What is the Effect of Ethanol and Gas
Mix on Outboard Motors
There is a great deal of talk about ethanol and gas mixtures damaging boats and causing problems. Ethanol has been with us for a few years now and information is not as bleak as predicted. There are things you should know about ethanol gas blends though.
Why is ethanol added to gas
Adding Ethanol to gasoline provides several benefits.
- Ethanol mixtures lower carbon dioxide and carbon monoxide emission.
- Fewer volatile compounds are produced from evaporation (such as when the car is refueled).
- It is said to improve fuel octane.
- Lower levels of hydrocarbon and nitrogen oxides are emitted.
- Because ethanol is produced locally and not imported it reduces the quantity of gas that needs to be imported.
- The production of ethanol is of economic importance. It helps support farmers and bring up their revenue. The down side of this is that it does compete with other uses of the corn such as food production. Widespread use of increasing amounts of ethanol is likely to bring up food prices.
- Ethanol is not a fossil fuel and thus is a renewable resource. It is NOT pollution free, however since agriculture is a major source of pollution, and has a major impact on the environment.
- These benefits are diluted somewhat by the lower energy content of Ethanol. It is only 66% as energetic as Gasoline so it takes more alcohol/gas to go the same distance that gas alone can go.
What effect does ethanol have on motors
Other than a reduction of gas mileage, modern cars, used regularly, will not suffer huge damage. They have been designed to be able to deal with the mix. Older cars, 2 stroke engines and 4 stroke small engines can run into problems.
A large proportion of the problems reported is due to the tendency of Gas/Alcohol blends to separate. It's referred to as Phase separation. Also the gas/ethanol absorbs water and when it separates the water residue can corrode, rust or damage engine parts. Damage to rubber, plastic and fiberglass is widespread. This corrosion creates further residues which can gum up and block valves and openings. Carburetors jets can be affected by this. The gum and varnish can coat engine parts and reduce performance. The compromised gas/Ethanol can also interfere with the lubrication of the 2 stroke engines.
Gas alone has a limited shelf life and goes "bad" if not used up in this period. Fuel oxidation is the problem. The addition of Ethanol shortens this shelf life.
A story that went around in my boat club was about a jar of gas that a marina kept on its counter. Even though it was only a few weeks old it had separated in 2 layers. It was shown as an argument to use only ethanol free gas, which the marina sold at a premium.
Outboard motors are particularly sensitive to problems dealing with gas mixed with ethanol. The gas will often sit around for long periods, and is often exposed to high humidity conditions. For that reason it is not unusual for outboards to accumulate water in the system. My 6HP Mercury has a small filter that is intended to trap stuff including water before it reaches the cylinder.
When water is in the gas it makes the motor run rough and cut out, idle badly particularly at low speed, causes corrosion and damage, and can make a motor hugely difficult to start.
What can a boat owner do to avoid damaging his outboard motor and help it run and start better?
Poor Gas can make it hard to start your motor and make it run poorly, this will help.
1. IF you can find alcohol free gas then use that. Often gas companies will offer one high octane gas which is alcohol free.
Here is a link to Canadian and US gas stations that offer alcohol free gas. If the alcohol content is not marked then choose the high octane fuel, it is more likely to be alcohol free if the attendant doesn't know find out from the company for next time.
2. Use a gas stabilizer. There are countless versions available. Ask you outboard dealer what they recommend. Use it religiously.
3. Don't let gas sit for long periods. Many sailors will buy a tank of gas and use it all season. It's better to take the gas home after a couple of months, use it up in the car and get another can of fresh gas, with stabilizer of course.
4. Another thing you can do is disconnect the gas line, or turn off the gas valve, while the motor is still running and let it run dry to use up all the gas in the engine and not have gas separating in the engine. Check with your dealer to see if it's recommended for your engine. Mine was happy with this procedure.
It's not a bad idea to check your little gas line filter to see if it's picking up water. If it is, change your gas and clean out your motor.
4 Stroke engines are trickier than the old reliable 2 strokes. They need to be properly maintained, with good spark plugs, and fresh gas as much as possible.
The above has been my procedure for 2+ years and my engine has not given me any grief ever. It was very difficult to start when I first got it and I suspect that it had sat at the dealer for a season and for this reason was difficult to start. Once it cleared out whatever was bothering it it has started on the first pull every time, except when I flooded it. sigh.
I don't claim to be an expert, but when I was having trouble starting my new motor, and it was running very poorly, I laid my soul bare to any mechanic who would listen. I also haunted and lurked in countless forums. Advice was mixed but the more reliable guys recommended the good gas, stabilizer, replace often, and run dry routine. My brother is a mechanic and he agreed with the procedure. He also stressed that it is important to break in the motor properly if it's new. It will run rough until then.
Please note than I am not opposed to alcohol being added to the fuel for cars. I support any environmental responsible initiative. It's just not very good for an outboard at this point.
email me if you find mistakes, I'll fix them and we'll all benefit: Christine