Bad impeller? What am I missing?

[hcalmar]

Engines ran fine durring commisioning trial this year. Changed the Jabsco impeller #17936-0001 on my 671 TIs just like I have in the past. Starboard went fine. Works. Replaced port, started up, cover plate and pump got super hot, no water. Took it apart 2x put it back together same issue. Took it out and put in the old one and it works fine! It is the right # and dimmentions to the eye. Turns in place obviously or it wouldn't be getting hot. I am baffled. Maybe it spun the hub like a prop and turns enough to get hot but no water?
Hal

 

[Jaxfishgyd]

If the new one causes the housing to get super hot, but the old one does fine, it has to be a defective/wrong new impeller....

 

[REBrueckner]

17936-0001 is the impeller with the spline type shaft fitting....I assume the splines on the impeller fit ok or you'd see they are stripped....

that seems to leave the metal impeller hub NOT fastened to the impeller blades....maybe a manufacturing defect??? I'd stick an ice pick point, or small screwdriver or knife point between the metal impeller hub outer circumference and the impeller synthetic...see if you can push the ice pick in and determine if the impeller parts are rotating separately...

 

[Daybreak]

That happened to me once. I had to throttle up to get the water flowing again properly. Idle RPM wasn't enough to prime the system and get it flowing again.

Ben

 

[REBrueckner]

Did you prime the pump with some water..via the zinc plug or other access???

 

[hcalmar]

No I did not prime. Never have. ??? Now that the housing got so hot (although the impeller looks fine) should I avoid using it?

 

[REBrueckner]

I notice when my mechanic launches boats he never primes raw water pumps either...I also asked and he confirmed that.

But I always do....Even if you just loosen the zinc plug, you'll feel,,, and can hear if things are quiet,,,, air push out as water comes in the system to waterline level...so even that gives you a slight reduction in dry run time. My main engine water pumps were definitely above water line as water never ran out the zinc plug connection.

Another option is to wipe the impeller tips or pump housing with something like dawn liquid during installation...or a touch of grease .......that helps lubricate the blades until water is picked up.

I was already wondering what I'd do with the impeller involved with overheating. I think I'd keep it as a spare......All I can think of is to buy a new one, and carefully compare the appearance and flexibility of new versus "hot"....if you can't tell any difference maybe it's ok. The other argument is" look, man, for $60 do you want to risk an impeller failure when you are out running??"

 

[jim rosenthal]

I'd throw it out, or return it for another one if you can. I also use Dawn or something like it when I start the engines after I've changed the impeller. You might also look at Globe impellers, which can run dry briefly without damage.