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  1. #1
    Join Date
    Nov 2017
    Posts
    71

    Default Black Exhaust discharge

    My boat has a 40yr old Volvo penta md5 it's fairly clean and been well cared for. But when I run the engine too hard (there's no rev counter) I get a black coloured slick in the water behind the boat. I dont think its diesel because it doesn't give the rainbow colours you get when spilling fuel. Could it be oil? Although I dont seem to be losing any? Only other though was maybe it's carbon from exhaust been blown out?
    I'm not a mechanic engine runs great and starts well too. Just worried it might need work doing.


    Thanks

  2. #2
    Join Date
    Oct 2009
    Location
    Home; Abingdon, Oxfordshire. Boat; Hardway, Gosport
    Posts
    3,966

    Default Re: Black Exhaust discharge

    Have you antifouled and cleaned your prop this season?

  3. #3
    Join Date
    Nov 2017
    Posts
    71

    Default Re: Black Exhaust discharge

    No not yet she was ashore in June last year. I think it was doing it when the hull.was clean too

  4. #4
    Join Date
    Jun 2013
    Location
    scotland
    Posts
    135

    Default Re: Black Exhaust discharge

    Does it have a cold start lever you pull out for cold starts? If so make sure it is returning fully down at the pump after the engine starts. Depends on how hard you are running the engine. Full throttle operation especially if you are still tied to a pontoon is going to cause black smoke. At what point on the throttle travel does the black smoke start?

  5. #5
    Join Date
    Nov 2017
    Posts
    71

    Default Re: Black Exhaust discharge

    Hi black mercury. It does have a cold start and I should check it returns fully. It's only.when the throttle is opened up that it creates the black slick. But its definitely not smoke I get a little white steam/smoke.but.nomther colour the black.slick is in the water

  6. #6
    Join Date
    Oct 2004
    Location
    somerset
    Posts
    223

    Default Re: Black Exhaust discharge

    If it is any help, I have found that when my propeller has been fouled with weed the boat may only do 3 knots even with the throttle wide open. Looking over the stern, I have seen black soot like deposits from the exhaust in the water. Effectively, the weed is preventing the engine turning fast enough to properly burn the fuel. Once the weed is cleared all is well again.

    Assuming the boat was not bought new by you and that there is no excessive fouling of hull and prop, I suggest the possibility that either the fuel system is delivering too much fuel or perhaps a slightly oversized prop was fitted before your ownership.

    I should say that I am not a mechanic so my advice is intuitive rather than from authority!

  7. #7
    Join Date
    Jun 2013
    Location
    scotland
    Posts
    135

    Default Re: Black Exhaust discharge

    Quote Originally Posted by Teko View Post
    Hi black mercury. It does have a cold start and I should check it returns fully. It's only.when the throttle is opened up that it creates the black slick. But its definitely not smoke I get a little white steam/smoke.but.nomther colour the black.slick is in the water
    Yes, check the cold start lever on the engine springs back after you start engine and the revs increase. Just because you push the hand lever in don't assume the lever on engine has returned. It should, but may need encouraged with a tap!

  8. #8
    Join Date
    Jul 2002
    Location
    Home: Kent. Boat: Chichester
    Posts
    43,057

    Default Re: Black Exhaust discharge

    Quote Originally Posted by Teko View Post
    Hi black mercury. It does have a cold start and I should check it returns fully. It's only.when the throttle is opened up that it creates the black slick. But its definitely not smoke I get a little white steam/smoke.but.nomther colour the black.slick is in the water
    If it starts easily, runs well and does not use excessive quantities of lube oil dont worry about it unless it starts to produce clouds of black smoke.

    The injector probably just needs cleaning/ servicing. Has it been done every 3 years as specified in the manual ?

  9. #9
    Join Date
    Jul 2006
    Posts
    4,655

    Default Re: Black Exhaust discharge

    Seen this many times on old Volvos, apart from the sooty water engines running well and reliably. As VicS says, possibly a poor injector spray, maybe too rich.

  10. #10
    Join Date
    Nov 2017
    Posts
    71

    Default Re: Black Exhaust discharge

    Thanks everyone doesn't sound too serious then. Plenty to think about with the above info! I'll report back with what I find

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