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Thread: 400 watt engine compartment heater

  1. #36
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    Default Re: 400 watt engine compartment heater

    I’m beginning to think that is right Gib. I’m going to the boat today to look and ponder that configuration. (Taking the thermostat in and out is not practical as we use the boat often in winter.)

  2. #37
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    Default Re: 400 watt engine compartment heater

    Quote Originally Posted by ron ll View Post
    Back to the coolant loop, here is what my water heater tank looks like. The center loop is the shore power 120v heating element, and the other three longer loops are the engine coolant which heat water underway. So while on shore power it seems like this could heat the engine if it circulated. So does it not circulate naturally because the engine coolant inlet and outlet both have equal pressure when heated so convection won’t “rise”? Or is it not circulating because the engine thermostat blocks it? If the former, maybe simply adding a circulation pump will work.

    Attachment 25580

    Questions...

    1. Is the water heater lower than the engine coolant inlet? I assume you know this already, but the heated coolant has to be able to travel up and the cold coolant has to travel down to create the thermosiphon. There are some rules about the difference in height as well but I don't know all the details.

    2. From where is the engine coolant being routed to the water heater? If the engine coolant is coming from the manifold or some other point in the actual engine coolant circuit then the thermostat won't matter. The thermostat just blocks off the coolant circuit from the heat exchanger so it can heat up faster when the engine is cold. It doesn't prevent it from circulating within the engine itself. On Skookum Maru the coolant comes from the exhaust manifold for example. You can see it at the back of the manifold in this photo:



    That point gets coolant circulation regardless of the thermostat. But I'm not sure if that setup would work to create a siphon because the inlet and outlet are at the same height? Might need to take the return lower down but again I'm not really sure on that point.

  3. #38
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    Default Re: 400 watt engine compartment heater

    Just talked to a couple of pro engine guys who convinced me the coolant pump is a bad idea. First, and I think Michael already adressed this in his schematic, one cannot just put a pump inline as it then becomes a block to normal circulation when the engine is running. So it would need a bypass setup. But they said although it can be made to work, it is adding complication to a system that if fails, has serious consequences to cooling the engine. So bottom line, it’s just not worth it in this mild climate. So I guess I’m back to the block heater replacement.

  4. #39
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    Default Re: 400 watt engine compartment heater

    Chris, yes the problem with the thermosiphon in my case is the heights are not right. Is Skookum Maru keel cooled?

  5. #40
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    Default Re: 400 watt engine compartment heater

    Quote Originally Posted by ron ll View Post
    Chris, yes the problem with the thermosiphon in my case is the heights are not right. Is Skookum Maru keel cooled?
    Interestingly, Skookum Maru has heat exchanger cooling with a dry stack. The black hose coming from the heat exchanger in the photo above is the cooling water outlet to the discharge through hull. So you get all the inconvenience of the dry stack with all of the complexity of a raw water system and none of the benefits of keel cooling. I don't know why they set it up that way originally - seems strange to me. It would be nice to replace the heat exchanger with a keel cooler at some point and remove the raw water system. Not a priority though, given that it's worked fine for the last sixty years.

  6. #41
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    Default Re: 400 watt engine compartment heater

    Quote Originally Posted by ron ll View Post
    Just talked to a couple of pro engine guys who convinced me the coolant pump is a bad idea. First, and I think Michael already adressed this in his schematic, one cannot just put a pump inline as it then becomes a block to normal circulation when the engine is running. So it would need a bypass setup. But they said although it can be made to work, it is adding complication to a system that if fails, has serious consequences to cooling the engine. So bottom line, itís just not worth it in this mild climate. So I guess Iím back to the block heater replacement.
    I don't see where this would be the case. The pump would be part of a "branch circuit" that does not interfere with the main cooling system.

    Am I mistaken?

    If so is there any reason you cannot just put a thermostatically controlled 250W baseboard heater in the engine compartment, assuming that it unplugs when not in use, or perhaps an independent hot water heating element that gets it's heat from the existing water heater?

  7. #42
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    Default Re: 400 watt engine compartment heater

    More connections to leak. New 3 way valves to remember to switch over to bypass - and off bypass when starting the engine.

    Are there any hoses where an inline heater could be plumbed? Or has this idea been rejected already?

    Marine-grade baseboard heaters might be hard to find.

  8. #43
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    Default Re: 400 watt engine compartment heater

    Thanks Gib. Probably all true, however at this point the simplest may be to just wrestle (or hire a wrestler) with replacing the existing block heater. It really does what I want it to do, just wish it were in an easier place to get at.

  9. #44
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    Default Re: 400 watt engine compartment heater

    Quote Originally Posted by ron ll View Post
    It’s behind the intake manifold, the oil filler, the dipstick housing, and generally behind everything on that side of the engine.


    It looks like there are two access ports, one on each end of the block (which makes sense since the block is symmetrical). Assuming that the one used for the block heater is the one behind the governor and not the one behind the blower drive shaft it looks like you should be able to get to it by removing the intake silencer housing and the governor. See above (ok, yes, there are a few other parts missing on that motor, but the governor is the bit that sits right over the water jacket port). Not quite a minor project but not really a huge one either I think? Maybe a couple of hours total. Could be easier than fighting to get to the block heater behind all of those parts.

  10. #45
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    Default Re: 400 watt engine compartment heater

    Thanks Chris. But if my engine looked like that it would be easy. Mine has a few more parts in the way.

  11. #46
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    Default Re: 400 watt engine compartment heater

    Quote Originally Posted by ron ll View Post
    Thanks Chris. But if my engine looked like that it would be easy. Mine has a few more parts in the way.
    Yeah, not going to be easy I guess. I’d be tempted to call Hatton and have them do it. Only so much time I want to spend fighting with recalcitrant machines...

  12. #47
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    Default Re: 400 watt engine compartment heater

    An unasked-for 2 cents...

    Dipstick heaters can, over time, do damage to oil. They also get caked up with a burnt coating, reducing their effectiveness. By far the most efficient way of heating an engine is with a freeze-plug heater as you've had. Yep, a PITA to get at - but they 1) do no damage & 2) heat efficiently.

    I don't see why it needs to be on all the time though. On diesels I've owned, I'd run a block heater for 2 hours before starting - unless more than 20 below - then I'd leave 'em on all night. While not a Jimmy guy, I'd think even those old monsters would only need 2-3 hours before startup - especially in your climate.

    With "only on for a few hours each day during the winter" usage, they'll easily last 5+ years.
    "If it ain't broke, you're not trying." - Red Green

  13. #48
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    Default Re: 400 watt engine compartment heater

    Good advice Garret but in my case I like it on all the time to add a little constant drying to the boat. As for starting, I can’t imagine getting to the boat two hours in advance of wanting to start it.

  14. #49
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    Default Re: 400 watt engine compartment heater

    Quote Originally Posted by cstevens View Post
    Yeah, not going to be easy I guess. I’d be tempted to call Hatton and have them do it. Only so much time I want to spend fighting with recalcitrant machines...
    How big is Dash? Can he swing a wrench? Does he have claustrophobia?

  15. #50
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    Default Re: 400 watt engine compartment heater

    Well here he is starting Skookum Maru a few weeks ago. He loves being in engine rooms and playing with machinery but I think his hand strength isn't quite up to the task of taking parts off yet. Give him a few years though. If my childhood is anything to go by I'll come down to the boat one day to find the motor in pieces and Dash happily sitting in the middle of all the parts.



  16. #51
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    Default Re: 400 watt engine compartment heater

    Quote Originally Posted by ron ll View Post
    I bought the heater shown in the OP, but I think Iíll return it before installing it. Itís a nice unit for its intended purpose, which is preventing engine freezing, but not really suitable for what I need. It has a thermostat which only turns the heater on at 41 F and below (the temp inside a refrigerator). Itís not very often my boatís temp gets that low so it would hardly ever turn on. My old block heater would run constantly all fall, winter and spring, making the engine easier to start and keeping the boat just slightly warmer than outside all the time, thereby helping evacuate moisture. This heater wonít do that. Bummer.
    It sounds like an awful lot of work if all you need is a small space heater that comes on at a higher temperature. explosion-proof 400/800W Kinda ugly though.
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

  17. #52
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    Default Re: 400 watt engine compartment heater

    Quote Originally Posted by ron ll View Post
    It’s behind the intake manifold, the oil filler, the dipstick housing, and generally behind everything on that side of the engine.
    On my 6-71 there's two - one where you describe, behind the blower, easy to see but looks like you'd have to disassemble half the engine to change it.

    But the other one is just screwed into a tapped hole up by the header tank. I've got the long header tank that gaskets directly to the top of the exhaust manifold, and one of those larger pipe-thread holes up near where they join has a heater screwed into it.

    Can't say how good that works, I haven't gone through a winter with her yet but it sure is easy to get to. And it goes into the coolant system so I see no reason to think it won't work.

    btw, not sure about this concern over preheating a Detroit. At least this one starts before it even makes one revolution on the starter. They do start good. But as a safe means to keep the boat warmish and dry over the winter, good idea ! Use the engine as a heat sink ...
    Last edited by Favorite; 11-02-2018 at 02:05 PM.

  18. #53
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    Default Re: 400 watt engine compartment heater

    Do you mean one of these? Are they into water jackets? I thought those were into the exhaust manifold. Or do you mean the one on top of the tank?

    Actually, now that I look at it, the one I have marked as "B" is where my keel cooler connects so I guess that is a water jacket.

    0A5DE559-76F5-4DCD-A49B-AD987871C05C.jpg
    Last edited by ron ll; 11-02-2018 at 03:27 PM.

  19. #54
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    Default Re: 400 watt engine compartment heater

    Quote Originally Posted by ron ll View Post
    Do you mean one of these? Are they into water jackets? I thought those were into the exhaust manifold. Or do you mean the one on top of the tank?
    A little forward of your "A" point on the vertical face is where my second heater is located. There's a couple of threaded holes there. Detroits come in so many different configurations that it's hard to say, but mine looks similar to yours.

    I agree the lower position should work better in theory, but sometimes we get carried away with theory

    I'd take a picture but it probably wouldn't show anything ... pretty hard to get a good angle on it for a camera. Yes, that manifold above the exhaust ports is for coolant and it connects directly into the header tank.

    For that matter, you might be able to stick a 500w aquarium heater through the radiator cap and that would work, too. They make stainless steel unbreakable aquarium heaters ...

  20. #55
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    Default Re: 400 watt engine compartment heater

    I’ll certainly take a second look at my engine. It would be great to get an accessible port in that area. Thanks for your help.

  21. #56
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    Default Re: 400 watt engine compartment heater

    Quote Originally Posted by ron ll View Post
    I’ll certainly take a second look at my engine. It would be great to get an accessible port in that area.
    Sorry about the photo. In my defense, flashlight in one hand, phone in the other, contorted into a pretzel, pushed the button with my nose.

    Looking forward, the top asparagus-green thing is the header tank where it comes around the corner. The mid-level green thing is the manifold that bolts on across the top of the exhaust ports. On the left with the teflon tape showing is the heater. That corrugated plastic thingy covers the wires.

    blockheat.jpg

    Thanks for your help.
    No prolemo senor. Us detroiters gotta stick together. We're a dying breed

  22. #57
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    Default Re: 400 watt engine compartment heater

    I think I get where that is, I am also starting to understand why I haven’t seen it, it would be pretty hidden on my engine given the floorboard configuration and lack of viewing angles. But it would be fairly easy to access if it is there, at least far easier than the lower one. Hopefully I can get to the boat today to check it out. Gracious again.

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