Can I really burn used vegetable oil in my car?

This bottle of used cooking oil was used to fill the gas tank of the converted 1984 Mercedes Benz 300 Turbo Diesel. See more alternative fuel vehicle pictures.

It would be nice if we could find a new kind of fuel to use in our cars, something that gives us good mileage and doesn't cost much. What if we could use some common and easily available substance for fuel? What if we can use a substance that no one really wants: If they're going to throw it away, they'd probably just give it to us if we asked, right?

Free fuel would be great - if we could get it. Incredibly, that's exactly what some people are getting by using vegetable oil in their cars. Most restaurants just throw the stuff away when they're done cooking with it, so veggie fuel fans work out deals with their local eateries to come by periodically to pick up batches of old oil. Does it even matter what kind of mileage you get when the fuel is free?

Of course there's a catch: You can't just dump vegetable oil into your tank and drive off into the sunset. You'll ruin your engine. It's also not a guarantee that a vegetable oil-based energy policy would work on a nationwide scale; however, it does provide another alternative to expensive and increasingly scarce fossil fuels.

To learn how we can fill up our gas tanks with last night's chicken grease, we must first learn to distinguish between vegetable oils used as fuels and biodiesel. Biodiesel is a type of fuel derived from vegetable sources, often soy, but is refined at a special facility which must follow anti-pollution laws and other fuel regulations. Many vehicles with diesel engines can run on biodiesel or a blend of biodiesel and petroleum diesel without much modification [source: National Biodiesel Board].

Using vegetable oil to fuel a vehicle is an entirely different matter. You're basically using the vegetable oil you can buy at the supermarket (or get for free from a restaurant) as fuel. It's more of a do-it-yourself type of alternative fuel. It doesn't go through any refining process and it isn't regulated or tested according to environmental laws. In fact, using this type of fuel could be illegal in some states, as state and federal revenue agents in the U.S. require special licenses to drive the converted cars as well as payment of motor fuel taxes [source:Freeman].

How do we actually use vegetable oil to power our cars? Let's dig in on the next page.