HX / Oberdorfer pump - faulty impeller

[David Sanner]

I just updated the wiki but figured I add my recent experience here.

I noticed yesterday there was no water pumping out of the exhaust.  Quick check of the impeller and it looked fine.  I cleaned the strainer, pulled the hoses and all seemed clear yet it still wouldn't pump.  I popped in an old globe blue impeller and all was well.  Did I miss something?  Slightly worn profile w/ cover plate groves the cause?  Seems like I would still be getting some water as I primed the lines, etc.

Doing some head scratching at home today with what looked like a perfectly good impeller I noticed the metal portion that is keyed to the shaft was more or less free spinning inside the rubber impeller itself.  Poor design I would say as it looks like more of a friction fit between the metal and the rubber. 

Anyway... a simple heads up when doing an impeller check as I'm sure I'm not the first or the last w/ this issue.

[Ron Hill]

Dave : Looks like an old impeller that finally had the metal to "rubber" bond fail!!

A thought

[waughoo]

I believe I have seen this mentioned before David.  It is an excellent reminder though as I think if I looked in my pump and saw all the vanes standing out proud and no cracks that I would be a little stymied.  Thanks for the post.

[scgunner]

David,

As Alex mentioned this thread has popped up before. It happened to me a couple years ago, same thing no exhaust water. On examination the bond between the rubber and brass had failed so the brass was spinning inside the rubber. My impeller had only a few hours on it. First time it's ever happened since I've owned my boat ('88). The thinking was possibly a different supplier. In any case it's always a good idea to have a spare and the ability and tools to change it on the water.

[David Sanner]

This was the impeller that came w/ my new water pump I bought years ago (after rebuilding the previous one and having it leak again).  I've rebuilt my new water pump a few years ago and w/ a clean HX no dripping.  As others have mentioned making sure there is no build up on the seawater inlet side of the HX is key to lower pressure / dripping.

I believe this this impeller was just too old though it sounds like it can happen at any age.  I'll say again - bad design.  Seems like they should have some splined/keyed texture on the outside of the keyed core.

Back to my old trusty run dry blue globe impeller. 

Time to find a good source for a spare (current spare is really old).

[Ron Hill]

Dave : I've given up on the black impellers and strictly use the blue Globe!!  Have NEVER found a crack at the base of a Globe vane like you do with a black impeller!!

A thought