Turbo whistle on Cummins QSB 5.9

[driver0606]

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).

 

[Latestarter1]

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.

 

[rafiki_]

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!

 

[rosssavage]

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!

 

[driver0606]

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?

 

[rosssavage]

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.

 

[rafiki_]

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?

 

[driver0606]

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.

 

[rafiki_]

Ok, good luck with that. Still a gorgeous boat though

 

[Latestarter1]

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.

 

[burgundyben]

even found yard numpty had one piped up to a stern gland wrecking a new engine.

Ooooof!

 

[driver0606]

Hello,
This is an old thread now but I said I would report back and its only recently I started running the boat again. Well it seems Latestarter1 was right (again) as I found a strange looking shiny outlet at the base of what I presumed to be the charge air cooler (easy to see why somebody would think it needs a hose on it). I carefully poked a wire up the hole, which did not go very far. The whistle seems to have gone. Thank you for all your comments, including your kind words about Azimut, Rafiki. Well, we all like to hear nice things about our boats do we not?
Wishing everybody a great season,
John.

 

[rafiki_]

Hello,
This is an old thread now but I said I would report back and its only recently I started running the boat again. Well it seems Latestarter1 was right (again) as I found a strange looking shiny outlet at the base of what I presumed to be the charge air cooler (easy to see why somebody would think it needs a hose on it). I carefully poked a wire up the hole, which did not go very far. The whistle seems to have gone. Thank you for all your comments, including your kind words about Azimut, Rafiki. Well, we all like to hear nice things about our boats do we not?
Wishing everybody a great season,
John.

Good result John. Latestarter is a serial admirer of the QSB engines, so I'm quite confident that they will give many years of reliable service assuming correct maintenance. I have an earlier Snazi 39 with the Cat 3126 engines.