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Oil slick in water

morleysd

New member
Good Evening I am new to the forum and write from the UK in some desperation ! I have a Kad 32 on a Sealine s23 which I used to love more than my Wife but not any more. I am getting a black / grey bubbly residue on the water when I throttle up or down and it looks terrible and can’t be good for the fish ! The engine starts up a treat and Idles well and seems to fly along fairly well but if you stop quickly then the black stuff appears and there is a lot of it I have had the injectors overhauled the speed sensor changed and have also had the turbo replaced so to date have spent two bags of sand (that’s two grand )
i am still none the wiser and don’t know what to do next apart from cry so any advice from over the pond would be very much appreciated The engine has done 600 hours it reaches 3400 rpm and I think it should reach about 3750 I have also had it lifted and had the bottom cleaned
I feel pretty depressed about it so need to find the love again
 

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Man, that looks nasty! I'm no diesel guy, but it looks like soot to me. I'm sure you'll hear from someone here that actually has a clue.
 
It could be your engine is passing small amounts of oil all the time, but at constant rpm the exhaust gas and water allows the oil to separate and float in the muffler, sags in the exhaust hose, and changing the rpm allows the oil to be expelled. You need to verify the engine is not using oil. You should do a compression test or better a leak down test. Bad injectors and the turbo seals (but yours have just been done) are common ways for oil/diesel to get into the exhaust. I doubt it's diesel. Also, bad valve guides, rings and head gasket can be the problem. That's why a test would help discover the problem.
Changing the throttle changes the crankcase pressure and can push oil past valve guides. Also if the engine has a crankcase breather that directs fumes into the intake. The breather can be receiving too much oil in the air, the breather filtering material can be missing or plugged with oil.
 
How much blowby are you getting and how often do you need to change the blowby filter can at the back of the engine? Is your supercharger cutting out at around 2800rpm OK? It would be a little unusual at 600hrs but some KAD32's I understand were built with inferior piston rings due to Volvo changing suppiers at one stage. Ours got to around 2000hrs before the blowby was bad enough to warrant a rebuild. Rebuilder said before even starting that the 2nd rings would be broken.He was correct. That is where I found out about the bad rings being used.
A compression test may tell you about the ring condition. The other possibility is that you are just over-propped. I think you should ideally be hitting around 3800 - 3900 light and 3700+ heavy. Being over-propped will make the engine black smoke and dump excess carbon in the exhaust system. It will smoke badly as you throttle up and then 'maybe' dump excess carbon as you slow down (not sure about this though). Are these the original props to the boat or have they been changed?
 
Many thanks for the replies. Firstly I have never heard of a blowby filter so excuse my ignorance but is there another name for that ? Secondly Re the prop size that would make sense but always had the same size and it did not used to do it so I am possibly ruling that out
the compression test I think is the next step as that will rule out a lot of nasty stuff. Someone once told me that if it starts ok which it does then that can be an indication that they are ok but I will take notice of your advice and get that done. I was also going to change the fuel filter along with the impeller to rule out the simple stuff

all advice greatly appreciated

Thanks
Steve
 
Unless your are different to ours, (might be) there is a canister filter with little holes drilled around the base up high at the back of the engine. Proper description is Volvo Penta Crankcase Breather Filter Part Number 876069. They get full of oil and gummed up then you can get increased crank case pressure. As the engine ages you will probably need to replace them more often. Not sure of the service interval but we replaced ours every year or two from memory.

Quick starting is usually a sign of good compressions, so if it is starting really well and idling smoothly you probably have decent compressions.
 
It’s not fear talk, but had a kad 44 starting fine running 3800rpm no problem.
only thing was medium blowby and some soot out the exhaust.
Opened up and all the 6 cilinders the second pistonring was in pieces.
So good starting is not to say the rings are ok.
Good luck hope it is a minor fix! Fingers crossed
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Thanks again for your replies
I found the blowby filter and it looked as clean as a whistle I then ran the engine and put my hand over the hole with it off and not much pressure at all coming from it so not sure if this is good or bad I then took off the air filter as assumed engineers had already looked at that and it was fairly dirty so have ordered that along with a new fuel filter then will as you say book it in for a Compression test !
 
If you can't feel the blowby you should be good and you will probably find good compression's. One possibility is that years of being over-propped has built up a lot of soot in the exhaust. Have you always topped out at 3400rpm or is that something new? If it has always been that way it should have been sorted out when new and had the props changed. Dropping from 3700-3800 to 3400 at WOT is quite a significant overload if it just over-propped. Are you on a shaft or a sterndrive?
 
I need to look at that prop size then without question I have only had the boat a year or so and perhaps a new set of duos went on when the broker sold it to me if the old ones had seen better days . So in answer to your question it is not a shaft draft . Quite promising that you think due to the blowby pressure or lack of it that compressions may be ok. It’s coming to winter here now so the old English Channel is not so inviting, not that it’s that inviting in the summer compared to the States so I don’t get out so much to try if but the air and fuel filter is next to do !
 
WOT = Wide Open Throttle. i.e. the throttle fully advanced
I have boated the English Channel. Used to live there in Cambridgeshire and a friend had a 52 Princess out near Harwich somewhere. Head out, go around some lightship or bouy and head back. I think we tried fishing once. Probably didn't see the best of it I guess. We lived on the banks of the Great Ouze so built a Canadian Canoe to explore that with. Very pretty. Preferred that to going on the big boat mostly.

I now live back in New Zealand and you don't want to know how nice the boating is here by comparison.
 
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