Raw water pump wont pump

[NETriton]

The raw water pump on my A4 is what I believe to be a Sherwood "30G" -- 6 bolt pattern with the words "Sherwood Detroit" stamped on the brass.

I got the A4 running (its on the hard still), but now the water pump does not seem to have suction. The pump is belt driven off the crank pulley (spins great, new belt) and I have changed the impeller, and ensured the keyway is correctly installed, etc. I should note that the pump was excellent all last year.

I have tried putting the intake hose in a bucket AND have set up a toilet plunger hose contraption on the through hull outside -- but no matter which method I use, the pump does not want to pump water and the engine quickly overheats.

I dont think there is a clog anywhere, because at one point yesterday when I had her running she WAS pumped correctly (I cannot remember if this was before I changed the impeller or not, but the new impeller is the exact same brand).

My guess: the pump is sucking some air --- I used the flimsy paper gasket on the back of the water pump, but maybe I should use some gasket sealant as the surfaces may not be perfectly sealed?

OR -- does the pump need to be "primed"?

Thanks all

[Dave Neptune]

First check

Check the "width" of the impeller closely, if it is not exact and just a bit narrower it won't pump.
Is the water contraption fed by a hose? If it is there should be no need to prime.

Dave Neptune

[NETriton]

Thanks Dave, I thought of that (I understand this was an issue with some of the Oberdorfer pumps, as indicated by the threads on the subject) but considering the old impeller was new mid-summer last year, I cant imagine there is any difference between the two.

Yes, its fed by a hose.

Im putting my money on a bad gasket seal / air leak but I will troubleshoot when I am back on the boat tomorrow.

[Dave Neptune]

Ok

If you have water pressure feeding the pump I'd suspect a blockage, perhaps in a strainer or a closed valve.

Dave Neptune

[NETriton]

Because it had worked at one point yesterday, and I know I didnt lose any impeller fins, I suspect a blockage is unlikely, but I will keep at it

[NETriton]

I seem to have fixed it --- took off the bronze pump plate, polished it well, and sealed it with gasket sealer --- pumps great now! Must have been leaking air.

[JOHN COOKSON]

NET: Keep An Eye On This

The threads may be bunged up and the only thing holding the seal is the gasket sealer.

Check for tightness every once in a while to be sure the engine vibration doesn't shake something loose as far as the seal goes. You may need to chase the threads.

Was water leaking out of the pump?

TRUE GRIT