Q: I learned the hard way that lawnmower gas goes stale over the winter, so now I use gasoline additive in my mower, string trimmer, snow blower, and generator. But my neighbor says it’s better to burn the tank dry. Is that true?
The reason that gas gets “stale” and can gum up power equipment engines is that it contains ethanol, which absorbs water. That water can damage the engines of non-road equipment, says Kris Kiser, of the Outdoor Power Equipment Institute, a trade association.
Most gas-station gas contains 10% ethanol, thanks to a 2007 federal mandate designed to reduce carbon emissions. And 15% ethanol is now being sold at some stations, but only for cars built in 2001 or later.
It actually turns out that ethanol doesn’t provide nearly the environmental benefit that was expected—and some lawmakers are proposing eliminating the mandate altogether—but that’s another story. For now, the vast majority of small-engine problems can be traced to ethanol, says Kiser, and you have three choices for avoiding trouble:
- Buy ethanol-free fuel. You can get it at home centers and outdoor power equipment dealers. Burn it and you won’t have to worry about your gas going stale. The problem is you’ll pay around $6 a quart for “E-0” gas. That equates to a very steep $24 a gallon.
- Use a fuel stabilizer. It prevents the ethanol from absorbing moisture and thereby prevents regular gas-station fuel from going stale and gumming up the motor. A bottle that costs only about $9 will probably last you several years.
- Run your gas tank dry. By rationing small portions of gasoline into your power equipment as needed and always running the machines until they burn all that gas and stall out, you ensure that no gas is left in the engine to go stale. This solves the problem and offers another large benefit, especially for gas-powered generators. The standard advice to run generators monthly is largely designed to burn the old gas and prevent it from going stale. But if you leave the tank dry, there’s no need to do that. Just start it (with very little gas) every few months to ensure it’s working properly, and run it until the gas is gone.
“Any of these three options works well,” says Kiser, “but check your owner’s manuals because different manufacturers have different requirements for their machines.”