Will a Propane-powered 5 hp Mercury Propane-Powered Outboard Engine Work With Butane Fuel?

Hi. Welcome to today's Stump Question.

Can't find an answer on the web, called Mercury national Customer Service Center and they had no information or advice (pretty fucking weak, IMO)- surprisingly, the guy had no clue. Hard to believe I'm the first person to ask this question. I bought the 5 hp propane-powered outboard last year and I really like it. Am moving to Europe next year to cruise, and over there, butane, not propane, is used. The two gases are similar, but will the engine work with butane? Are any modifications or adjustments required? Thanks for any assistance, y'all!
 

El Borracho

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Is the engine specified for propane or LPG? In summer and in warm climates LPG bottles will most likely be filled with mostly butane anyways. That is why the marketing was changed to LPG from propane. Butane is cheaper.

I’d expect no difference in engine preference.
 
Is the engine specified for propane or LPG? In summer and in warm climates LPG bottles will most likely be filled with mostly butane anyways. That is why the marketing was changed to LPG from propane. Butane is cheaper.

I’d expect no difference in engine preference.
Thanks for the guess. The engine is specified for propane.

 

Monkey

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Hi. Welcome to today's Stump Question.
Can't find an answer on the web, called Mercury national Customer Service Center and they had no information or advice (pretty fucking weak, IMO)- surprisingly, the guy had no clue. Hard to believe I'm the first person to ask this question. I bought the 5 hp propane-powered outboard last year and I really like it. Am moving to Europe next year to cruise, and over there, butane, not propane, is used. The two gases are similar, but will the engine work with butane? Are any modifications or adjustments required? Thanks for any assistance, y'all!
In defense of the customer service center not having an answer, they can only respond with the information they have. Just for fun, try reaching out to Nissan and Tohatsu. It’s the same engine, so maybe they’ve experimented with butane.

Edit: I did check our engineering database and couldn’t find any references to testing with butane.
 

TJSoCal

Super Anarchist
My googling tells me that butane and propane have significantly different densities and vapor pressures. So I suspect you'd need to change regulator and jets to make a motor designed for propane work properly with butane.
 

Monkey

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My googling tells me that butane and propane have significantly different densities and vapor pressures. So I suspect you'd need to change regulator and jets to make a motor designed for propane work properly with butane.
The link I attached a few posts ago said Tohatsu’s engineers said it’ll run on propane and LPG, but that’s just an article found on the internet. I sent an email to one of the engineers from them I’ve worked with on that engine. He’ll know the right guy in their company to give a definitive answer. I specifically asked about butane.

Edit: and assuming it will run on butane, I’ll even get the Tohatsu part numbers of the parts Rude Dog will need to buy to swap. I’m guessing it’ll just be the gas fittings. For the record, I’m not speaking on behalf of my company, but happy to abuse company connections to help another sailor.
 
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El Borracho

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Thanks for the guess. The engine is specified for propane.

If butane is ruled out then their market is ruined. Likely difficult to buy propane in any area or season with above freezing temperatures. Astonishing that a useful specification is not available. LPG (aka propane in trailer parks) is a mixture of a half dozen similar gasses. Even europe’s “butane” might be just another archaic name for LPG.

Proper butane will not come out of the bottle in freezing weather as any backpacker knows.
 

Monkey

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If butane is ruled out then their market is ruined. Likely difficult to buy propane in any area or season with above freezing temperatures. Astonishing that a useful specification is not available. LPG (aka propane in trailer parks) is a mixture of a half dozen similar gasses. Even europe’s “butane” might be just another archaic name for LPG.

Proper butane will not come out of the bottle in freezing weather as any backpacker knows.
I can’t answer specifically, but have a pretty good hunch why Merc didn’t have an answer. First off, it was designed and built by Tohatsu with Merc and Nissan funding. Second, a lot of the joint ventures come with marketing agreements. Why would we test for a fuel outside our market? That’s my best guess as to why customer service didn’t have an answer.

Edit: If you want to properly go fast in your dinghy, I can help you out in anything from our 650 to 75. Anything less than that is built over seas.
 
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kent_island_sailor

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What I am getting out of this is "propane" is actually some mixture of flammable gasses that changes with the seasons and the vendors, so probably tons of these engines have been run on butane already without anyone realizing it.
OTOH - Our home propane tank lasts about a year, so if it got filled with butane in the summer the stove would quit working on cold January nights and it doesn't.
 
Hi. Welcome to today's Stump Question.

In defense of the customer service center not having an answer, they can only respond with the information they have. Just for fun, try reaching out to Nissan and Tohatsu. It’s the same engine, so maybe they’ve experimented with butane.

Edit: I did check our engineering database and couldn’t find any references to testing with butane.
Thank you for the tip and comments.
 
The link I attached a few posts ago said Tohatsu’s engineers said it’ll run on propane and LPG, but that’s just an article found on the internet. I sent an email to one of the engineers from them I’ve worked with on that engine. He’ll know the right guy in their company to give a definitive answer. I specifically asked about butane.

Edit: and assuming it will run on butane, I’ll even get the Tohatsu part numbers of the parts Rude Dog will need to buy to swap. I’m guessing it’ll just be the gas fittings. For the record, I’m not speaking on behalf of my company, but happy to abuse company connections to help another sailor.
Many, many thanks- very cool of you.
 

Monkey

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Many, many thanks- very cool of you.
So the deal is that it will run on butane, but with a few caveats.

It’s almost useless in cold weather. Performance drops about one horsepower. It will also be harder to start.

Basically, it’ll work but you might not like it.
 

Monkey

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More info arrived. It’s optimized for at least 60% propane in the LPG. The engine sells as well in Europe as any other market, so their “butane” may just be wonky labeling. I have no clue on that, but I can’t imagine people buy engines they can’t fuel.

Oh, and there are no conversion parts between their’s and your’s. The ones sold in Europe have the same connection as your Merc. Aftermarket adapters are the only option, if needed.

Edit: And I loaded all that info in to our database, so the next guy who calls customer support will get a better answer. ;)
 
More info arrived. It’s optimized for at least 60% propane in the LPG. The engine sells as well in Europe as any other market, so their “butane” may just be wonky labeling. I have no clue on that, but I can’t imagine people buy engines they can’t fuel.

Oh, and there are no conversion parts between their’s and your’s. The ones sold in Europe have the same connection as your Merc. Aftermarket adapters are the only option, if needed.

Edit: And I loaded all that info in to our database, so the next guy who calls customer support will get a better answer. ;)
Amazing info- I am so appreciative!

And a small performance drop-off is not an issue. You see, my RIB is only 8' and with a soft bottom and incapable of high speeds, so even a 5 hp motor is overkill- you can't even get to half throttle without overpowering the craft, so I oughta be OK. Here's my RIB- I've modified the the engine cover and propane tank colors to a more subtle flat Navy grey paint, from rapcoparts.com.
1661613192082.png
 




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