I noticed over the weekend that the motor would run hotter than usual - 170 to 180 range during idle or low cruising. It would immediately cool down once the boat got to higher speed. I am fairly confident the impeller needs to be replace. The motor is the PCM 5.8L Pro Boss. Does anyone know what PN or brand of impeller I should be looking for? This is the one that comes up from google searches. http://www.nautiqueparts.com/sherwoodimpellerkit.aspx
That's the one. Also available here: http://www.skidim.com/prodinfo.asp?number=RP061015 I change mine annually, and also good to keep an extra on hand. Replacement's pretty easy, undo hoses, unbolt the pump from the mount on the engine (keep track of direction as it's possible to mount backwards on re-installation - sharpie an up arrow on it or remember which side of the body the hose connections are (engine side if I recall)), then split the pump open with the bolts that hold the two halves together. Swap the impeller and reassemble. If the impeller you remove is broken or missing any vanes, it's good to check where the outlet hose dumps into the engine/manifolds for those bits and clean them out if you find them. I'd also check the water strainer that's between your through-hull and the raw water pump. Unscrew the clear barrel and clean off the screen inside (they also sell replacement screens if yours is in bad shape).