putting the water pump cover over the impeller to help it go in properly. Remember to add a little grease to driveshaft splines but NOT the top of driveshaft, then put lower unit back on. ***When you put lower unit on be very careful to line up the water pump tube*** -otherwise if you don't water won't flow to powerhead! Make sure it goes all the way up BY HAND and when it does put nuts/bolts back in, line up trim tab, check that it shifts properly and go on your way. FYI- now is a good time to change the oil in the lower unit if you haven't already.
Hope that helps.
