Re: 1988 Johnson 15 HP need to replace the Water Pump???
Super common question around here, but first run a weed wacker string up the rubber hose and make sure it's not clogged by bugs or sand. If that doesn't fix it, it's easy to drop the lower unit and change it out. There are three bolts on each side of the lower, remove those, then shift the motor into gear so the lower unit drops down. Then remove the top bolt of the shift linkage, be careful because it's all that's holding the motor on at that point. Pull the lower unit off and you should see where the driveshaft goes into the lower unit. The plastic housing contains the impeller and it should be straight forward from there on how to change it.
