Propane Outboard?

Discussion in 'Outboards' started by Wavewacker, Jul 9, 2012.

  1. Wavewacker
    Joined: Aug 2010
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    Wavewacker Senior Member

    What would be the pros and cons of having a small OB (5 to 20 hp) converted to propane or natural gas?

    Seems you haul proapane for the stove/oven, why haul both? I wouldn't want a gas fired stove and heater.

    Could they be converted to run on either gas and/or natural gas/propane?

    Seems tanks would be lighter too!

    What say you?
     
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  2. keysdisease
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    keysdisease Senior Member

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  3. fredsnotdead
    Joined: Jul 2012
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    Location: illinois

    fredsnotdead Junior Member

    Thanks for the heads up for that. I just wish they had it in a remote steer configuration, and maybe it could be switched with little work. I don't think that I would venture too far with just a 1 lb tank though.
     
  4. Wavewacker
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    Wavewacker Senior Member

    Well, the defender has an aux tank set up, I was thinking more like a much larger tank.

    Okay, they are green, that's nice, but what about fuel economy, power at the tap?

    What about larger engines, like a 20 or 25......even 50 hp? I know vehicles are converted, can you convert any OB?
     
  5. fredsnotdead
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    fredsnotdead Junior Member

    Way back when(1970's and 80's), all the trucks, school buses, and farm tractors ran on propane, with the truck and bus engines being dual fuel with gas also. I had a dually p/u with two tanks and propane too, and I liked the propnae for pulling a trailer and the three tanks combined gave me a really long range.
    Here in the cornbelt with all the Ethanol plants located here, getting outboards, lawnmowers, chainsaws, and weedwhackers to run on the blended crap is a real nightmare. In the last few years, every Spring you see about 10-15 weedwhackers out for trash because of that blended junk. And, when you go to any river or lake you hear the noise of motors turning over but not starting for the same reason. the bigger F/I outboards start and run a lot better and it seems over 150 or 100 specifically seems to be the threshold.
    I've never actually done a conversion but have friends that have converted quite a range of small 4 stroke motors for various things just because of the fuel problems. The blends mixes vary a lot, but it's not as bad as last year and I think it's because of the loss of the Veetc(blenders tax credit). There's now way in hell that you could have pull-start outboard around here and not have already thrown it overboard. I want to run an electric o/b on a pontoon just for this reason, and because we don't travel very far at all(1-2 miles total). This would be nice and I think would have excellent power and torque because of the higher octane of propane.
     
  6. Wavewacker
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    Wavewacker Senior Member

    So, it can be done...I'd want an alectric start, no cord yanking for me!

    Are these conversions in a kit?

    Electric would be great, but impratical for me as I'd want to run for hours, maybe all day....Thanks
     
  7. Petros
    Joined: Oct 2007
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    Petros Senior Member

    converting both large and small engines to run on propane is done all the time. I bought a kit to covert our gasoline generator to propane, we live on rural property and out power goes out every winter (and some summers too!). The shitty federal methnol blend gasoline we are forced to buy ruins the tiny carb on the generator, I had to rebuild it every year (ususlly in the dark using a flashlight!). We also have a 500 gallon tank of propane on our property to heat the house, so I figured a conversion to propane was the way to go (we also get the propane delievered to our house for only $1.80 a gallon, now I am considering converting our cars to run on propane too!).

    Propane has a little less energy per gallon than gasoline, so you will have carry more to get the same range, it runs clean, puts out less co2, and will not gum up or corrode the carb or other parts of the engine. And it costs less. It also has 115 octane rating, if you really want to take advantage of that, and gain back some of the lost power, you could build an engine with 12 or 13 to one compression ratio. but you could not run regular gasoline in it, you would need aviation gas, or a racing fuel blend.
     
  8. Wavewacker
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    Wavewacker Senior Member

    Petros, with 115 octane I thought you'd get more power from an engine than the 87 regular....:confused:

    Is there anyway to estimate the propane required for a 26' sharpie to have a 100 mile range with a 10-20 hp calm water? I just wonder how much more you have to haul than gas, speed is not an issue really....
     
  9. CDK
    Joined: Aug 2007
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    CDK retired engineer

    The fuel consumption, measured by weight, is approx the same as with gasoline. Because propane is lighter than gasoline, the volume is 20% larger.
    The octane number has no influence on the power you get from a gasoline engine, only if the engine is modified (higher compression) more output is possible.
     
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  10. broke_not
    Joined: Jun 2008
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    Location: North Dakota

    broke_not Junior Member

    It is done all the time, but I wouldn't do it without the okay from the engine manufacturer themselves.

    On another forum I frequent, a member mentioned wanting to convert his WG750 Kubota engine, (3 cylinder water-cooled, ~22 hp), to run on propane. I told him that we have several such Kubotas in the fleet that are factory dual-fuel engines and are identified as DF models instead of WG models. Every single one of them has a decal on the rocker cover that indicates they were designed to run on either gasoline or propane. We also have several WG750s that are gasoline-only and have no such decal.

    The other guy posted a link to an aftermarket website that sells the conversion kits FOR the WG750 engines and therefore "proved" there was no difference in the engine itself. I knew otherwise, but I emailed Kubota anyway and asked them. They sent me a reply indicating that the dual-fuel engine did in fact have a differences in the head and valves. I posted a copy of their email on the forum, and the guy wanting to convert his engine was STILL having none of it.

    Here's what the Kubota rep sent me:

    The other forum member chose to rely on the testimony of the aftermarket kit conversion company....instead of the actual engine manufacturer that went to the trouble of producing two different engine variations.

    Not saying you'll *automatically* suffer dire consequences if you do such a conversion, but check with the manufacturer of the engine before doing so. All it takes is an email or phone call. Kit manufacturers that come up with some plumbing bits and pieces and a bracket or two for sale as a "kit" have NOT necessarily done their homework.

    It also doesn't matter one bit if THEY tell you modifications they recommend and sell kits to perform won't violate a manufacturer's warranty.
     
  11. mike reese
    Joined: Jul 2012
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    mike reese automotive tech

    :)

    sir i enjoyed reading your info.i am an automotive repair shop owner as well as a mechanic
    i have not worked on any propane vehicles but i do have a propane enrichment kit for
    diagnostic purposes.i believe you had mentioned about another site or forum about propane conversions if so could you let me know the site. again enjoyed your comments can tell you are sharp thanks
     
  12. CDK
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    CDK retired engineer

    Broke_not, I don't think the Kubota people are telling you the truth because they have a commercial interest that tends to prevail.
    In the early days of propane conversion there was a problem with Ford engines, where valve seats sometimes came loose. As you probably know these are pressed in the head, just like in engines of all other brands, but Ford allowed more tolerance than GM, VW, Mercedes, Renault etc.
    Instead of admitting their production process was sloppier than their competition they offered a "special LPG head", so they turn their mistake into a profitable operation.
    Nowadays quality control has greatly improved and you can convert any automotive engine without troubles.

    It may be that Kubota in 2012 still builds engines with valve seats that may come loose with the higher combustion temperatures of propane and they make an extra buck hiding that.

    I have personally converted several engines, among them a GM 5.7 V8, two straight 6 engines in AMC Pacers, a Mercruiser 3.0, a Volvo Penta 120 HP and some small generators. The only issue I encountered with boat engines was the drop in cooling water temperature caused by the evaporation of propane. Unless you let the engine idle until a decent operating temperature is reached, the water freezes in the pressure regulator causing the flow of propane to stop. In cars with a proper anti freeze mixture the problem does not exist.

    Mike Reese, I'm sorry, but I can't recall I mentioned another forum or site.
     
  13. broke_not
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    broke_not Junior Member

    Why would they still produce DF and WG versions of the same engine? Why would they offer up advice themselves as to how to properly swap out the head components? If they aren't "telling the truth", why wouldn't they offer up a simple kit consisting of the same bits the kit manufacturers do?

    The rocker cover decal on the DF engines illustrates the engine's fuel compatibility. The WG engine, (the exact same engine as the DF except for the seat/valve differences), has no such decal.

    How do they make an extra buck by producing two variations? Commonality saves money in production situations. Making two variations of the same engine and providing parts and support wouldn't save them any money at all.

    To top it off, like I said the aftermarket kit manufacturers have a simple kit for the WGs. The aftermarket kit manufacturers say there isn't anything different about the engines. Browsing a Kubota parts manual reveals that there are differences in the two. So who's "not telling the truth in order to make an extra buck"?

    Like I said, the end-user probably won't suffer any dire consequences if they do a backyard conversion. Kubota is likely assuming the owner will put on thousands of hours and they want that owner to have reliable and trouble-free service over the course of the engine's lifetime.

    The kit manufacturer on the other hand, put some plumbing bits and pieces, some short sections of hose, a bracket or two, and some miscellaneous hardware in a bag and passes it off as a "kit" that has of course been tested, approved, and signed off on as if any necessary homework has been done....including consulting the engine manufacturer themselves.

    It's obviously not the case. Choose any of the manufacturers that sell kits for the WG engines and send them an email....you'll see.

    So have I. And in the some of the earlier conversions I've seen, the engines experienced issues with valve and seat erosion because the engines were never intended to operated with "dry" fuel. Not all engines have always been produced with pressed-in seats either. Some seats were machined right into the head casting itself. I spent quite a few hours after school years ago running a Sioux valve/seat grinder, and it wasn't until lead in gasoline was phased out that pressed-in seats became the norm with cast iron heads...

    From Wiki:

     
  14. CDK
    Joined: Aug 2007
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    CDK retired engineer

    What price difference is there between engines with the decal and those without? Maybe that explains the two versions.
    My company (electronics) made good money by labeling the same product differently, like commercial grade, industrial and military. The market for mil spec was too small to do just that, but it was the icing on the cake.
     

  15. Frosty

    Frosty Previous Member

    What can the cost difference be of a compliant valve and seat to a non compliant.

    We are talking of a twin here thats 2 valves each,= pennies.

    But in reality we are talking reduced warranty claims, compliant kits, service intervals complicating warranty claims etc.

    ( you run it on what) ( you did what) oh no no no

    This is not a 4 valve per cylinder Ferrari.

    Fear and ignorance costs money.
     
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