Is alcohol in gasoline good or bad? Is there a difference between ethanol and methanol?

Dear Cecil: Stopping at a local gas station and seeing a large banner announcing “Alcohol Free!” reminded me that there was some controversy surrounding the use of ethanol versus methanol in gasoline. What are the differences between these two octane boosters? Danglin’ Dave, Garland, Texas

Cecil replies:

It may be OK to dangle out there in Garland, Dave, but here in the big city we’d prefer that you buttoned up. As for alcohol, there are some differences between ethanol (made from grain) and methanol (made from methane). But the real question is whether you want to use gasoline laced with alcohol at all, since it tends to screw up your engine.

Many refiners began putting up to 10 percent alcohol (usually ethanol) in their gasoline in the 70s, producing what’s known as gasohol. It’s most commonly available in the Midwest, particularly in Farm Belt states where it’s subsidized in the form of lower taxes, but you can also find it in the West and South and occasionally elsewhere. Alcohol has two advantages: it’s a renewable resource, unlike petroleum, and it boosts octane, meaning you’ll get less pinging and knock. Methanol has the added advantage of being quite cheap.

In fact, alcohol would be just about perfect were it not for the fact that it can soften hoses and gaskets, dissolve your carburetor float and other plastic parts, and corrode metal. It can also cause vapor lock and hot-weather restarting problems, and it tends to lower your gas mileage. Methanol is the more serious offender, but ethanol will give you trouble too.

Unfortunately, it’s not always easy to tell whether gas contains alcohol. Amoco used to put decals on some of its pumps saying “Pure Lead-Free, No Alcohol Added,” but now the no-alcohol line is being dropped, in part due to protests from gasohol advocates. Amoco pumps that do have gasohol are prominently labeled, but this is not necessarily the case with all retailers.

Most major refiners that sell gasohol use ethanol rather than methanol. ARCO (Atlantic Richfield) for a long time was the exception, but the company eventually discontinued the sale of its methanol blend. You may still wind up with some of the stuff, however, because unscrupulous service station operators have been known to cut their gas with methanol in order to chisel a few extra bucks. If you’ve been having inexplicable problems with your ride lately, try filling your tank at a different joint.

Cecil Adams

Send questions to Cecil via cecil@straightdope.com.