Alpha waterpump housing possible cause of no cooling water flow?

[crazy charlie]

1988 5.0 rwc Mercruiser with Alpha one drive.Last spring, Did a waterpump service.Ran at idle at home temp was fine.Launched and idle speed to slip 10 mins running ,temp fine. Next start up Ran at idle in slip a week later and temp spiked.Checked water flow and nothing.Took home and ran on muffs ,no water flow.Pulled drive and split drive. Impeller and internal housing looked brand new .Got a new kit and Compared new housing to current one and Noticed that the water tube in housing was sitting deeper in the new housing as noted in the clean section of water tube in pic.There seems to be a rubber grommet missing where the water tube seats in the top of the housing.I am assuming this is why the water flow was interrupted .I place a garden hose in upper and water flow was fine.I poured water into the impeller plate and it flowed out the intake vents fine so no obstructions in upper or lower.Backflushed power steering cooler with good water flow. So I am assuming the water tube sitting deeper in the housing with the missing grommet did not allow a good seal to pump water thru upper half of the drive.Done my waterpump service for 30 year and never encountered this.Hope I got to the bottom of this.Charlie

 

[crazy charlie]

I confirmed by inspecting some old housings that I had kept (I always hang on to old parts for comparison sake) that there was indeed a grommet missing in my waterpump housing causing the water tube to sit a good 1/2 -3/4"inch lower in the top of the housing than it should. I never thought of checking that upon installation in my 30+ years of doing my waterpump service. I should do a post about that with a warning for others. So my summation is that with the missing grommet and the water tube sitting too deep into the housing that there was a gap in water flow from the lower to the upper.Charlie

 

[Chris1956]

Usually the top and bottom of the copper watertube seal against those gromets. They last longer then the impellers, so they often get overlooked.