Make and Make Do

By Rob Rohde-Szudy - Madison, Wisconsin - USA


Ethanol in two-stroke outboards

Last time we talked about some modifications we could make on old two-stroke outboards to clean them up. Now let’s look at making those modifications even more effective with a cleaner fuel.

Ethanol is that fuel. Since it is infinitely soluble in water – that is, soluble at any ratio – a small amount of fuel would dissipate relatively harmlessly rather than collect on the surface and choke off the oxygen exchange that aquatic life needs. Ethanol offers other advantages like being 100% made in the USA, being an oxidizing fuel, and reducing combustion chamber temperatures. The latter is why race engines burn alcohol, even though they use (toxic) methanol.


But how do we get two-stroke oil to dissolve in ethanol? It won’t. At least cheap petroleum oil won’t do it. But expensive synthetic oil will.

So let’s talk about what synthetic 2-stroke oil is. Don’t be confused by labeling. Some of the stuff they call “synthetic” is really just highly modified petroleum oil. This is not the same thing. We are talking about fully synthetic ester-based oil.

“Ester” should be a clue to those who know a little chemistry. These “fully synthetic” oils are esters of vegetable oils. In a word, biodiesel!

For simplicity and comparability, though, I conducted these experiments with AMSOIL Saber Outboard, an ester-based synthetic ester oil. At around $8 per quart it is rather expensive, but it comes out comparable or cheaper than petroleum oil when you consider that you only need half as much. I also think they add something to this oil to help it cling to the moving parts better, so maybe it’s worth the money anyway. (Note: don’t confuse this with AMSOIL Saber Professional, which is not rated for marine use. It matters.)

In case you were wondering, I’m in no way connected to the AMSOIL people. I only went with this product because a casual internet search led me to believe they’ve done the most work on applying synthetic technology to outboard oil. And being a major name in racing oil, it should be easy to find a dealer wherever you are. But I’m pretty sure any synthetic ester oil that’s meant for outboards would be fine.

I should note that AMSOIL only officially recommends this oil for use in gasoline of no more than 10% ethanol. Apparently this is because it can separate into layers if left sitting still for a long time. The solution is simple – shake the tank before use. If you are towing the boat to the water, this is highly unlikely to be a problem. Keep your fuel free of water – water makes it much harder to keep the oil from separating. I recommend venting the tank periodically, rather than leaving the vent open. Less chance for water to get in.

Fuel:Oil Ratio

So how much ester oil should we use? AMSOIL Saber Outboard recommends 100:1 on the label. This is for newer engines that are made for 50:1, and these old outboards require about double that. Since the idea is that you need half as much, I use half of what OMC recommended with regular outboard oil. In 1955, they said 24:1, so I started with 48:1. I suppose there is some leeway here, since the factory ratio is meant for 30w automotive oil. Even mineral-based modern 2-stroke oils are much better than 30w auto oil.

But there’s a wrinkle. There is some question as to the relative lubricity of gasoline and ethanol. There is little research and even less agreement as to whether gasoline or ethanol has better lubricity. One would think that gasoline has some lubricity and ethanol almost none. But some of the limited research has found that ethanol “blends” (which might be E-10) better lubricity in two-stroke engines.

The bottom line is that we have to trust our own observations over anything we read from someone who might have an agenda. 48:1 actually seemed to work fine, but I was concerned as to whether it would stay OK in storage. Ethanol is a good solvent and might wash the oil out of the bearings. At 48:1 the motor felt a little tight after sitting for a week, so I switched to 40:1. It seems a little better now, but I still feel like I need to use fogging oil if I’m storing it more than a week. This might be paranoia, but in the absence of reliable data, paranoia is not all bad. I’d rather use fogging oil than increase the oil in the gas any further, because at least the fogging oil burns off and then it’s done with. The oil in the gas is always there, so we should keep it to the practical minimum.

At 40:1 we still get a cloud of smoke, but now it’s white and doesn’t smell nearly as acrid as the blue petroleum cloud. But you can also get fooled by the new smell. The ester oil burns with an aroma reminiscent of hot metal. Don’t panic. Feel your waste cooling water to determine whether you’re truly running hot.


“So, what, do you brew this stuff?” You could, but it’s a pain in the butt and in the USA it requires a license from the Bureau of Alcohol Tobacco and Firearms. I wouldn’t bother.

Fortunately, many urban areas have a gas station that carries E-85. This is simply 85% anhydrous (no water) ethanol and 15% gasoline. Apparently a number of cars made since 2000 were designed with the ability to burn E-85 just as easily as gasoline. E-85 costs about the same as regular gasoline (this might change as petroleum gets scarcer) and reduces hydrocarbon emissions about 85%. The latter is of course completely predictable, since E-85 contains 85% less hydrocarbon than gasoline. The government will help you find sources at.

Work on the engine


First and foremost, check your compression. This isn’t going to work in a motor with marginal compression. It should be about 80 to about 100 psi. If it’s low, a new head gasket might fix it. But don’t do this unless you have to and take all precautions against breaking off the bolts in the casting! It’s easy to do and hard to fix.

Fuel system

You may have read articles about ethanol in cars, which can require some relatively extensive modifications. In particular, the carburetor’s jets need to be bigger. (If you have injection you need a kit for around $600.) Here we have it very easy with simple old engines. We don’t have fixed jets, so we just open the mixture screws a bit when running alcohol. Isn’t low-tech great?

But you should consider rebuilding that old engine’s fuel system if you haven’t already. Natural rubber gaskets from the old days can’t tolerate alcohols, but modern synthetic rubber can. Besides, it’s cheap and we’re only talking about 3 hours or so. Max’s articles or his book (Cheap Outboards) can guide you there.

One final thing to consider is your fuel tank. Steel tanks tend to rust faster with ethanol. I’d get a cheap plastic tank, which will last about forever with any fuel if you keep it out of sunlight. If you have a pressure tank engine, this might be a good time to convert it to a fuel pump. Again, Max’s book is the best resource out there.

At the same time as upgrading fuel system parts, you might also replace the rubber oil line on the side of the crankcase. If it’s original – and it probably is – it won’t handle ethanol for long.


Ethanol is less flammable volatile that gasoline and needs a blue-hot spark to ignite. This demands the ignition be in top condition. Anything less than a bright blue SNAP won’t cut it. If you have trouble with igniting the ethanol, consider hotter spark plugs. But first try brand new fresh plugs of normal specs and check the points for condition and gap. And remember that with a magneto ignition, cranking faster makes a hotter spark.

In the articles on automotive ethanol conversions, they recommend advancing the spark a bit. I didn’t find that to be necessary in this case.


Seals are one thing that worries me here. I didn’t bother to replace any of the seals in the engine, and I don’t know what they’re made of. If they are not alcohol-resistant, they will eventually fail and I will have to rebuild the powerhead. Here I am mostly talking about the crankcase shaft seals, and replacing them involves pretty close to a full rebuild. On the other hand, this is probably not terribly difficult on a motor with so few moving parts. (Famous last words…)

Starting primer

Since ethanol is less volatile than gasoline, it needs more heat to vaporize. Cold starting might be a challenge in cold weather. The simple way around this is to carry a small bottle of gasoline/oil mix and squirt some in the air intake if you need to. Fortunately, using E-85 it seems fine without a primer in any weather nice enough for me to be boating. I suppose the gasoline parts vaporize fast enough to get it going.

How to run the engine on Ethanol

There are not many differences, but let’s run through the process as if this is the first time we’re trying ethanol.

• Fill the tank with E-85/synthetic oil 40:1 mix – 3.2 oz per gallon. Or do it the smart way. A gallon is 3,785.4 mL. So 96.6 mL of oil per gallon of E-85. Use a syringe if you haven’t made a calibrated measure.

• Shake well before use.

• Back out the high-speed mixture screw about ¼ turn from where it works well with gasoline. You’ll refine this as you run it.

• Prime the fuel line as normal.

• Turn up the throttle to the “start” range, choke like normal, and pull the struggle string. When you pull it, gently engage the pawls, then pull the cord briskly. Too slow and the spark won’t be hot enough. It should fire in three pulls or less, just like with gasoline. Don’t bother to go past 6 pulls.

• If it doesn’t start, try a squirt of gasoline mixture in the air intake.

• If it doesn’t start in three pulls after that, something else is wrong.

• Once it’s running, open the choke. I find I have to baby the choke a little longer than with gasoline – just a couple seconds. Then I have to turn the throttle up a little higher than with gasoline to keep it running. After less than a minute of warm-up, I can use any rpm.

• Adjust the high-speed mixture when you’re up and running, then the low speed mixture when you have it warmed up and return to idle. (Just like that worn-off print on the cowling says.)

That’s all there is to it.


Less smoke – At least nicer smoke. Not the acrid, choking smoke I used to have.

Less plug fouling – surely a function of less oil.

No carbon fouling – It might be my imagination, but this stuff seems to have removed some carbon fouling from the engine. Maybe I can get rich selling ethanol as an engine cleaner.

Less water pollution – The usually oily sheen at idle is barely perceptible. And the oil that is present is biodiesel, which is more biodegradable. Ethanol itself is also relatively biodegradable in water, and it forms no oxygen-blocking film because it dissolves in water and dissipates rapidly. Check out samples of the water from identical barrel-testing runs.

Here’s the gasoline mix

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And the E-85 mix. One part of the bucket got oilier, so I show the oily spot and the less oily part in separate photos.

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These water samples came from running starting up the motor in a new 5 gallon plastic bucket filled almost to the top, idling 5 minutes, running 10 minutes in gear at halfway between “start” and “fast”, then shutting down and immediately photographing the sample. The visible difference is readily apparent. It smells like a weak martini with ultra-cheap vodka, which is a distinct step up from the stomach-turning aroma of the former “petro-mayonnaise”.

Now this is not 100% fair, since in the above results the ethanol has the advantage of the crankcase bleeder bypass. Let’s level the playing field. This is how much waste fuel the bleeder collected during the test run.

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And here’s the bucket with the bleeder waste stirred in.

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This isn’t exactly laboratory water testing, but the results speak for themselves, I’d say. Especially since ethanol and ester oil are more readily biodegradable than their petroleum counterparts.

Broader Implications

There’s more to this than simply reducing emissions of some “obsolete” outboards. In fact these motors are no longer “obsolete” if their emissions are brought in line with modern expectations. Not only does this allow poor people like me to be more environmentally conscious, but it also reduces the need for new motors. It takes a tremendous amount of energy to refine, cast, machine and assemble that aluminum into a motor. So getting more use out of the motors we have means less energy used, less oil drilled, and less greenhouse gas for the same end use served.

Even better, our new power source is not based (predominantly) on petroleum, whose carbon has been locked up for millions of years. It’s based on corn and soy that were grown last year. This means very little net disturbance to the carbon cycle. You can almost view it as liquid solar energy. The only way to go boating with less impact is to row or sail.

Finally, nobody’s kids or parents have to go off to the Middle East to get shot at to secure access to Ethanol or soy oil. They come from farmers right here in the USA who desperately need the market. Why should tax dollars pay our farmers not to grow crops when we could be using these folks’ skills to grow our own energy? Growing our own fuel paves the way for real economic stability and national security. This is true even if you think there’s a lot of oil left, and it lets us save that oil for purposes where there is no currently viable alternative. I’d rather make that oil into epoxy than burn it. (Until they come up with soy epoxy, anyway…)

In that light, I hope this work is a small step toward a much greater goal. Either way, it sure makes me feel better about running that old outboard.

Rob Rohde-Szudy
Madison, Wisconsin, USA

A version of this article with fewer photos but further discussion can be found in the October 15, 2006 Issue (Vol 24 - #11) of Messing About In Boats.

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