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Westerbeke Genny eating impellers

Discussion in 'Generators' started by Bayhouse, Oct 1, 2026 at 5:31 PM.

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  1. Bayhouse, Oct 1, 2026 at 5:31 PM
    #1
    Bayhouse

    Bayhouse New Member

    Joined:
    Oct 11, 2020
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    Location:
    Brigantine, NJ
    I have a ~2005 Westerbeke 8.0/6.0 BTDA generator that I've had to replace the impeller 2x (all new Westerbeke) in under 2 hours of use. Important details:

    1. There is a single sea chest for the main engines (C12's) and all other thru-hulls including the generator.
    2. All broken parts from each impeller have been recovered from the cooling system.
    3. The strainer is clean and I've run fresh water thru the hose from the strainer to the genny impeller housing - no blockage. The hose from the strainer to the generator is new.
    4. I've backflushed the line from the genny housing thru the strainer and out the sea chest - the last time for about 20 minutes at full volume - there is no back pressure.
    5. The bottom of the boat is dirty, she's sat at the dock since June.
    6. Generator starts fine and pumps water strong with and without the mains at idle.
    7. I did notice that the impeller housing appears to be "polished" but maybe that's normal when the water supply is cut off and the impeller begins to deteroriate.
    I realized that one impeller likely burned up because I bumped up the RPMs on the mains (in neutral) sitting at the dock and I'm guessing that the increased demand from the mains likely starved the generator supply - does this make sense?

    Another one went after a soft grounding and I needed to increase RPM's on the port engine only (deeper water) to get free of the bottom. The wash from the prop would have been blowing over the sea chest and again, given the demand from the main engine - and sitting still like at the dock - could have starved the generator supply too??

    I suspect there's some growth in the sea chest as well, but the generator (and all other pumps) run fine otherwise.

    The boat is scheduled for haul out and cleaning in 2 weeks, just want some outside in perspective about what else I should check.

    Suggestions?
  2. Pascal, Oct 1, 2026 at 7:30 PM
    #2
    Pascal

    Pascal Senior Member

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    Unless the sea chest is grossly undersized, I can’t imagine the mains preventing the gen from getting enough water.

    I sounds like you have some crap inside the sea chest or at the sea chest inlet on the hull. Have you dived to check it ? I woudl start there
  3. Capt Ralph, Oct 1, 2026 at 7:35 PM
    #3
    Capt Ralph

    Capt Ralph Senior Member

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    Location:
    Satsuma, FL
    Ah, Gen-set impeller fail school 101.
    Raw water impellers fail because of water restrictions to the pump. Gobbles of causes here.
    Raw water impellers fail because of water flow restrictions after the pump. Gobbles of causes here.
    Raw water impellers fail because of impeller age, in the machine or dust collecting on a shelf some where.
    Raw water impellers fail because of improper installation and improper priming.
    Raw water impellers fail because of improper installation and leaking gaskets & seals.
    Raw water impellers fail because of worn internal surfaces in the ridged pump housing.
    Raw water impellers fail because of air leaks in common sea-cheast.
    Raw water impellers fail because of poor location (at or above sea level) in a sea chest.
    Raw water impellers fail because of it's attached to a WesterBroke gen-set.
    What was the last service before you started eating impellers?
    What environment has changes since last reliable operation?
    Laurence C likes this.
  4. Capt J, Oct 2, 2026 at 12:45 AM
    #4
    Capt J

    Capt J Senior Member

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    You have a restriction on the other side. I chased this problem and dollars to donuts the heat exchanger was mostly clogged causing a ton of head pressure, this in turn made the impeller polish the water pump housing because of cavitation.

    If the a/c seawater pump draws from the sea chest, get it off of there on it's own thru hull immediately.

    They aren't knick named Westerbroke for a reason because they'll keep you alwaysbroke.
  5. Bayhouse, Oct 2, 2026 at 8:53 AM
    #5
    Bayhouse

    Bayhouse New Member

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    Location:
    Brigantine, NJ
    The boat was designed with the sea chest and with over 2k hours, I think the sea chest approach is fine - could it be better with a thru-hull, sure but that's a project I'll consider later.

    She ran to/from Florida and NJ last year and in the spring and was flawless over that time. Problems started after she sat at the dock unused for an extended period.

    This seems like a good place to start, the volume of water seems to start strong but then weakens a little as time goes by. Checked my logs, the HX was installed new in 2022 and I'm ashamed to admit, I haven't done anything to it since. Should have had that done when the mains were serviced. I'm going to pull that and get it cleaned,

    Thanks for the fast responses!
  6. Pascal, Oct 2, 2026 at 12:27 PM
    #6
    Pascal

    Pascal Senior Member

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    Has to be crap inside the sea chest. Growth or it could even be something like a plastic bags that got in there and got trapped at the gen inlet thruhull.