Exhaust oil under boost

DrumBeat

DrumBeat

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Guys I’ve taken the boat out today,
As soon as I increase the revs to 2300, turbo kicks in and the revs keep bogging down and picking up again. Today, I noticed that there’s a trail of black coming out from one of the exhausts only under boost!
I also can’t get the boat over 25knts at full revs anymore when it should do 32+

I’m assuming this is all linked to turbo wear? Hopefully that’s all it is. One turbo replacement isn’t too painful on the bank balance.
 
is It a sudden thing? Was running fine….now not?

When you say turbo kicking…..do you mean supercharger?

Dirty bottom…props would be my first thought
 
Well I’ve just jumped in and checked underneath and it’s just a bit fluffy on the hull, props are pretty clean. Just scrubbed them again.
it’s not the supercharger no it revs fine until turbo kicks in and then the revs keep bogging down and picking up… it’s a mystery at the moment.
if it was oil wouldn’t it be Smokey?
 
Black could be overfueling due to lack of air. Air leak, dirty intercooler, stuck or worn turbo…take your pick.

Hard to know as,you haven’t said if it’s sudden or been a growing issue. when last used etc…

Make sure the intake flap isn’t stuck too
 
Mr Googler said:
Black could be overfueling due to lack of air. Air leak, dirty intercooler, stuck or worn turbo…take your pick.

Hard to know as,you haven’t said if it’s sudden or been a growing issue. when last used etc…

Make sure the intake flap isn’t stuck too
Click to expand...

well it’s been used regularly over summer, there’s been an issue with the revs dropping as soon as the turbo kicks in for a while, we thought it was the fuel so we changed the fuel filters but hasn’t sorted it.
it seems to have gotten worse and today we noticed a little black trail appearing in the sea behind us
 
volvopaul said:
Worn turbo , as the SC cuts out the boost drops because the turbo housing is worn , you have low boost from the turbo that’s why it’s cycling in and out .
Click to expand...

Thanks Paul,

Is it unusual for this to happen to two turbos at the same time though? It seems odd that they’ve both started going simultaneously.
Is there an easy way to confirm this? i guess taking the exhaust elbow off and inspecting the fan for play?
 
It’s usually one , you get hesitation eg runs swimmingly at 3200 both humming along .Then one drops to say 3000 and a few sec or later more seconds it recovers until the next time .The frequency increases and the rev drop deepens .
If the effected one drops really deep into the turbo / SC transition zone ( about 2800 / 2900 rpm on KAD 300s ) the good engine can’t cope pushing the boat all on its own so is kinda dragged down .In my experience it cant continue to shove 9 tons of Sunseeker at 26 knots so it goes into temp overload mode and the boat and that motor slows .
Once the bad ones finished with its hissy fit it starts to make a contribution and the good one recovers they both sing away at 3200 rpm and the speed recovers No ones touched the throttle btw …….until the next time .

Its the air gap between the fan and its housing that increases loosing boost .
That what you need to look for .

Yes the bearings fail like any turbo but once failed they stay failed they don’t suddenly re start to spin up to 100000 rpm ,
Aside a finger spin is meaningless unless it’s ceased .But it ain’t .
 
Portofino said:
It’s usually one , you get hesitation eg runs swimmingly at 3200 both humming along .Then one drops to say 3000 and a few sec or later more seconds it recovers until the next time .The frequency increases and the rev drop deepens .
If the effected one drops really deep into the turbo / SC transition zone ( about 2800 / 2900 rpm on KAD 300s ) the good engine can’t cope pushing the boat all on its own so is kinda dragged down .In my experience it cant continue to shove 9 tons of Sunseeker at 26 knots so it goes into temp overload mode and the boat and that motor slows .
Once the bad ones finished with its hissy fit it starts to make a contribution and the good one recovers they both sing away at 3200 rpm and the speed recovers No ones touched the throttle btw …….until the next time .

Its the air gap between the fan and its housing that increases loosing boost .
That what you need to look for .

Yes the bearings fail like any turbo but once failed they stay failed they don’t suddenly re start to spin up to 100000 rpm ,
Aside a finger spin is meaningless unless it’s ceased .But it ain’t .
Click to expand...

Would this cause oil to come out of The exhaust while it’s happening? ( There’s some sort of brown liquid coming out the back whilst the engines bog down)

Portofino said:
It’s usually one , you get hesitation eg runs swimmingly at 3200 both humming along .Then one drops to say 3000 and a few sec or later more seconds it recovers until the next time .The frequency increases and the rev drop deepens .
If the effected one drops really deep into the turbo / SC transition zone ( about 2800 / 2900 rpm on KAD 300s ) the good engine can’t cope pushing the boat all on its own so is kinda dragged down .In my experience it cant continue to shove 9 tons of Sunseeker at 26 knots so it goes into temp overload mode and the boat and that motor slows .
Once the bad ones finished with its hissy fit it starts to make a contribution and the good one recovers they both sing away at 3200 rpm and the speed recovers No ones touched the throttle btw …….until the next time .

Its the air gap between the fan and its housing that increases loosing boost .
That what you need to look for .

Yes the bearings fail like any turbo but once failed they stay failed they don’t suddenly re start to spin up to 100000 rpm ,
Aside a finger spin is meaningless unless it’s ceased .But it ain’t .
Click to expand...

This is very informative thank you!

although, when I increase the power to full, the turbos boost again and engine runs fine. Although, they do struggle to reach full revs and speed, they sit at a max of 3100rpm now for 20 - 22knts
 
Last edited:
Could be over fuelling of the ones that dragged down or the one with the sudden weaker turbo .
Depends on the level of electrotwackery it’s got running it .
Not a great amount considering the age ?
 
Not a lot I wouldn’t think.
Its suffered from a serious diesel bug problem previously so I’m wondering if that could cause anything? Possibly gunk getting through the fuel line? Although I don’t see why that would only affect it when the turbo spools up.
I did drain a lot of grey muck from the racors the other day….
 
DrumBeat said:
Not a lot I wouldn’t think.
Its suffered from a serious diesel bug problem previously so I’m wondering if that could cause anything? Possibly gunk getting through the fuel line? Although I don’t see why that would only affect it when the turbo spools up.
I did drain a lot of grey muck from the racors the other day….
Click to expand...
Arh now you have just overlayed another problem .
Maybe when asked to spool up the fuelling struggles to keep up ? So it all drops back .
The fuel thing needs first sorting obviously.
 
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