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Impeller Change Interval

Discussion in 'Technical Discussion' started by CaboFly, Mar 5, 2019.

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  1. CaboFly, Mar 5, 2019
    #1
    CaboFly

    CaboFly Member

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    Curious how often most change their main engine impellers. I have always done them annually. I typically see 125hrs a year on my main engines for usage. Right now on my common rail MAN's we are finishing a complete cooling system service and it got me thinking about next items on my annual maintenance list. I do oil and fuel service myself in late spring. The impeller on the Port engine is such a PIA I am tempted to consider every other year but not sure if that would be a short sighted decision or not. Generator gets impeller annually no question as it runs quite a bit more than mains.

    Wondering if others are religious about annual impeller changes or if they sometimes go every other year. Port engine water pump was fully serviced last winter 2018 and stbd pump was gone through in 2017 and fully serviced.
  2. Beau, Mar 5, 2019
    #2
    Beau

    Beau Senior Member

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    I put about 100 hours per season on my 820's. I change my impellers about every 3 years. And when I pull them they are like new. If I saw damage/wear I'd change them sooner. But for 20 seasons now, knock wood, I've never had an impeller issue. I have a dock box filled with used but perfectly fine impellers
  3. Pascal, Mar 5, 2019
    #3
    Pascal

    Pascal Senior Member

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    I think the more the boat gets used the less of a set they take. Year round use helps a lot as well

    I ve had impellers last up to 3 years and 1000+ hours on 3412s On the 84 Lazzara i run I had them replaced at 2 1/2 years and 1100 hours out of precaution because the engines are close to the bulkhead and impellers are harder to reach. They were perfect and could have gone a lot longer
  4. Beau, Mar 5, 2019
    #4
    Beau

    Beau Senior Member

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    Do you think any body opens the back plate and does an inspection? If everything looks good leave 'em in?
  5. motoryachtlover, Mar 5, 2019
    #5
    motoryachtlover

    motoryachtlover Senior Member

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    I have 820 Mans as well and I do them every 2 years. Once went 3 years and there were no issues and the impellers appeared fine.
  6. Capt J, Mar 5, 2019
    #6
    Capt J

    Capt J Senior Member

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    If I'm taking the plate off, I am changing them. I do them every 2 years or 250 hours on main engines (the large impellors, smaller mains I do every 200 hours). Now if it was a boat running a lot of hours in a short time, I'd probably go higher on the hours like say 500, but never more than that......….Generators I do annually or 100 hours. NOTHING will kill a trip more than a bad impellor, and who wants to try to change one at sea in a hot engine room and on a really hot motor. In warm water like South Florida....by 3 years they're usually very hard, cracked, or impossible to get out of the pump.....I never go 3 years, but we have year round usage here.
  7. Pascal, Mar 5, 2019
    #7
    Pascal

    Pascal Senior Member

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    I have also gotten well over 1000 on Northern Lights, Norpro and Ohnos. We put so many hours on them that hours is more critical than calendar

    Generator always let you know an impeller is missing pieces... they will stay at 180 but sound a little louder and maybe a bit of steam under a heavy load. Even then I ve gotten a few extra days.

    On a single genny boat you may not want to get to that point :)
  8. Capt Ralph, Mar 5, 2019
    #8
    Capt Ralph

    Capt Ralph Senior Member

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    Probably the cheapest item to maintain AND the most important.
    For the mains-Low hours every two years. High hours every other oil change.
    Gen-sets, every other oil change.

    This schedule works perfect four our big trip every two years.
    Yes, the main impellers are good but hard before we deploy.
    Gen-set impellers are usually gone. We rotate 2 gen-sets.

    Now outboards and stern drives, They pick up more silt and sand.
    Every year for sure.
  9. Lepke, Mar 6, 2019
    #9
    Lepke

    Lepke Member

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    I have Detroit mains and a Onan and Perkins generators. I pull mine once or twice a year. When I install, I grease the inside housing and end plate. It's that way in old Detroit manuals. I change mine every 5 years. At least 500 hours on the mains, probably a lot more. Even then they look ok, no cracks or heat damage. I save some as emergency spares. Never had a failure. The wp grease doesn't last long, but I figure it helps on the first start.
  10. MBevins, Mar 6, 2019
    #10
    MBevins

    MBevins Senior Member

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    I'm about the same on my little 6-71s.
    But I'm on the Great Lakes and I'm a good year with 80 hours. So I think that has a lot to do with it. Biggest issue is mine are a PITA to get to
    Viking did a great job packing 10# of s*"t into a 5# bag. There is zero room at that end.
  11. Capt Cole, Mar 6, 2019
    #11
    Capt Cole

    Capt Cole Member

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    I run Volvo D-6 mains and average 100 hours per year. Generally change out every 2 years. Once, I went 3 years and the impellers looked great when I replaced them. I'm more comfortable with every 2 years just to be on the safe side. I always keep the most recently removed units as spares in case I lose one.

    On my Onan gen set which has Yanmar power, I change out every other year even though it receives very light use. I'm more concerned about a loss of flexibility in the vanes.
  12. CaboFly, Mar 7, 2019
    #12
    CaboFly

    CaboFly Member

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    Thanks guys for the opinions. I was working alongside my MAN mechanic yesterday finishing up cooling system maintenance and his comments were in line with the above. On this size motor given size of impeller he felt 2 years was fine but 3 was pushing it. I will go with 2 years which is music to my ears as I just did them last spring so one less thing on my list.
  13. BoulderGT3, Apr 4, 2019
    #13
    BoulderGT3

    BoulderGT3 Senior Member

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    I changed mine on my MAN 1550's at 2yrs and 150hrs or so. They needed to changed. Some nicks in the a couple of the blades on each one.
  14. cleanslate, Apr 8, 2019
    #14
    cleanslate

    cleanslate Senior Member

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    Great post thank you all! At 100hrs per year , I'm in the two to three year on DD mains and two years on the smaller generator. And the Jabsco belt driven DD impellers always look fine.
  15. BoulderGT3, Apr 8, 2019
    #15
    BoulderGT3

    BoulderGT3 Senior Member

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    I did my Spring sea trial to check the numbers and get the baselines. The mains with the new impellers were 2° cooler with similar water and air temps. IMG_0755.jpg
  16. pupukeo, Apr 21, 2019
    #16
    pupukeo

    pupukeo New Member

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    I do not know if it is feasible in large engines, but I have seen transparent caps of impellers, would be methacrylate or something similar.
    and I found it very accurate.
    with a quick glance you had a good idea of what was inside.
  17. cleanslate, Apr 21, 2019
    #17
    cleanslate

    cleanslate Senior Member

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    That's a great idea all the pump builders should do, makes great sense ! Here that Jabsco, Sherwood , Johnson ....etc. would save on a lot of unnecessary impeller changes....but they want to sell you over priced impellers, it's a big part of their business right?
  18. d_meister, Apr 21, 2019
    #18
    d_meister

    d_meister Senior Member

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    There's more to impeller inspection than verifying the presence of vanes. Impellers can "set" to the point that the vanes bear no pressure on the bore and bypass the water instead of moving it along to the cam. One pair of 3406 Cats I worked on, had impellers that were 100% intact but weren't pumping sufficient water to cool the fiberglass exhaust, causing it to deform and leak. The vanes were permanently bent due to the direction of rotation. The vanes should be very nearly straight out axially, similar to new, to pump effectively, when inspected.
  19. Beau, Apr 21, 2019
    #19
    Beau

    Beau Senior Member

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    The see through is a good idea for day to dayquick inspections, but it doesn't tell you anything about the structural integrity. Could be skipping on its hub for all you know aside from the other problems mentioned. Change 'em every 2-3 years - heat is a diesels worst enemy
  20. cleanslate, Apr 21, 2019
    #20
    cleanslate

    cleanslate Senior Member

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    That's true , but knowing I changed the impellers recently ,it would still be nice to at lest have a visual on them with out disassembly . They should still be changed 500hr or so intervals , just my opinion .
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