Generator losses raw water prime.

[Pmcsurf1]

I've got a Onan (Kabota I think) 8KW MDkD. Runs great but raw water won't self prime to the water pump. Water level is a couple inches below raw water pump. I have to run shop vac to discharge hose , at the mixing elbow. Start engine and when water flows into shop vac attach hose back to mixing elbow.
I've replaces raw water impeller twice. Can't find water leaks anywhere. Once primed it's fine. If I start the genny next day, it's fine. If I move locations and start genny next day... not fine. Shop vac again.

 

[Turtle Blues]

Is this a recently occurring problem or has it been long standing?
For first instance would be searching for loose hose connection, impeller plate seal failure or similar allowing air to seep in and break connection.
If long standing, rerouting supply hose to provide some type of loop to maintain sufficient water in pump to overcome on startup. This is the second option, would rule out all other possibilities before modifying.

 

[Bmarler]

I would second the pump as suspect. A worn cover or end plate, possibly a shaft seal, but that would likely show as a leak.