BroadBand
Since late 60's
Myth: Ethanol-enhanced gasoline (E10) loses octane much faster than regular gasoline.
Many mechanics believe that octane loss during winter storage could be great enough to damage an engine when it's run in the spring. These same mechanics will often recommend leaving the tank almost empty so that fresh gasoline can be added in the spring to raise depleted octane levels. While all gasoline loses octane as it ages, ethanol-enhanced gasoline loses octane at about the same rate as regular gasoline, according to Jim Simnick, a technical advisor at BP Global Fuels Technology, and Lew Gibbs, a senior engineering consultant and Chevron Fellow. The two men have over 75 years of combined experience working with gasoline and both agree that the loss of octane over the winter would not be sufficient to damage an engine. Note, however, to keep any gasoline, including E10, as fresh as possible; they said it's good practice to always add fuel stabilizer — an antioxidant — whenever the car/boat/motorcycle/engine will be idle for long periods.
The recommendation to leave a tank mostly empty is bad advice; it could significantly increase the amount of water that gets into the tank. When enough water enters through the vent, the ethanol will separate ("phase separate") from the gasoline. Leaving a tank mostly empty does three things to increase the chances of phase separation:
It increases the volume of open space in the tank (its "lung capacity") so it can "breathe in" damaging moist air. An almost-empty tank leaves more space on tank walls for condensation to form. Leaving less gasoline in the tank means there will be less ethanol to absorb the condensation.
It's interesting to note that in areas of the Midwest that have been dealing with E10 for over a decade, topping off tanks is common practice.
If phase separation occurs, the highly corrosive ethanol/water mixture will settle to the bottom of the tank and remain there even after fresh fuel is added in the spring. The only way to remedy the problem would then be to drain the tank and add fresh gasoline. The best way to avoid phase separation over the winter (aside from emptying the tank) is to leave the tank 95-percent full (which allows for expansion) so that there's less moist air in the tank, less space for condensation to collect, and more gasoline to absorb whatever moisture does accumulate.
Many mechanics believe that octane loss during winter storage could be great enough to damage an engine when it's run in the spring. These same mechanics will often recommend leaving the tank almost empty so that fresh gasoline can be added in the spring to raise depleted octane levels. While all gasoline loses octane as it ages, ethanol-enhanced gasoline loses octane at about the same rate as regular gasoline, according to Jim Simnick, a technical advisor at BP Global Fuels Technology, and Lew Gibbs, a senior engineering consultant and Chevron Fellow. The two men have over 75 years of combined experience working with gasoline and both agree that the loss of octane over the winter would not be sufficient to damage an engine. Note, however, to keep any gasoline, including E10, as fresh as possible; they said it's good practice to always add fuel stabilizer — an antioxidant — whenever the car/boat/motorcycle/engine will be idle for long periods.
The recommendation to leave a tank mostly empty is bad advice; it could significantly increase the amount of water that gets into the tank. When enough water enters through the vent, the ethanol will separate ("phase separate") from the gasoline. Leaving a tank mostly empty does three things to increase the chances of phase separation:
It increases the volume of open space in the tank (its "lung capacity") so it can "breathe in" damaging moist air. An almost-empty tank leaves more space on tank walls for condensation to form. Leaving less gasoline in the tank means there will be less ethanol to absorb the condensation.
It's interesting to note that in areas of the Midwest that have been dealing with E10 for over a decade, topping off tanks is common practice.
If phase separation occurs, the highly corrosive ethanol/water mixture will settle to the bottom of the tank and remain there even after fresh fuel is added in the spring. The only way to remedy the problem would then be to drain the tank and add fresh gasoline. The best way to avoid phase separation over the winter (aside from emptying the tank) is to leave the tank 95-percent full (which allows for expansion) so that there's less moist air in the tank, less space for condensation to collect, and more gasoline to absorb whatever moisture does accumulate.