Which Fuel

[dfeste]

I normally run nonoxygenated in all of my small engines as well as the fuel injected four wheeler. I was under the impression that this fuel would leave less deposits and run cleaner than the lower octane oxygenated fuels. I just read in another post that the higher octane gas may actually be robbing the engine of power. I spend good money on my equipment and want to take care of it the best I can so what fuel should I be running? I do run Amsoil Sabre at about 80:1 in my two stroke auger. The rest of my small engines are four strokes.

Thanks Dave

[BobT]

For performance' sake if your engine is designed and tuned to run on 87 octane, running it on higher octane will decrease performance slightly. This is because higher octane fuel is a bit more stable than the lower octane fuel and is less prone to pre-ignition. The result is that running it in an engine designed and tuned for low octane it will retard your timing slightly. This is why it sometimes quiets engine ping by using higher octane fuel. That engine pings because the fuel is pre-igniting (early). You can get a similar ping by advancing your engine timing too far.

My 2001 truck manual said to use 87 octane fuel. It said using higher octane fuels will reduce engine performance. This proved to be true and also proved to reduce engine efficiency quite a bit. When I used high octane fuel my economy dropped by nearly 20%.

Being more stable, higher octane fuel has a longer shelf life so many like to use it for this reason. Fuel gets old over time and can actually become non-flammable to some degree and can leave sludge deposits behind. I had some gasoline one time that did this and I poured it into a metal bowl and tried to light it with a match and it would not burn.

There are also those who claim higher octane non-oxygenated fuels are less likely to accumulate water in the fuel. I question this because before we had alcohol-blended fuels, the one thing we put in the fuel to handle the moisture (de-icer) was alcohol.

My experience has been somewhat different. I use 87 octane, 10% blended fuel in everything except my ATV in the dead of summer. I leave fuel for my chain saw in a plastic jug in my shed and have used fuel that was years old (don't really know how old) without any problems. I don't use stabilizers however this winter I did put in a fuel conditioner as recommended by the manufacturer for my new E-Tec outboard. I fill up the tank on my tiller about once every three years and use the same gas. My lawn mowers currently have whatever gasoline was left in their tanks last fall. I used my weed whip once last year and it still has whatever gasoline was in the tank. I don't have problems this way but there are those who would claim I'm running on borrowed time. Maybe, but how long have I been borrowing that time? Since about 1975. That's my experience for what it's worth.

Edit: I should add that I do occasionally throw in a little carburator cleaner.

[hydro]

Dave,

If what you are doing now is working for you, keep doing it. My comment on the higher octane is based on research and 91 octane fuel is certainly not needed for any engine not specifically requiring it. The difference in power output is small (but can be critical, for instance if you are in some competitive race), but I think the biggest advantage for the non-oxygenated fuels is for storage as they have proven to be more stable over long periods, like off season storage. Unfortunately I seriously doubt you will find non-oxygenated 87 octane fuel in the midwest.

Interestingly, the mindset that leaner oil mixtures will make more power also appears to be false. In controlled studies of two stroke motorcycle engines (The ones the factory guy's race), mixtures around 32:1 made the most power on the dyno. Apparently the oil is functioning as fuel at that ratio. A minor difference but worth considering. Personally, I have used the 80:1 to 100:1 ratios in my engines and they do appear to start better and experience less plug fouling, so there are advantages both ways.

Myself, I run the 87 octane gasoline (with the ethanol) in my boat, auger, chain saws, lawn mower, etc., and have never had a problem that I can trace back to the oxygenated fuel. Just keep the fuel fresh, and if you are putting the engine away for seasonal storage, then run some non-oxy fuel and stabilizer into it for insurance.

[harvey lee]

+1 Hydro.

[BobT]

I neglected to explain why I use non-oxygenated fuel in my ATV during the heat of summer. My ATV engine is air cooled without a fan for force airflow. If I'm trail riding and moving rather slow, that engine can get rather warm and the added heat will cause fuel pre-ignition. Using non-oxygenated (off-road 92 octane) helps in this situation because the fuel is more stable and less prone to pre-ignition. If it wasn't for that, I'd use 87 octane year around.