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

Pretty much — with two big caveats. First, it needs to be diesel-powered to begin with. Second, vegetable oil tends to congeal when the weather gets cool, which means you'll need to undertake some major modifications.

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.

A diesel? Didn't they stop selling those in the US?

Mercedes, Volkswagen and Jeep are the primary suppliers of new diesel passenger vehicles in the US, although not all states allow the sale of new diesel vehicles, due to the pollution they contribute.

There are a number of diesel-powered pick-up 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. 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 must 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 may also 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 EPA 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 disposed to clap anyone in irons just yet.

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.

What's in it for me?

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

Vegetable oil also reduces most tailpipe emissions, but actually increases the smog-increasing nitrous oxides compared to regular diesel.

However, 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%.

On the upside, vegetable oil does reduce the amount of "air toxics" and soot released into the atmosphere, compared to regular diesel fuel.

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% 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 much less common, it's also harder to find a mechanic who will work on a diesel vehicle.

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