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  1. #1
    driver0606 is offline Registered User
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    Default Turbo whistle on Cummins QSB 5.9

    Hello, The port engine on my Azimut 43 has a whistle, which I assume to be the turbo. Its not very loud, but audible in the wheelhouse. It starts at about 900 rev/min and goes when the revs pass about 1100 rev/min. No other symptoms and the starboard engine does not do it. Does this sound like trouble, please? (Oh dear, is that a pun?).
    Anyway, now the season is largely finished, there is more time for maintenance (sniff).

  2. #2
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    Quote Originally Posted by driver0606 View Post
    Hello, The port engine on my Azimut 43 has a whistle, which I assume to be the turbo. Its not very loud, but audible in the wheelhouse. It starts at about 900 rev/min and goes when the revs pass about 1100 rev/min. No other symptoms and the starboard engine does not do it. Does this sound like trouble, please? (Oh dear, is that a pun?).
    Anyway, now the season is largely finished, there is more time for maintenance (sniff).
    Rest easy, here is a SWAG (Scientific Wild Assed Guess).......Charge air cooler has a condensate drain valve, hate the things.........Located at the bottom of CAC which could simply be stuck.

  3. #3
    rafiki_'s Avatar
    rafiki_ is offline Registered User
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    Quote Originally Posted by driver0606 View Post
    Hello, The port engine on my Azimut 43 has a whistle, which I assume to be the turbo. Its not very loud, but audible in the wheelhouse. It starts at about 900 rev/min and goes when the revs pass about 1100 rev/min. No other symptoms and the starboard engine does not do it. Does this sound like trouble, please? (Oh dear, is that a pun?).
    Anyway, now the season is largely finished, there is more time for maintenance (sniff).
    Can't help with your issue, but as a fully paid up member of the Snazimut fan club, I love your boat!

  4. #4
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    Whistle is usually air leak. Look where latestarter says, and also check every connection of pipe work downstream of turbo compresser output to inlet manifold.

    Worst case could be turbo bearings, but this usually manifests itself as a whine or rumble rather than whistle. Most turbo places will change a set of bearings for a few hundred , so some money, but not real wallet bashing territory.

    Good luck!

  5. #5
    driver0606 is offline Registered User
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    Thanks guys, I will check those items out and report back (may be after Christmas, now). Interesting that it disappears at around 1100 rev/min is it not?

  6. #6
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    Yes. But, as the pressure rises, perhaps it's closing the leak by deforming hose / connector?

    I don't know how the drain valve that LS refers to works, but could it be pushed closed in the same manner?

    I would still be looking for evidence of a leak.

    For info, I have a similar problem one of my VP engines. Loud whistling on boost, followed by hissing sound if I close the throttle quickly (pressurised induction air escaping?). I have found evidence of a leak and I'm currently waiting for some new seals to arrive at my local vp dealer.

  7. #7
    rafiki_'s Avatar
    rafiki_ is offline Registered User
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    Quote Originally Posted by driver0606 View Post
    Thanks guys, I will check those items out and report back (may be after Christmas, now). Interesting that it disappears at around 1100 rev/min is it not?
    Does it disappear, or do other noises increase and drown it out? Is it a transient resonance that peaks at 1100 revs?

  8. #8
    driver0606 is offline Registered User
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    It certainly disappears and I don't think its resonance. Could well be the valve pushed closed with increased pressure. Be interesting to see what i find.

  9. #9
    rafiki_'s Avatar
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    Ok, good luck with that. Still a gorgeous boat though

  10. #10
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    Quote Originally Posted by rafiki_ View Post
    Does it disappear, or do other noises increase and drown it out? Is it a transient resonance that peaks at 1100 revs?
    Not saying 100% this is the issue, but sadly this is what happens when we get lawyers designing engines instead of engineers! I HATE condensate valves, even found yard numpty had one piped up to a stern gland wrecking a new engine.

    The fix is simple, using #1 calibrated lug hole find source of noise.

    Turbo used on QSB 425 CPL is exactly same part # as C450, way over the top turbo-machinery for application, more chance of being stuck by lightning than a turbo issue.

    As I said rest easy.

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