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Old 18-05-2012, 11:28   #1
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Convert Gas Engine to LPG. How Difficult Would it Be?

Fuel problems from unstable gas are a pain, and I'm looking at those new Lehr engines as a good idea. However, Lehr is an unknown without a dealer parts/service network, and the engines are made in China (?). The outboards aren't out long enough to have a track record, but user reviews of Lehr garden products on Amazon.com aren't encouraging (for quality).

I'd love to see a major maker such as Yamaha/Honda/Mercury/Tohatsu/Suzuki/etc. come out with propane powered outboards.

Meanwhile, I'm thinking LPG CONVERSION! Is this difficult?
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Old 18-05-2012, 11:40   #2
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Re: Convert gas engine to LPG. How difficult would it be?

The only thing I use gasoline (petrol) for on board is the dinghy outboard. It's expensive -- I guess $2.50 a liter -- not a gallon! -- and my 25 horsepower Mariner burns through a lot of it. It's a moderate pain to buy and store.

I like the idea of a CNG conversion -- would eliminate problems with stale fuel, gummed up carbs, etc. I bet it would be cheaper to run than petrol (at least at the prices here).

Just one little problem -- lubrication. Few small outboards have oil injection.

Another problem -- where to get CNG? You wouldn't want to use LPG (propane, or butane cooking gas) -- heavier than air, and presenting all kinds of safety problems.
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Old 18-05-2012, 12:10   #3
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Re: Convert gas engine to LPG. How difficult would it be?

When I was working for a municipal police department, we had a two FORD Crown Vics delivered with Compress Natural Gas (CNG) engines as an experiment. Although in theory the idea was good (Clean available fuel), the fuel milage was terrible at about 80 miles per tank full (The fuel tank took up the entire trunk). Also the performance was signifcantly reduced, as compared with the gas engine Crown Vics.

I suspect it would be the same with LPG outboards, so depending on the application, you would have to carry a very large tank to make it worth while and your performance would be cut.

I also read a few things about LPG outboards and found numerous people have done conversions. The problem they all talk about is lack of fuel near the water, difficultly with the fuel bottles freezing over/losing pressure and finally about reduced perfomance of their outboard engines.

Based on that, if you search the internet you will find several manufactures and sellers on Ebay are selling conversion kits for outboards, as well as a cople of forum discussions on this very topic. I used LPG Outboard as search words.

IMHO... Spending several thousand dollars on an LPG conversion because of fuel quality seems a bit extreme to me... I would just purchse some fuel stabilizer and call it a day, but I am not you.

I sometimes shoot my mouth off... So don't let me deter you. I wish you good luck and if you do the conversion, I would be interested in hearing how it works out.
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Old 18-05-2012, 12:29   #4
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Re: Convert gas engine to LPG. How difficult would it be?

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Originally Posted by Dockhead View Post
The only thing I use gasoline (petrol) for on board is the dinghy outboard. It's expensive -- I guess $2.50 a liter -- not a gallon! -- and my 25 horsepower Mariner burns through a lot of it. It's a moderate pain to buy and store.

I like the idea of a CNG conversion -- would eliminate problems with stale fuel, gummed up carbs, etc. I bet it would be cheaper to run than petrol (at least at the prices here).

Just one little problem -- lubrication. Few small outboards have oil injection.

Another problem -- where to get CNG? You wouldn't want to use LPG (propane, or butane cooking gas) -- heavier than air, and presenting all kinds of safety problems.
An alternative approach is just to make your gasoline engine use a lot less fuel. What I did was forget about planing, and go for a small 4 stroke engine. A new 5hp one should use about a litre / hour.
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Old 18-05-2012, 12:58   #5
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Re: Convert gas engine to LPG. How difficult would it be?

Quote:
Originally Posted by Dockhead View Post
The only thing I use gasoline (petrol) for on board is the dinghy outboard. It's expensive -- I guess $2.50 a liter -- not a gallon! -- and my 25 horsepower Mariner burns through a lot of it. It's a moderate pain to buy and store.

I like the idea of a CNG conversion -- would eliminate problems with stale fuel, gummed up carbs, etc. I bet it would be cheaper to run than petrol (at least at the prices here).

Just one little problem -- lubrication. Few small outboards have oil injection.

Another problem -- where to get CNG? You wouldn't want to use LPG (propane, or butane cooking gas) -- heavier than air, and presenting all kinds of safety problems.
1 gallon gasoline 125,000 BTU
1 gallon propane 92,500 BTU
So need to carry 1.35 gallons of propane to match 1 gallon of gas.

1,030 BTU per cubic foot of natural gas.
So 121 cubic feet of natural gas to match 1 gallon of gasoline.
You can get 120 c.f. tanks, 3500 psi, about 40 lbs empty.
Carry one full size 40 lb scuba tank for each gallon of gasoline you would bring with you.

John
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Old 18-05-2012, 13:31   #6
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Re: Convert gas engine to LPG. How difficult would it be?

I'm a dealer for the new Lehr outboards. It is a new product and we've only got a few out in the field. Time will tell about reliability but it's looking good so far.
The big advantage for me to use LPG (propane) is the carb doesn't gum up between uses. My dinghy gasoline outboard can sit for months without use and every time I want to use it, I have to rebuild the carb. Won't be a problem with LPG. I converted my home portable generator to LPG for just this reason. If you convert a gasoline outboard to LPG you will lose some top end power.The reason is that there are fewer BTU's per gallon in LPG than in Gasoline. How ever an engine that is designed to produce 5 horse power on propane will produce 5 horse power. An engine such as the Lehr, that is designed to run on propane is a little more efficent in using the available BTU's because it can run at a higher compression ratio than a gasoline engine. LPG has an Octane rating of 110. The five hp Lehr outboard will run about half an hour at wot on a pound of propane. That's ten hours on a typical 20 pound tank. LPG produces a lot less carbon monoxide than gasoline. So little in fact that we were allowed to run one inside at the Miami International Boat Show. There is almost no carbon build up in a propane powered engine which I believe will lead to longer life.
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Old 18-05-2012, 16:09   #7
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Re: Convert Gas Engine to LPG. How Difficult Would it Be?

LPG engines in cars will last at least three times longer than gasoline, but require special valves and seats. Some conversions will have a gasoline carburetor (carb) mounted on top of the LPG carb so that dual fuel can be used. The propane is taken off the bottom of the tank so the propane is liquid. A special heater using heat from the engine is used to vaporize the propane; otherwise, the heat of evaporation can freeze up the tank. You can feel what I mean by running your hand down the side of a tank while running a BBQ and feel the tank where it suddenly gets colder. An engine can use so much propane that not enough propane can become available to run the engine and you see where frost forms on the side of the tank. Many RVs will use propane powered generators if the RV is Diesel powered. I have not had any problem with the gasoline carb on my little outboard gumming up with its sitting, but I do run it dry by turning the fuel off and letting the engine run out with the boat tied to the dock. A small residual is left in the carb, but I have never had a problem starting the next Spring. By the way I never use gasoline with alcohol in it as this blend can go bad in several months if not sooner. Also the alcohol will take moisture out of the air and make for difficulties. Alcohol will cause starting problems in my exprience. Premium usually does not have alcohol at least where I live. It seems to me that the engine would have to be a four cycle for LPG where oil in the crankcase would provide the needed lubrication. My last thought is that if the cooking stove uses propane, then there is a ready source for an outboard.
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Old 18-05-2012, 16:50   #8
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Re: Convert gas engine to LPG. How difficult would it be?

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I'm a dealer for the new Lehr outboards.
Snip
So what about service and parts?
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Old 18-05-2012, 20:04   #9
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Re: Convert Gas Engine to LPG. How Difficult Would it Be?

Here is an interesting article about gasoline fueled diesel engines. In the context of this thread think LPG instead of gasoline.

Engine Could Boost Fuel Economy by Half - Technology Review

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Old 18-05-2012, 20:32   #10
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Re: Convert Gas Engine to LPG. How Difficult Would it Be?

SailFastTri, Lehr dealers are being required to stock parts and either have a mechanic on staff or arrange with an outboard repair shop near by to handle the repairs. The engine is just like a regular four stroke outboard except for the propane carb. That isn't a repairable part and if it goes bad will just be replaced. Any mechanic that works on four cycle outboards should be able to work on it. They haven't said so but I suspect that one of the major OB manufactures makes the lower unit and the power head. I'm still learning about these things and don't even have one for myself yet. I'll grab one of the 2.5 hp units to power my canoe and inflatable dinghy. I'm also building a 14 foot stitch and glue plywood skiff that I'll put one of their 10 HP motors on. The 10's aren't available yet but neither is my boat.
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Old 28-09-2014, 21:14   #11
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Re: Convert Gas Engine to LPG. How Difficult Would it Be?

Just thought I'd bump this old thread to see if anyone has something new to add?
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Old 28-09-2014, 22:15   #12
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Re: Convert Gas Engine to LPG. How Difficult Would it Be?

Friend of mine wants to do the great loop on his 34' cruising houseboat. Has a big gasoline engine - maybe two. He did some inquiries and found that while he could convert them to propane, no lpg company will come in to a marina to fill his tank. Something about marine certification and insurance. We're not talking 20lb tanks either.
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Old 28-09-2014, 23:25   #13
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Re: Convert Gas Engine to LPG. How Difficult Would it Be?

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Just thought I'd bump this old thread to see if anyone has something new to add?
Sure, lithium batteries and electric outboards, put an end to your gasoline outboard woes. Run the diesel to charge up the batts.
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