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Anti-siphon loops on exhaust sea water supply.

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  • #75908
    Richard Proud
    Participant

    Hello, I have a 1984 Nauticat 38, The original ford engine failed and a second hand iveco has been installed by a marine engineer. I have now found indications of water in the oil. It turns out that the engineer, without consulting me, has not reinstated the anti-siphon loop on the water supply into the exhaust. He said it is unnecessary. The Nauticat manual says it is necessary and I assume it was originally included for a good reason.
    Can anyone offer any advice?, could the water in the oil be because of the missing anti-siphon loop and even if not, should I reinstate it?
    I am investigating having the oil analysed for seawater to see if this sheds any light on the subject, any comments?

    #75909
    Bill Clark
    Participant

    I can’t see how the missing siphon-loop could possibly be responsible for water in the engine oil. Yes, you should reinstall it.

    #75910
    Gordon Paterson
    Participant

    Anti-siphon is essential. Serious damage may already have been done as water siphoned back up through the exhaust and into the cylinders through the exhaust valves. I think that you will find that it is salt water in the oil.

    #75911
    John Skidmore
    Participant

    As it was a second hand engine, it seems highly likely that the cylinder head gasket has failed, or worse, I’m not familiar with that engine but if it has wet cylinder liners then the water seal on the liners could have gone. Which all points to the engine having been “ cooked” at some time in the past, I agree that the lack of a siphon shouldn’t compromise the oil unless it was very serious and water had got back into the cylinder head and an attempt to turn the engine over had been made.this is unlikely to be the case as you would have ended up with a cracked block! John Skidmore

    #75914
    Richard Proud
    Participant

    Thank you all for the opinions.
    Can anyone say with clarity why the anti-siphon loop is required and the consequences of not having it? I just want to have something definitive to challenge the engine installer with.
    Best regards, Richard Proud.

    #75915
    Bill Clark
    Participant

    The purpose of the siphon break is to prevent a siphon been established: on my Nauticat the siphon break is on the exhaust side of the engine – it will stop a siphon forming in the exhaust system (which could in theory form if water enters the exhaust due to wave action or heeling when the engine is not running). The danger is that a siphon could allow water through the exhaust all the way through the exhaust valves and into the cylinders. Although this is highly unlikely it is possible. If the engine is turned over with water in the cylinders all sorts of very nasty things are likely to happen the most obvious being damage to the head gasket. If you do have water in your oil it is either fresh water from the cooling system or seawater which has siphoned in – in both cases the water and oil will have mixed via the head gasket. Have you checked for signs of oil in your coolant system?

    #75916
    Richard Proud
    Participant

    Thank you very much for the explanation. I think I understand the problem now and I have organised an analysis of the sump oil to see if it contains seawater.
    Thanks again all your replies are appreciated.

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