Onan genset – no water flow. Tried everything I can think of.

[Nicholas]

I’m not getting any raw water flow through my late 80s vintage 8.5kw genset and am out of troubleshooting ideas. Hoping for some suggestions.

The problem started when the boat yard put the handle on my intake sea cock 90 degrees off after servicing the through hulls, resulting in me starting and running the genset with the seacock closed. It ran for about 10 minutes then the fault breaker tripped.

Once I figured out what was going on, I checked the impeller and it was fine but I changed it anyway.

Started it up again and no water after running about 90 seconds. Turned it off.

Removed impeller cover, bumped the starter, and verified the impeller spins.

Paid more attention to making sure raw water was up to the level of the pump, put some more Dawn in the pump, pulled the sea water hose of the exhaust mixer and filled the raw water system completely with water.

Started again, still no water flow.

Removed both hoses from the pump and disconnected the raw water hose from the exhaust mixer. Flowed fresh water “backwards” from the mixer hose out through the pump outlet hose, then “forwards” via the same route.

Verified water flows through sea strainer unimpeded through pump inlet hose.

Poured water into exhaust mixer and verified no apparent obstruction in mixer.

Put everything together, primed as before, still no water flow after 2-3 minutes of running.

Drained everything, removed heat exchanger. No visible blockage or growth whatsoever. Soaking it in barnacle buster now for good measure. Changed zinc – old one was in good shape with no sign of any pieces having broken off.

I’m totally flumoxed. Only thing I can think of is that the pump is bad. Is it possible that the pump would fail in such a way such that the impeller would turn with the cover off, but not with the cover on or otherwise not be able to pump water?

Other suggestions?

Topic

[Tony Athens]

2 things for now…

The internals on the pump housing are worn to where you are not getting a good suction– Cam, inner wear plate, back plate, and the housing ID.

Pull the impeller and coat the inside of the housing, back late and the impeller with COMMON wheel bearing or lithium grease —TRUST ME–Be copious with the grease.. If it primes, you need a new pump and it’s out of tolerance (30 years of Marine age) , or you have a suction leak.

[Rob Schepis]

Are you positive that the seacock valve isn’t faulty? Are you sure it is not damaged and that moving the handle is actually not opening the valve? If you remove the seawater hose from the inlet side of the pump and open the valve you have good flow?

[Author]

Replies