Raw Water Pump won't prime

[Brian N]

1996 Volvo Penta 3.0GS IO

The boat is new to me so I have been doing some preventive maintenance.

Changed out a few hoses, thermostat, water pump impeller and water pump cover gasket.

Before changing anything the pump was strong, drew and pushed plenty of water. Now it will not prime!

If I remove the intake hose, fill it with water and reconnect it she pulls water just fine. But when on the muffs it will not prime itself even with solid water pressure. I also put her in the lake and fired her up to see if maybe there just wasn't enough water from the hose but still no luck.

If I hold the muffs on tight it will force the water up through the system, so there does not seem to be a blockage.

The impeller is definitely installed correctly and is the right impeller. I even tried putting the old one back in since it was in good shape and had the same problem.

I then took the water inlet hose off, filled it with water, and put it in a full bucket next to the engine...Voila! She pulled the water in just fine. Put the hose back on and try again with the muffs and hose, nothing...

HELP????

I know I'm overlooking something simple and it's driving me nuts!

 

[Sandy]

Sounds like the RW pump cover seal (O-ring?) is letting air in. Check that seal.
Air is much easier to suck in than water but once water seals the blade tips to the wear surfaces of the pump it will draw water.

If you hadn't mentioned it worked fine before the impeller change I would have guessed the pump wear surfaces were scored or impeller was bad. (Scored housing or impeller blade tips won't draw at idle when the blades rub the wear surface but can still pull/& mostly push water fine at higher rpm when blade tips are not touching the housing.)

But you may need another impeller if run without it sucking water.

 

[Riverratt]

Muffs can be a problem. Try dumping liquid soap and water in the intake side.

 

[Golfman25]

sounds like you have an air leak somewhere. Tighten everything up.

Welcome back to boating.

 

[j-d]

Of course there's a hose from the inner transom assembly to the engine. There's also a hose or fitting between the gimbaled part of the outdrive and the outer transom assembly. This hose allows the outdrive to steer left and right and trim/tilt up and down. Those same motions can also damage the hose.

 

[jtybt15]

My guess would be what Golfman said. Most likely intake side somewhere. Is RW pump below water line? Pump 'OUT' hose should be full of water. What side of pump are the oil coolers?

 

[Brian N]

So I never quite figured it out, but I got it fixed. The guy I bought the boat from had a spare water pump from an engine he had torn down for someone else. He gave it to me to try. I just finished putting it in and it pulls fine...

To follow up on the old pump, I had changed the impeller as well as the gasket, both came with the kit. I checked all hose clamps and hoses as best I could, no air leaks that I could detect. I'm wondering if the shaft seal on the old pump is gone. I may send it out for rebuild and then replace this pump with it. i don't know how old the one I just put in is, but it works for now and therefore we can enjoy some time on the water...