Car Talk's Guide to Alternative Fuels

That's right. You can actually run your diesel car on vegetable oil. The same stuff your local Chinese restaurant is using to whip up your order of General Tso's compressed chicken parts.

The use of vegetable oil -- either straight vegetable oil (that's "SVO" to the self-righteous, eco-cognoscenti) from the grocer's shelf, or waste vegetable oil ("WVO") obtained from local restaurants -- was pioneered by environmentalists in the "grease car" or "veggie car" movement.

You're telling me I can run my car on vegetable oil?

Pretty much -- with two big caveats: First, your car needs to be diesel-powered to begin with. Second, vegetable oil tends to congeal when the weather gets cool – think of what happens to chicken fat in your refrigerator -- which means you'll need to undertake some major modifications (see below) you wouldn't need if you were burning processed biodiesel.

Will any diesel vehicle run on veggie oil?

Yes, if you make all the modifications needed. There are a handful of companies that supply kits or already converted vehicles.

Who's selling a diesel in the U.S. these days?

It used to be that Mercedes, Volkswagen and Jeep were the only go-to companies producing new diesel passenger vehicles in the U.S., but as diesels have dramatically improved, so has the range of available models, even hybrids. It should be pointed out that today's pump diesel is very clean, thanks to new federal regulations. Chevrolet has just introduced a clean diesel version of the Cruze that gets as much as 50 mpg (though diesel fuel remains more expensive than gasoline). Mercedes, in the diesel business since 1936, says its new BlueTEC diesels reduce greenhouse emissions by 30 percent compared to gas versions. BMW is fielding a full range of diesels, Mazda is offering a diesel A6, and Audi has clean diesel versions of the A3, A4 and Q7.

There are a number of diesel-powered pickup trucks available, including Ford, General Motors and Chrysler.

What do I need to do to run my car on veggie oil?

It's complex. There's a tank for regular diesel fuel, for starting the car, and a second tank for the vegetable oil. This second tank contains a metal coil that transfers heat from the engine's coolant (electric heaters are also used). The driver starts the car on diesel fuel, and can only switch over to vegetable oil when the veggie oil has warmed up enough. Before you turn the engine off, you have to switch back to regular diesel and run the vehicle long enough to purge the fuel lines and injectors of the vegetable oil. Otherwise, the lines will get clogged and it'll be a whole lot of work if you ever want to get your vehicle started again.

Some designs require an auxiliary pump to move the warmed coolant from the radiator to the tank of vegetable oil.

Is vegetable oil a certified fuel?

No. Put this stuff in your tank, and you are most definitely on your own. You will have other eco-pioneers with you, if that's any solace.

The E.P.A. has yet to certify vehicles to run on straight vegetable oil. Driving such a vehicle could, in theory, result in some hefty fines -- although the feds don't seem very interested in arresting anybody.

Is this something for the environmental fringe?

You bet.

If you find yourself with plenty of time on your hands, don't mind getting dirty modifying your vehicle, could care less if you void your car's warranty, don't mind skulking around the dumpsters of fast food joints, then straight vegetable oil might be for you. Many of us, though, would consider it a huge hassle -- with plenty of risks. There's a reason most converters work on older cars.

What's in it for me?

First, vegetable oil comes entirely as a renewable resource that's grown right here in the U.S. That reduces our dependence on foreign oil.

Vegetable oil also reduces most tailpipe emissions, including the amount of "air toxics" and soot released into the atmosphere, compared to regular diesel fuel. However, it actually increases the smog-making nitrous oxides, compared to regular diesel.

There's another downside, too. When you factor in the fossil fuel normally used to grow the plants used to make vegetable oil, the results are less encouraging. When the "lifecycle" of the fuel is considered, using pure vegetable oil actually increases the pollution to the atmosphere by about 35 percent.

Of course, if you're using vegetable oil that would normally be tossed in the dumpster, then you're definitely helping to save the planet.

What about global warming?

Using vegetable oil can help curb global warming. Unlike conventional petroleum, the carbon dioxide is part of a "closed cycle" that is reused by plants, before it's what? Made back into fuel again! So the only contribution of carbon dioxide is from the conventional fuel used to grow the plants that are made into vegetable oil. When that's factored in, vegetable oil fuel results in about a 75 percent reduction in greenhouse gasses, compared to regular diesel.

Would I have to be nuts to even consider doing this?

Straight vegetable oil is pretty far out there -- the folks who are doing this clearly relish being eco-pioneers, and not surprisingly some even tend to become a bit, um, obsessed, shall we say.

Will it hurt my car to run it on vegetable oil?

Straight vegetable oil is a better solvent than petrodiesel, and will probably result in clogged filters as old deposits on tank walls and pipes are loosened. Natural rubber gaskets and hoses in vehicles (mostly found in older vehicles manufactured before 1992, when high sulfur diesel was in use) will be degraded by vegetable oil, and will have to be replaced.

Will I get better mileage with vegetable oil?

Vegetable oil should give the same miles per gallon as petrodiesel.

What about my warranty?

When it comes to running vegetable oil through your vehicle, you can kiss your warranty goodbye! But what do you expect? Can you imagine what the dealership is going to say when they see the added-on plumbing, and a tank full of the stuff their lunch was fried in?

I'm thinking about getting a new car. Should I get a diesel that I can convert to run on vegetable oil?

We wouldn't.

Here's why. Current gasoline engines are far less polluting when compared to diesel vehicles, including diesels using the new, cleaner diesel fuel that's being introduced this year.

Because they're not many diesel vehicles, it's also harder to find a mechanic who will work on one.

We'd suggest you consider a fuel-efficient, conventional or hybrid gas vehicle.