Do Those Fuel Additives Work?

I have a friend who swears by those gasoline additives that claim to increase your gas mileage. I think they’re all worthless. Am I right?

You can understand why people want to believe this type of product works. Wouldn’t it be nice if you could pour an additive or pop a pill into your gas tank at each fill-up that would significantly increase your car’s gas mileage? But fuel additives — both commercial and homebrewed — are almost always a waste of money. With one notable exception (keep reading), these additives simply will not increase your car’s mpg. If you really want better gas mileage, your best bet is to drive a fuel-efficient vehicle, and drive it frugally.

To understand why so many of these additives are ineffective, it’s helpful to understand that all modern engines are controlled by the vehicle’s on-board computer. The computer relies on sensors to adjust engine functions, including fuel delivery, ignition timing and — on the most advanced engines — when the intake and exhaust valves open and close. Mileage-boosting fuel additives claim to increase the combustion efficiency of gasoline. But the automaker programs a vehicle’s computer to have optimal fuel economy with straight gasoline in the tank. Change the chemistry, and you may actually find a decrease in both performance and mpg — if there is any real change at all. Also, consider this: If there really were safe, cost-effective additives to increase fuel economy, wouldn’t some gasoline brands already be trying to sell them to you (along with their gas)?

This is a “buyer beware” scenario. Some of these mpg additives come wrapped in elaborate marketing schemes designed to play on our desires to one-up Big Oil, save money and do the right thing for the environment. Don’t buy it. Don’t believe glowing user testimonials either. If these testimonials have any degree of truth, any actual changes in mileage after using mpg-enhancing additives are more likely due to a change in driving style than to the effects of the additive. A strong placebo effect can happen when people really want these additives to work in order to justify the expense. That enhanced motivation makes a driver pay more attention to driving efficiently, and the results are predictable. (Affecting your mileage through your driving habits is easier than many people realize. I evaluate cars and trucks for a living, and I can easily alter the fuel economy of a vehicle by as much as 25 to 30 percent by the way I drive it.)

You’ll also find some people who swear by homemade concoctions to increase fuel economy. Acetone, sometimes mixed with other chemicals, is a popular DIY fuel economy enhancer. This mpg trick may have other consequences however, such as shortening the life of your vehicle’s seals and gaskets, and perhaps harming the emission control sensors.