When Brian Maupin cranks the ignition in his Ford F-250, the diesel engine roars to life. But anyone standing behind this mammoth of a truck will be surprised to find that the exhaust smells nothing like petroleum. Oddly enough, the pick-up exudes an odor that resembles…”French fries,” Maupin fills in the blank.

That’s because his truck doesn’t run on diesel. It runs on vegetable oil. And better yet, used vegetable oil that he gets free of charge from a neighborhood burger joint. All it costs Maupin is a trip to Curly’s once a week to pick up a couple 35-pound jugs of the stuff.

It doesn’t hurt that vegetable oil emissions are atmosphere-friendly. But don’t be too quick to lump Maupin with the bleeding heart, save-the-earth types.

“I’m not really a tree hugger; I’ve never been a liberal or an environmentalist or anything,” he professes. “I’m really a businessman.”

Maupin stumbled across the concept of vegetable oil fuel last summer, when climbing gas prices made him reassess his 14-miles-per-gallon Yukon, especially considering his 50-miles-a-day commute to Frisco and back. He thought about getting a hybrid, but owning three neighborhood rental properties often requires him to act as handyman.

“You can’t throw two-by-fours in the back of a Prius,” Maupin reasons.

Another option was a truck that runs compressed natural gas (CNG), a cheaper and cleaner alternative to gasoline. The City of Dallas leads the nation with 1,200 municipal vehicles running on CNG, and 14 fueling stations are scattered throughout Dallas and its surrounding areas. But trips beyond Dallas would have been out of the question, plus Maupin was more concerned about saving money than saving the earth.

That’s why used vegetable oil appealed to him – no price per gallon. He ordered the fuel converter kit and bought the F-250, only later striking up an agreement with Curly’s owner Luan Vraniqi.

“I knew it could come back to bite me. I didn’t tell anybody at first because it felt kooky for a while,” he admits. “There wasn’t a single person I knew that was doing it.”

Maupin opted to spring for the most expensive fuel converter kit – the $3,500 one with the 100-gallon custom-made aluminum tank. He could have turned veggie oil into fuel for as little as $800, but this way, if both the tank sitting in his truck bed and his diesel tank are full, he can take a 2,200-mile roundtrip.

“I can drive to Disney World and back without ever stopping to fill up,” Maupin boasts of his 18-mpg truck. (That’s with either diesel or veggie oil.)

Here’s how it works: Maupin starts his engine on diesel fuel and lets it idle a couple of minutes while the converter kit heats the vegetable oil to a temperature of 158 degrees, thinning it to the same consistency as diesel. Then Maupin flips a switch on his dash, which feeds vegetable oil to the combustion chamber to burn the fuel. When he parks, he idles the engine for another couple of minutes while the converter kit purges the vegetable oil from the injection pump and injectors.

This process works only with diesel engines because they compress air to create high temperatures instead of using sparkplug or ignition systems. The vegetable oil doesn’t hurt the truck a bit, Maupin says. It acts as a lubricant, and everything Maupin reads makes him believe that it should extend the life of his truck longer than petroleum diesel would. Plus, he figures he saves $180 to $200 a month in gas.

“In theory this truck will start paying me in about five years – a far cry from the typical model of depreciation,” Maupin says. “You usually lose about $1,000 a year on a vehicle, plus the price of gas.”

Curly’s decided to make the switch, too – to trans fat-free oil. Maupin was having trouble using the restaurant’s partially hydrogenated oil last winter because it gelled quicker than pure oil, so Vraniqi started using the healthier stuff in his fryers, for both his customers’ and Maupin’s sake.

“It’s a little more expensive, but it sends a good message,” Vraniqi says. “One customer commented that it has a crisper, cleaner taste.”

Maupin encourages others to make the switch as well. It does take a little sacrifice – you have to be willing to give up the convenience of pulling up to a pump and swiping a credit card to refuel (though at least two stations in Dallas now pump straight vegetable oil for roughly $2.45 a gallon). But the benefits are worth it, Maupin says. In fact, he views it as a patriotic responsibility. Europe latched onto this technology 20 years ago, but Americans are still dependent on oil and, thereby, “countries that don’t like us,” he says.

“We’re consumer-based. The consumer has to demand it before the companies start pushing it,” he says. “The solution for America is to be a combination of all these alternative fuels.”

He hasn’t convinced everyone. People still give Maupin a hard time, smirking and calling his truck the “French fry-mobile,” but it doesn’t faze him.

“That’s always good for a laugh,” Maupin says, “and then ultimately they get a little jealous and wish they could do the same.”