Propane vs. Butane in a Lehr propane outboard

[Roy M]

The Lehr motors use propane which has an octane rating of 110. The engines are built for a higher compression load. Your car uses fuel with an octane of 80-something, assuming it's gasoline. If anyone wants to compare performance and lives near San Diego Bay, I'm sure we can arrange some drag races, then pay for filling the tank afterwards. My fuel tank is a composite fiberglass forklift tank, 7+ gallons, horizontal, delivering liquid propane to the carburetor. I am waiting for an aluminum "Whale Tail" fin to add to the cavitation plate to make it an even hotter performer.

[HopCar]

"If I think about it, my 2.5 may run on liquid sometimes, because the bottle is horizontal, and I assume that a full 1lb bottle is more than half full."

Exactly right. In fact all of the Lehrs are happy to run on liquid propane but they vaporize it before it enters the cylinder. With the 2.5 that happens in the fuel line. The larger engines all have water warmed vaporizers.

A regular barbeque tank sitting upright will deliver propane vapor but it is limited as to how much it can deliver by the size of the hose and how fast the propane can boil in the tank.

Turn the tank upside down (not safe) and it will shoot propane liquid through the hose which can be vaporized into a much greater volume of vapor than could be delivered by the hose. The fifteen will run on propane vapor from a barbeque tank but not at full speed. Fork lift tanks are designed with the pick up in the bottom of the tank and safely deliver liquid propane.

[a64pilot]

What is unsafe about turning a grill bottle upside down? That is exactly how I get liquid freon when appropriate.

[HopCar]

"I've wondered why some that seem to want a propane powered outboard don't simply convert their Honda or other four stroke to propane? Myself I'd rather have the Honda, especially if I already had it."

There is no reason you can't. In fact if someone made a kit to do it, they'd probably sell some.

The problem is that you lose power when you convert a gasoline engine to propane.
A 5 hp gasoline engine converted to propane might put out 4 to 4.5 hp but a 5 hp Lehr puts out 5 hp.

The Lehr engine is designed to run on propane and has higher compression to take advantage of the higher octane of propane. You couldn't convert a Lehr to gasoline without lowering the compression somehow.

[HopCar]

"What is unsafe about turning a grill bottle upside down? That is exactly how I get liquid freon when appropriate."

A64, the problem is that when you turn a barbeque propane tank upside down, the overpressure relief will vent liquid propane instead of vapor as it should. I'll leave it up to you to decide if that is a real danger. The propane industry say it is dangerous. My lawyer would be unhappy if I recommended doing it.

[a64pilot]

Not being very smart, I'd think venting propane is dangerous, liquid or vapor.
You have me curious as I don't know how the overfill device works, it's a pressure relief valve? That would indeed be stupid, these tanks are not dewars.
In either respect a venting overpressure relief valve is an indicator of impending doom or a bad valve, you have had one vent?

[HopCar]

The over fill device and the over pressure vent are two different things.

The over fill device is a float valve just like in a toilet. As the liquid level rises in the tank the OFD closes the inlet and won't let any more into the tank.

The over pressure vent is designed to vent vapor if the tank is in danger of exploding.
The tank generally needs to be in a fire for this to happen. In a fire the propane industry feels it's better to vent vapor rather than liquid. Either way, you get a hell of a torch but with luck you avoid an explosion.

[a64pilot]

I figured pretty quick that the OPV and OPD were maybe in the same body, but different.
I had thought maybe that the OPV might be a burst disk and not a pop off valve, but a burst disk with flammable gas would be stupid.
Still very unlikely to let go unless seriously over pressurized like in a fire like you say,
but stuff happens, things do break, especially near salt water.

[Roy M]

Now, having a Honda generator that ran on propane......... I would really like that combo for a whole bunch of reasons. Lehr, got your ears on?

[HopCar]

Roy, I've been telling them the same thing. If you're willing to accept a loss of some power, I think there are conversion kits for the generator.

[Roy M]

Parks, tell them that there is also a market for propane powered emergency bilge pumps. We have a gasoline powered Honda unit in our emergency locker at our yacht club. To be able to avoid regular startups and preventive maintenance would be a great time-saver. The Coasties would probably also be interested in something that reduced the insecurity of long storage and infrequent use.

[HopCar]

Roy, That just makes too much sense. I will pass on the suggestion. Not only is a propane powered pump more likely to start when you need it, you can store the fuel indefinitely without it going bad.

[SailFastTri]

I converted a generator to run on natural gas and it works great -- would love to have a quality dinghy outboard that runs on LP. From the scuttlebutt online that rules out Lehr.

I started to think about the conversion then came accross TruFuel. I bought some and don't have experience with it yet (so can't recommend it). But the cost of a LP conversion plus tanks and hoses is around $150+ but TruFuel is just very expensive gas that doesn't go bad. For small engines that aren't used frequently it makes a lot of sense. Dinghy motors under 8hp, snow throwers, emergency backup generators, etc. Larger engines that burn more fuel or are run for extended periods, not so much.

[Roy M]

SailFastTri, maybe you should convert your outboard to natural gas, since you are apparently only confident in your own experience. Be sure to bring along an extra can of beans, though. Seriously, try the Lehr before you condemn them. You are really missing the boat.

[SailFastTri]

Originally Posted by Roy M

SailFastTri, maybe you should convert your outboard to natural gas, since you are apparently only confident in your own experience. Be sure to bring along an extra can of beans, though. Seriously, try the Lehr before you condemn them. You are really missing the boat.

If I was only confident in my own experience I'd buy the Lehr and try it. Unfortunately I've read many posts about QC issues with Lehr engines, not to mention a few private conversations and emails with others who have experience with them. It doesn't inspire confidence.

This summer I used gas in my dinghy outboards (two of them) with no issues. Would I like to swap for LP? You bet. But I don't just want to swap one problem for another. I wrote elsewhere that if I have a problem with a fouled carb there isn't any marina that doesn't have someone who can fix it if I can't. However, if I had a Lehr and it fails I'm SOL.

That's the concern, and (until I start reading more about how RELIABLE and problem free these things are) I'm hoping that a mainstream maker (e.g. Tohatsu, Yamaha, Honda etc.) will come out with an LP outboard.