Sherwood M71 impeller replacement interval

[Todd]

I have the M71 pump on my 2004 6bt 220hp Since there is not an SMX pump for that model.

Due to Covid I am on the boat
Full time and operating the boat daily 2-8 hours usually at only 1200-1600 rpm to save fuel.

I would normally change the impeller annually with about 150ish hours, but this year will likely see many more hours than that. The current impeller was new in November and now has about 250 hours. (Impellers and new pump purchased from SBMAR)

So what change interval (time elapsed and/or engine hours) is realistic? It is always a PITA, but I don’t want to take chances with overheating.

Thanks!

Topic

[Dalton Bourne]

Boating experts recommend the best time to replace the boat impeller is every 100 to 300 operating hours or every three years. The replacement cycle for the impeller is also based on the frequency of use and the condition of the water. You have to replace the boat impeller soon if there are signs of damage or deterioration, such as melted rubber, bends, cracks, and other deformities.

[Todd]

Thanks Firehoser, I have the Sherwood pump, but the SMX brand impellers I get from SBMAR, so likely the same/similar to what you have. I found a Sherwood flyer that says change annually for light pleasure use or every six months for pleasure use at high RPM or silty water, but no “hours” recommedation. We seem to fall somewhere in the middle of those.

On my engine it is actually far easier to just change the pump and then change the impeller at my comfort and leisure, so I bought an extra pump that also makes a good backup…

Cheers,

Todd

[firehoser75]

Todd,
I know a boater who goes 2 years and approx. 1600 hours between impeller changes on a Cummins 6BTA 330 hp with a SMX pump. He states that the impellers look in excellent shape when he changes them. He travels every year from the Seattle area to Alaska and back.
Just the experience of one boater.
Myself, I just changed my (first time with a SMX pump) impeller a couple of days ago. It was 2 years old with about 500 hours on it. The impeller looked almost “brand new” (several of the vanes had a very slight bend to them). Same type of boat and same engine as the friend I discussed above.
Hope that helps.

[Todd]

Hi Tony,

Pump and impeller are new as mentioned below. So, with my current use pattern I am trying to better understand a reasonable replacement cycle for the impeller.

Thanks!

Todd

[Tony Athens]

If the pump is original (14 year of Marine Age) , then I’d be more worried about the innards of the pump itself

Cam, inner wear plate, housing ID dimensions, and the bearings in the pump..

Tony

[Author]

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