Replumbing an Outboard for Heat

Discussion in 'Outboards' started by DogCavalry, Nov 24, 2021 at 5:37 PM.

  1. DogCavalry
    Joined: Sep 2019
    Posts: 1,754
    Likes: 907, Points: 113
    Location: Vancouver bc

    DogCavalry I aim to misbehave.

    I'm sure this question has come up before. But the search terms in the forum are unhelpful some times. What is the path of heated water from the engine back to the sea from an outboard, like a 150, or sonething bigger? Understanding that, could a competent technician drill a port into the leg with a diverter, to bring that heated water into the cabin, then if needed, back to the leg and out? Or possibly 2 diverter penetrations that close the system, or partially close the system, for typical Canadian January days? I can imagine days cold enough where all the heat rejected from the engine still wouldn't make the cabin very warm.
     
  2. ondarvr
    Joined: Dec 2005
    Posts: 2,709
    Likes: 426, Points: 83, Legacy Rep: 506
    Location: Monroe WA

    ondarvr Senior Member

    This is a common modification for small outboards used for trolling in the PNW. Not as often on larger outboards for no other reason than when it's running you aren't typically using the warm water.

    Not every outboard has the water flowing in the same direction or route, so you need to track it yourself, or refer to the manual.

    You drill and tap a hole into the head in a location that allows the water to have picked up enough heat to be useful, sometimes that can be the thermostat cover, or it may be in the water jacket on the head.

    You can return the water overboard, which is more common, or find a lower pressure location to return it to the block. You can try to return it to the midsection, but sometimes it isn't as convenient.

    This is normally used to heat water that is used to wash your hands while fishing. It flows into a small tank that holds a gallon or so of water and then out an overflow hole over the side.

    It makes a great hand warmer for those very cold days.

    With larger tubing and a heat exchanger you could at least get some heat off an outboard, maybe not enough to make it worth the effort though.
     
    DogCavalry likes this.
  3. DogCavalry
    Joined: Sep 2019
    Posts: 1,754
    Likes: 907, Points: 113
    Location: Vancouver bc

    DogCavalry I aim to misbehave.

    Thanks @ondarvr ! Exactly as I suspected, but asking someone who knows>a good guess.

    I think with 100% of the cooling water diverted to a radiator inside, a 150 should give enough to help. Certainly that's more power than the engine in my astro is typically delivering, cruising on the highway. Although the cabin of a boat large enough to live in would be a lot of space to heat.

    I take your point about the tapping point being particular to an individual group of engines. And all the water may not be available. Certainly some is needed to cool the exhaust. But given the thermal efficiency of an ICE, getting that heat back would be great. Particularly during Canadian winter on the Pacific.
     
  4. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,388
    Likes: 1,021, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    You need to be a bit careful I think, most of water goes down the exhaust route, and if you hijack too much of it, could end up with hot exhaust causing problems in the lower parts.
     
    fallguy likes this.
  5. trip the light fandango
    Joined: Apr 2018
    Posts: 472
    Likes: 94, Points: 28
    Location: Rhyll Phillip Island Victoria Australia

    trip the light fandango Senior Member

    Drawing warm air from the cowling could help, might want a carbon monoxide sensor just in case, or a double skin. Also using exhaust water to heat the seats could radiate well and get the heat somewhere useful. A close up thermometer of how the motor is going,ha.
     
    DogCavalry likes this.
  6. jehardiman
    Joined: Aug 2004
    Posts: 3,065
    Likes: 569, Points: 113, Legacy Rep: 2040
    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    Yep, the cooling water is used to cool the exhaust gasses, in most hub outlet outboards. Otherwise the lower unit will over heat.
     
    DogCavalry likes this.
  7. Barry
    Joined: Mar 2002
    Posts: 1,490
    Likes: 280, Points: 83, Legacy Rep: 158

    Barry Senior Member

    I am sure that you have looked at the Wallas combination stove/heater, but check with a couple of owners as someone told me that they take quite a bit of time to boil water/cook etc. Then you have heat any time you need it.
    We had a small Force 10 back in the 80's in a 26 foot cabin cruiser though it was a low on output. Dickenson makes a diesel cabin heater and probably others.
     
  8. BlueBell
    Joined: May 2017
    Posts: 1,781
    Likes: 501, Points: 113
    Location: Victoria BC Canada

    BlueBell "Whatever..."

    What make, model and year is your engine John?
    Have you Googled around for a shop manual ( the original that is ) ?
    Perhaps someone here on the Forum has direct experience with your engine make, model and year.
    How would you plumb the hot water delivery to where it's needed?
     
  9. DogCavalry
    Joined: Sep 2019
    Posts: 1,754
    Likes: 907, Points: 113
    Location: Vancouver bc

    DogCavalry I aim to misbehave.

    The engine I'm messing with right now is a 94 Johnson 150. Maybe a runner, maybe not.
     
    Last edited: Nov 25, 2021 at 9:24 PM
  10. DogCavalry
    Joined: Sep 2019
    Posts: 1,754
    Likes: 907, Points: 113
    Location: Vancouver bc

    DogCavalry I aim to misbehave.

    The particular path the water takes is the most important aspect. Is the water coming in cold cooling the exhaust before it goes into the block? I imagine that would reduce thermal shock. Or if it ends its journey at the exhaust that's an entirely different matter.
    Another concern is length of run. Can't expect the impellor to do more than originally designed for. I envision very short runs of large diameter rad hose dumping into the top of a heat exchanger, that pours out of an even larger hose that takes water off the bottom ( to allow stratification at a thermocline). A closed system carries the working fluid- maybe potable water, maybe just air- forward into the cabin. The heat exchanger would probably be located at the transom, in the middle under the aft deck sole.

    @Barry I may well use those units. I'll need something, that much is clear. The heat failed in my work truck, and I went a few weeks wiping all the windows down every 2-3 minutes, just to see to drive. Very tiring, and not safe.
     
  11. Barry
    Joined: Mar 2002
    Posts: 1,490
    Likes: 280, Points: 83, Legacy Rep: 158

    Barry Senior Member

    Just thinking that perhaps an ex Johnson/Evinrude/BRP dealer may have an almost scrapped engine in their boneyard that you could pick up for a case of beer/wine/etc and you could just take it apart to find the passages
     
    DogCavalry likes this.
  12. DogCavalry
    Joined: Sep 2019
    Posts: 1,754
    Likes: 907, Points: 113
    Location: Vancouver bc

    DogCavalry I aim to misbehave.

    Heck of a good idea, @Barry .
    I have a good enough understanding of engines and thermodynamics that I'm sure I can do it without wrecking thf engine. IF I know exactly how it's plumbed inside.
     
  13. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,388
    Likes: 1,021, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    water has to reach the top of the powerhead to flow back out, this idea is fraught in my opinion, in cold conditions and cold water the flow is interrupted by the thermostats, and the more you endeavour to "steal" warm engine water, the more they will close. The thermostats are there to keep the engine operating in the ideal temperature range, too low is harmful and causes rapid wear and tear.
     
  14. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,388
    Likes: 1,021, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    I wouldn't even consider it, you may create unexpected problems in an old engine that I'd be very happy if it just kept going, especially pushing around that behemoth. But of course here in sunny Queensland we are pre-occupied with keeping cool, not defrosting !
     

  15. DogCavalry
    Joined: Sep 2019
    Posts: 1,754
    Likes: 907, Points: 113
    Location: Vancouver bc

    DogCavalry I aim to misbehave.

    I'm not stealing anything. An internal combustion engine needs to reject heat to the environment. I hope to run that hot water through a heat exchanger, like any vehicle (around here anyway) does, so that it's not wasted.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.