Losing the prime on raw water pump

[mseamster]

I have a M-25XP with an Oberdorfer raw water pump. Recently, I changed out the impeller (used the black one not the blue one) and changed the seals on the shaft. Since then, I am experiencing an intermittent problem where we start the engine and no water comes out the exhaust. The "fix" involves disconnecting the hose on the inlet side of the pump, and sucking water up the hose from the the thru-hull/strainer. Yes, like siphoning gas from a car's tank. We then reconnect the hose to the pump, and everything is cool (pardon the pun). This does not happen on every start, but it happens often enough to drive us crazy. Any ideas?

 

[Stu Jackson]

Faceplate. Either sand the inside face or get a new one. If you look at it I'll bet it's scored.

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[Stu Jackson]

You could also have a clog in the intake thru hull. If it's soft, blow it out with the dinghy foot pump from the rw pump inlet. If it's a hard barnacle, you may have to get in the water. Take the rw strainer off to see if you have flow.

 

[kloudie1]

Hey, MSeamster.. Flattening the cover plate was on the list to do with the new impeller..I couldn't make it over yesterday.. The plate has enough wear to make it need flattening.. Should be done by getting some good 100 grit sandpaper and putting it on something really flat that will not deform with pressure.. a granite countertop or a glass plate .. put the faceplate on the paper and swirl the plate in small circles while making a bigger circle with the swirls. try to put even pressure on the outer part and every now and then rotate your hold to even the pressure on the plate. Do that until the plate is contacting the paper all the way across.. next use 400 grit wet paper and do the same thing until all the marks from the 100 grit paper come off, and the plate is flat and shiny all the way across .. Should help the pump to prime better and more consistently.