impeller 1976 20 h.p merc

[dancingwithwaves]

A steady stream of water comes out of the pee hole at high rpms and just a trickle when idiling. I looked at the impeller and it looked in excellent shape. My question is can the impeller be bad even if it appears to be in good shape?<br />Thank you for any thoughts on this problem.

 

[Laddies]

Re: impeller 1976 20 h.p merc

It's possable that the impeller had not enough tension on the blades or a set so it's not pumping well at idle, also a small vacume leak on the punp or it's pickup tube and some just don't pump much at idle

 

[Motor Boater Bill]

Re: impeller 1976 20 h.p merc

The pump is designed to work differently at low and high speeds. At low speeds it works as a displacement type pump, as the blades flex and the water between the vanes is compressed. Note that the pump housing is offset from the shaft. At higher rpm's, the blades sling the water and it works like a centrifugal type pump. If the impeller is old and hard, it may be working better in the centrifugal mode than the displacement mode. The impeller can look good, the vanes all intact, but it will not pump as well if the blades are stiff and don't flex properly, and this will be more noticable at low rpm's. Good to replace it anyway, $15 well spent.