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  1. #1
    Join Date
    Jul 2019
    Posts
    5

    Default Isotemp unit drained for winter, shut off engine coolant feed ?

    Hi all
    Iím going to drain my isotemp water unit for winter, but will still go out a few more times before it gets cold. Do I need to shut off the engine coolant circuit going into the water unit or is it ok to leave coolant flowing through heating the elements ?
    Many thanks

  2. #2
    Join Date
    May 2001
    Location
    Jersey/Antibes
    Posts
    22,681

    Default Re: Isotemp unit drained for winter, shut off engine coolant feed ?

    It totally doesnít matter either way. Just take the opportunity to exercise the valves. I would leave them open so the heating coil gets flushed with use, but really it just doesnít matter.
    Remember to turn off the electric element at the breaker and tape it in the off position!

  3. #3
    Join Date
    Mar 2002
    Posts
    17,746

    Default Re: Isotemp unit drained for winter, shut off engine coolant feed ?

    I'd shut the engine coolant circuit off, and never open it again.
    That's what I did also in my boat right after buying her, because in my experience most of nautical boiler failures are one way or another related to that.
    Circulating water at 80+ degrees inside a boiler doesn't make any sense, and unless you use your boat with neither dock nor genset AC supply for longish periods, the electrical heating (which I set around 50deg) is more than enough to guarantee an adequate supply of hot water.

  4. #4
    Join Date
    May 2009
    Location
    cambridge/Isle of Wight
    Posts
    613

    Default Re: Isotemp unit drained for winter, shut off engine coolant feed ?

    Quote Originally Posted by MapisM View Post
    I'd shut the engine coolant circuit off, and never open it again.
    That's what I did also in my boat right after buying her, because in my experience most of nautical boiler failures are one way or another related to that.
    Circulating water at 80+ degrees inside a boiler doesn't make any sense, and unless you use your boat with neither dock nor genset AC supply for longish periods, the electrical heating (which I set around 50deg) is more than enough to guarantee an adequate supply of hot water.
    Not sure I understand your logic in isolating permantly , would have thought it double ups as a heat sink for one of the engines, plus the benefit of hot water , also 50 deg water temp can allow legionnaires bacteria to survive but not multi ply

  5. #5
    Join Date
    Jul 2019
    Posts
    5

    Default Re: Isotemp unit drained for winter, shut off engine coolant feed ?

    Thanks all, at this stage I’ll drain the system & disconnect the electric heater while trying to enjoy the last blast of the season! . MapisM I rarely use shore power as we haven’t owned her long and she doesn’t have a galvanic isolator fitted (next job!).

  6. #6
    Join Date
    Mar 2002
    Posts
    17,746

    Default Re: Isotemp unit drained for winter, shut off engine coolant feed ?

    Quote Originally Posted by dj43 View Post
    Not sure I understand your logic in isolating permantly , would have thought it double ups as a heat sink for one of the engines, plus the benefit of hot water , also 50 deg water temp can allow legionnaires bacteria to survive but not multi ply
    Well, you can set also the electric heating higher than 50 deg, if you wish.
    But I don't think you keep your home boiler at 80+ deg anyway, do you?

    Regardless, the double use as heat sink for one engine is precisely where these nautical boilers are intrinsically flawed.

    Lets forget the possible benefit of having hot water 24/7 during passages measured in days (if not weeks) rather than hours, because that's a totally unrealistic scenario for the overwhelming majority of moboers.
    And for us mere mortals, it's sufficient one night at anchor to lose the benefit of arriving in a spot with the water already warm, and after running out of hot water, you'd rather turn on the genset than the main, obviously.

    Anyway, from the engine viewpoint, it doesn't make sense to cool it a bit more or a bit less depending on the hot water usage onboard, and regardless of whether it's already warmed up or not.
    Not that I think the short path where cooling liquid goes through the boiler makes a meaningful difference, mind.
    But as an engine heat sink, it's pointless by design, so to speak.
    Last edited by MapisM; 13-10-19 at 21:07.

  7. #7
    Join Date
    Mar 2002
    Posts
    17,746

    Default Re: Isotemp unit drained for winter, shut off engine coolant feed ?

    Quote Originally Posted by Meagain View Post
    MapisM I rarely use shore power as we haven’t owned her long and she doesn’t have a galvanic isolator fitted (next job!).
    All well and good, but do you keep moving each and every day?
    As I previously said, while anchored I would turn the genset on (hence the electrical heater) rather than the engine...

  8. #8
    Join Date
    Dec 2001
    Location
    north ayrshire
    Posts
    492

    Default Re: Isotemp unit drained for winter, shut off engine coolant feed ?

    Im not getting the turn off the engine water heating permanently either. Here on the west coast of Scotland we regularly hop from one anchorage to another on a daily basis, maybe dropping into a marina every 3 or 4 days or so to replenish water tanks, replenish supplies, dump rubbish & for everyone to take a shower. The water heated from the engine is usually enough for everyone to get washed & dishes washed & the occasional shower, usually taken whilst on the move at displacement speed which means we still have hot water for general use when we arrive.

  9. #9
    Join Date
    Mar 2002
    Posts
    17,746

    Default Re: Isotemp unit drained for winter, shut off engine coolant feed ?

    Well, I still hate hot water hoses+joints all around the boat filled with very high temperature water, hence exposed to premature failures/leaks.
    But that's me, of course.

  10. #10
    Join Date
    May 2009
    Location
    cambridge/Isle of Wight
    Posts
    613

    Default Re: Isotemp unit drained for winter, shut off engine coolant feed ?

    Quote Originally Posted by MapisM View Post
    Well, you can set also the electric heating higher than 50 deg, if you wish.
    But I don't think you keep your home boiler at 80+ deg anyway, do you?

    Regardless, the double use as heat sink for one engine is precisely where these nautical boilers are intrinsically flawed.

    Lets forget the possible benefit of having hot water 24/7 during passages measured in days (if not weeks) rather than hours, because that's a totally unrealistic scenario for the overwhelming majority of moboers.
    And for us mere mortals, it's sufficient one night at anchor to lose the benefit of arriving in a spot with the water already warm, and after running out of hot water, you'd rather turn on the genset than the main, obviously.

    Anyway, from the engine viewpoint, it doesn't make sense to cool it a bit more or a bit less depending on the hot water usage onboard, and regardless of whether it's already warmed up or not.
    Not that I think the short path where cooling liquid goes through the boiler makes a meaningful difference, mind.
    But as an engine heat sink, it's pointless by design, so to speak.
    Here in the uk we do run our heating appliances at 75deg plus , to heat hot water, that is regulated around 60 deg,
    Also we don't tend to stay at anchor for any length of time , due to our wonderful weather, in my experience anyway , and are always glad of the hot water when we stop to have a shower to warm up

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