Intermittent raw water circulation issue -- cannot explain

[jonathanc34]

I searched, but the words used to describe this are very general terms.

On several occasions after sailing and heeling, we have started the engine only to discover the raw water is not coming out the back.

The fix is to quickly loosen the screws on the Oberdorfer pump housing, which seems to let air escape along with some water. After retightening the
screws, the pump works perfectly, water emerging happily out the back.

I also tried loosening the drain plug this time (before loosening the impeller screws), and nothing emerged at all, which surprised me. Could that indicate that the impeller was not turning?

I cannot reproduce this in our slip: every engine start works without fail.
The impeller is new; the intake filter is clean.
Sailing and heeling seem to be the variable.

Please guide my further diagnosis. :)

[Stu Jackson]

Here's a recent discussion:

https://c34.org/bbs/index.php/topic,11069.0.html

[mregan]

I'd try the sanding.  Worked instantly for me. 

[mark_53]

Sounds like the bushing in the impeller is slipping. This was the problem for me when I used the black impeller.  Switched to blue and has been working for years.

[KWKloeber]

Jonathan

The reason you can't get water out of the pipe plug is that the impeller is sealing against the body and prevents water getting from the inlet that spot (hole.)  If the intake hose is full of air it would take a long time for it to bleed past the impeller seal, if it ever did at all.  But you should be able to prime it using that hole.

You say a new impeller?  New new, or newly installed?  There were some issues with Obedorfer impellers a while back, maybe you have an old/bad one?  Is it genuine Oberdorfer, not an Amazon knockoff?

I've read a few posts about an airlock issue after heeling, but not on our C30s -- only on this forum.  The only differences I could see are a different height of the engine and distance from the intake to the pump -- although the 202M pumps are supposed to be self-priming I suppose there may be a limit to the distance as it's not creating enough vacuum to pull it?

Thinking about my particular setup, the pump supply hose swings up and runs to port a bit above the level of the thermostat before heading down to the thru hull.  I don't know if that is so on all C30s but was OEM that way on my 84.  So you might temporary try a high loop on the supply hose to see if it prevents seawater from draining out of the pump (and being replaced by air) when on heel.  I'd imagine that keeping a wet seal on the impeller would give it enough to pull from the strainer (they cannot pump air.)

[Ron Hill]

jona : From your description that the lack of water only happens after sailing with the boat heeling, pretty much eliminates the impeller, gasket as the problem.

I'll guess that you are sucking in air from somewhere in the raw water intake to the pump or the pump is loosing suction when heeling.  I'd check all of those connections and the gasket in the strainer and the bowl for cracks.  As a quick check sailing - swap strainer bowls with your fresh water system.  Again check all of your hose connections.

A few thoughts

[jonathanc34]

The inside of the pump cover was not clean: had residue from the impeller.
I cleaned and polished the cover w a series of wet sanding pads, first to remove the deposited rubber and then to polish the surface.

I confirmed that the impeller has not separated from the collar: it will not turn without the pump shaft also turning, so it appears the impeller itself is good.

When operating at idle in the slip (which was not a problem in the past), it seems to me that more water is coming out the back, so the impeller seal seems to be the most logical explanation.

Thanks for the advice, and I am sorry for creating yet another impeller troubleshooting thread. :)

[Ron Hill]

jona : Like I said your pump system is sucking in air and after heeling the "water prime in the hose" has run out of the intake hose.  Swap the raw water strainer bowl with the fresh water strainer bowel and see if the same happens!?!  As previously mentioned that bowl "O" ring gasket is SQUARE not round!!

A few thoughts

[Stu Jackson]

Ron,

It's bowl.

Please.

[waughoo]

I just replaced my raw water strainer as i was not able to locate the proper square gasket, and the o-ring kept getting dissplaced causing air intrusion.  I would suggest checking that gasket.

[jonathanc34]

I didn't have a single issue after polishing the pump housing cover: several engine starts, one after some pretty serious heeling and waves.

I have also been starting the engine with 1/4 throttle, so the pump is spinning faster initially.
Maybe that makes a difference, maybe not.

Either way: seems like everything is working properly.

Thank you all so much!

[Ron Hill]

Guys : It is amazing how polishing the pump face plate will increase the seal and pumping capability.  I've always had a couple of "fresh" faceplates in the ready!

A thought