Car Talk's Guide to Alternative Fuels


What is biodiesel? It's a mix of modified vegetable oils (that's the "bio" part) and conventional diesel fuel. In 2011, more than a billion gallons of biodiesel were produced in the U.S. There are 205 EPA-registered plants, with annual capacity of more than three billion gallons. The market for biofuels remains relatively small but growing, and it supplies about one percent of the world's transportation fuel.

A joint study by Departments of Energy and Agriculture estimated that advanced biofuels could provide 37 percent of our transportation fuel in the next 20 years. It even said that biofuels could be 75 percent if cars and trucks doubled their fuel economy—which is what auto manufacturers basically have to do with the federal fuel economy regulations that require cars to reach 54.5 mpg by 2025.

How is biodiesel sold?

Biodiesel is usually sold in ratios of 10- or 20-percent modified vegetable oil and 80- or 90-percent conventional diesel. These fuels are called B10 or B20. The B factor tells you the percentage of modified vegetable oil. In other words, B100 is pure modified vegetable oil, while B20 (a popular fleet fuel) is 20 percent modified vegetable oil and 80 percent regular diesel.

Soybean oil is usually the raw material in the vegetable part of the fuel, but rapeseed oil and animal fats can be used, too. Experiments with Vitalis, Cheese Whiz and Soy Pez remain inconclusive.

Will I have to modify my diesel vehicle to use biodiesel?

Not if you use fuels with a relatively small percentage of vegetable oil, such as B10 or B20. These fuels can be used in a regular diesel vehicle without any special concerns. One minor note is that biodiesel is a solvent, so when used initially it might loosen deposits and clog your fuel filter. Check that filter regularly and you should be fine.

Where do I get it?

Biodiesel is sold commercially.

At the present, there are more than 1,800 public locations in the U.S. that sell biodiesel. That number is going up, but it's still infinitesimally small, compared to the estimated 160,000 gas stations in the country. You can also purchase biodiesel in 55-gallon drums, delivered right to your door. (Really want some? Check out our resources area.)

So, it's an official, government-certified fuel? I'm not going to get arrested, and Officer Obie won't take 8x10 color glossy photos if I use biodiesel?

You're safe.

Biodiesel has passed the health effects testing requirements of the Federal Clean Air Act, and is certified for inclusion under the Renewable Fuels Standard (RFS-2), which mandates production of 36 billion gallons of renewable fuel by 2022. Biodiesel also has the seal of approval from the very powerful California Air Resources Board.

Is biodiesel for the wacko, environmental fringe?

Let's just say that it takes a certain amount of commitment to pour B100, or straight vegetable oil, into that diesel engine. Commitment isn't usually a problem with wackos.

Anything up to B20 can go right in your diesel engine's tank, though there's more concern with 2007 cars up because of their use of advanced pollution fighters such as diesel particulate filters, oxidation catalysts and (on some cars) Selective Catalytic Reduction catalytic converters, because they're very susceptible to contamination. One solution would be running newer cars on B5 or regular diesel fuel until the warranty expires, then switching to B20. Anything above that, you're on your own, though some people say their vehicles run just fine on even B100.

And, while it may not score you a date with the guy with a bird's nest in his beard, it strikes us as a lot less hassle than trying to fuel your car with straight vegetable oil.

What's in it for me if I switch to biodiesel?

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

Biodiesel reduces a number of tailpipe emissions, including the amount of "air toxics" and soot released into the atmosphere, compared to regular diesel fuel. But biodiesel actually increases the smog-creating nitrous oxides. There are a few other disadvantages to biodiesel, too, though they are lessened by the introduction of ultra-low-sulfur diesel fuel in the U.S. B100 delivers 10 percent less power than regular petroleum diesel, the E.P.A. and D.O.E. say, and it's not great in very cold places.

On the upside, did we mention that it's biodegradable and a domestically produced fuel?

What about global warming?

Biodiesel can help curb global warming. A joint study from the Departments of Energy and Agriculture said that biodiesel reduces net carbon dioxide emissions by 78 percent compared to petroleum diesel. Unlike conventional petroleum, the percentage of biodiesel that's from plant matter is part of a "closed cycle”; that is, reused by plants before it's what? Made back into fuel again!

Even if you run B20, you still get a 15-percent reduction in greenhouse gases compared to conventional diesel.

How can I modify my Honda Civic to run on biodiesel?

You can't. You need to start with a diesel-powered vehicle. There's been talk of a diesel Accord for the U.S., but it's not happening soon. The good news is that the range of diesel vehicles available from Mercedes, BMW, Audi, Jeep, Mazda and many other companies keeps growing.

Will any diesel vehicle run on biodiesel?

Yes. Except, of course, diesels that won't start with conventional diesel. They will continue to sit in the pasture and rust. The good news is that diesels tend to be extremely reliable, a fact made irrefutable by the sheer number of million-mile-plus diesel vehicles on the road today.

A diesel? Didn't they stop selling those in the U.S.?

They nearly did, after some terrible diesel vehicles in the ‘70s and ‘80s. Does anybody remember the ill-fated Oldsmobile diesels, which barely made it out of showrooms before breaking down? It didn't help that their power plant was based on and used many components from the Rocket V-8 (a typical corporate, bean counter maneuver!), and the engine as designed couldn't handle a diesel's high compression ratio.

For a while, Mercedes, Volkswagen and Jeep were the only companies producing diesels, but that's no longer the case. GM buyers have a much better choice than those awful Oldsmobiles—a diesel Cruze. Also producing diesels for America are BMW, Audi and Mazda. Truck buyers have always had diesel options, because it's such an economical choice.

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

Biodiesel is becoming more widely accepted -- so much so that even politicians (our leaders) are starting to follow.

Will it hurt my car to run it on biodiesel?

A mix of 10- to 20-percent vegetable oil to diesel (B10 or B20) seems to be quite safe, though many manufacturers only warrant the use of B5. Some pioneers, who blog about their fuel use and mung bean gardens, say they've been running on B50 with no problems to date, and trucking fleets like that of British supermarket giant Tesco have tested it. Some report good results, but we don't have enough evidence to endorse that yet.

Using B100 is another story. Though it doesn't introduce nearly as many hassles as using straight vegetable oil, B100 may require replacing some fuel line components, and can result in some operating problems -- especially in cold weather.

Will I get better mileage with biodiesel?

You should get about the same miles per gallon on B20 as 100-percent petrodiesel, though you might experience a small (one- or two percent) mpg loss. With B100, the mileage loss would ratchet up to five- or ten-percent.

What about my warranty?

B10 and B20 are approved, federally regulated diesel fuels. That said, many automakers say their cars are certified only for blends up to B5, and some claim that using B20 and higher will void the warranty. But the Northwest Biofuels Association and Oregon Auto Dealers Association claim that voiding a car's warranty based on the fuel it uses violates the Magnuson Moss Warranty Act of 1975. It's a bit of a gray area that could use some clarification. We haven't heard of a huge problem with voided warranties, though.

Where can I buy biodiesel?

The NBB website has a map showing all the biodiesel retail locations in the U.S. Not surprisingly, these are concentrated in the Midwest, home of the soybean, but both coasts are also fairly well represented.

I want to make my own biodiesel! What's involved?

A lot of work, actually. Reprocessing plutonium might be easier. You need some containers, pure methanol, lye, a scale accurate to 0.1 grams, duct tape, a thermometer, funnels, a blender and some measuring beakers. An advanced chemistry degree might be helpful. Some folks are going all the way, planting their own rapeseed and pressing their own vegetable oil.

Before you go tilling the front yard, though, you might want to know that you'll need at least an acre of rapeseed to produce 100 gallons of oil for fuel. Don't forget, too, that you'll need some sort of an additive to keep your biodiesel from going rancid. Happy farming!

I'm thinking about getting a new car. Should I get a diesel?

We would have said definitely no a few years ago, but today's diesels combine really great mileage with hugely improved environmental performance, thanks to the ultra-low-sulfur fuel that's now the only kind of diesel you can buy. It's 97 percent cleaner than the conventional diesel it replaced.

There are still some disadvantages to diesels, including the higher cost of the fuel and more challenges finding a good mechanic. We wouldn't discourage you from looking at diesels, but we'd also suggest you consider a fuel-efficient conventional car, a hybrid or plug-in hybrid, or even a battery electric. They're all eco-champs, too.