They hit bottom at the side of an interstate in Indiana, after the big green bus faltered to a stop, engine coughing and sputtering. "I think this is it," Luke Scruby said, and then they felt one last wrenching shudder. They didn't need to see the smoke coming from under the hood, the shards of metal in the oil, to know it was all over.

Scruby, a fourth-year student at the University of Virginia, his older sister Emily and their friend Scott Wilcox had a three-way hug at the side of the road, just as the tow-truck driver pulled up, looking at them like they were crazy.

They were trying to get to Alaska in an old school bus converted to run on vegetable oil, stopping at fast-food joints all along the way to beg for used grease to fuel their trip, and promoting alternative fuels to anyone who would listen.

"Scott's a biofuel evangelist," Luke Scruby said.

So they weren't about to let a dead bus stop them.

Like many college students, they're pushing change from the fringes. With interest rising in biodiesel -- nationwide sales went from a half-million gallons in 1999 to more than 25 million last year -- many colleges are experimenting with alternative fuels. U-Va. has a pilot program running buses on biodiesel; James Madison University has a reactor to transform waste oil from campus dining halls into biodiesel.

The experiments are driven by rising gas prices, worry about dependence on foreign oil, environmental concerns -- and all those idealistic students clamoring for change.

Wilcox, an agriculture major who heads an environmental awareness group at Auburn University, and Luke Scruby, a mechanical engineering major, want to run an alternative-fuel company. "It just makes so much sense," Wilcox said.

So they dreamed up the trip. They had goals, they had principles, they had a message to spread. Besides, it's Luke Scruby's last free summer; he is in the Reserve Officer Training Corps, so he'll have Navy commitments next year.

In January, they bought a 1985 school bus, and Luke Scruby hooked up fuel tanks and hoses and filters so it would start with diesel, warm up, then switch to clean vegetable oil. Every weekend, for months, he worked on the mechanics. Wilcox worked on the interior, adding an old plaid sofa, cleaning up 20 years of gum wads shoved down between the seat cushions, wiring up an MP3 player and speakers.

They added 8-inch-high yellow letters outside, proclaiming "POWERED BY VEGETABLE OIL," and they named it Doris Cooper. It just kind of looked like a Doris, since it was an elderly bus, and Wilcox said it handled like a Mini Cooper.

Waste vegetable oil is the cheap, messy, out-there cousin to biodiesel, which is fuel made from plant or animal fats and often combined with petroleum-based diesel. Both are more environmentally friendly than petroleum diesel, but raw vegetable oil is much more of a hassle, in part because it needs to be heated initially (it can get too thick to run properly if it's cold). It can gum up the works of a car over time, some warn -- and forget the warranty. There's a growing industry converting used grease into biodiesel, which doesn't require changes to the engine.

Not Just Any Grease Will Do

The group set off in late May from the foothills near Charlottesville and headed west, wafting hush-puppy smells out the exhaust pipes.

Every 1,400 miles or so, they stopped at a restaurant to refuel. First they would peek in the grease bin out back, because if it was really dirty oil, with meat scraps and who knows what floating in it, it would clog everything up. If it looked good, they changed clothes -- they were worried about heading into Alaskan bear country smelling like french fries -- and pushed Emily Scruby in front.

"The boys would say, 'You ask. You're the cutest,' " she said. "So I would put a smile on my face, ask for the manager, and say, 'I have a peculiar request . . . ' "

Some restaurant managers laughed. Some refused. Some shrugged and pointed to the grease. Some got excited, asked a million questions, climbed into the bus, gave them free meals.

The three don't get real hungry for fried food anymore.

"Being out back by the Dumpsters with your head in a grease bin on an 85-degree day is a little less than super pleasant," Emily Scruby said. And there were some dead animals, squirrels and rats and things, that had gotten into the grease and drowned. Sometimes the pump would act up and spray oil all over them.

"It's not really glamorous," she said, "sucking grease like that."

But being in the bus was heady stuff. People stared, honked and waved. They listened to bluegrass, played cards, befriended strangers, gave tours of the bus's innards.

Now they've got friends saying they're going to convert their cars, too. Even Tim Scruby, Luke and Emily's father, is thinking about it. Wilcox dreams of setting up a fueling station at Auburn with used vegetable oil and biodiesel pumps.

As the trip continued, there were ominous signs. The bus broke down in Missouri. Then it slowed. And when it finally collapsed June 10, they couldn't tell whether the problem was the grease or just the 1,114,000 weary miles on the bus.

"This is a huge bummer," Luke Scruby said that afternoon by cell phone, riding backward in the bus as they were towed to a safer spot. His sister cried a little.

He was the one who first said they might have to scrap it. Wilcox hated the idea. But Emily Scruby, who graduated from Virginia Tech last year and is on her own now, with a job at an engineering company and bills to pay, was running out of money. It would cost more than $2,000 to tow it home.

Another Spark of Inspiration

They spent one last night in the bus in a scrap yard in a creepy neighborhood of Indianapolis, sharing beers with their tow-truck driver. The next morning, they tore everything they could out of the bus, loaded up a U-Haul and said goodbye.

"Doris was an old girl," Luke Scruby said. "Maybe it was her time to go."

He paused. "But we still want to have our vegetable oil crusade."

So back in Afton, in the Virginia countryside near the Shenandoahs where he and his sister grew up, Luke Scruby went to work on the navy 1976 Mercedes his great uncle gave him. It had been running on vegetable oil for a while, but he needed to prepare it for a long road trip. He spent long, hot days under the hood, and the trunk is now full of what they call Frankenstein, a soldered, bolted, grease-filtering monster.

Last weekend, he and Wilcox packed what used to be the back seat of the Mercedes with just the essentials -- a spare tire, a few clothes, hiking backpacks, fly-fishing rods, a guitar and a washboard so Wilcox could play bluegrass along the way. They rolled out through the folds of green hills past picket fences and horses grazing, took the Mercedes to a Mexican restaurant near home, pumped up a bellyful of grease and headed for the open road.

College students Scott Wilcox, left, and Luke Scruby have retrofitted a Mercedes-Benz to make it run on used vegetable oil. The stages of used vegetable oil: At left, from a restaurant; at center, partially filtered; and at right, ready for use as a more environmentally friendly fuel.