Still, Wallace drives all over the area in his light blue 1978 Mercedes diesel. And recently he and his partner, Marj Ottenburg, drove to Fresno--that, too, without stopping for gas.

Wallace, a retired metallurgist, has been running his car on used cooking oil--and by all accounts, quite successfully.

The idea of using cooking oil first struck Wallace last year after reading newspaper and magazine articles about bio-diesel being used to power cars and trucks. A self-confessed "tinkerer" and experimenter, Wallace was so fascinated with the idea that he contacted people in Santa Cruz who sell bio-diesel to gain an understanding of how the whole process worked.

"Bio-diesel is cooking oil from which glycerin has been removed," says Wallace, a process that keeps the fuel from freezing. Since Wallace only drives locally and wasn't concerned with the problems associated with freezing temperatures, he determined that he didn't need bio-diesel--he was confident that he could run a car on used cooking oil.

"I could run it for free; I'm a cheapskate," says Wallace cheerfully.

It was the beginning of an experiment that was going to take up a lot of his time.

To begin the process, Wallace had to find a diesel car. Being the self-proclaimed "cheapskate" that he is, he wanted one that wouldn't cost much. Wallace attended a car auction on King Road in San Jose, where he met Mark Shapiro, a collector of old diesels.

"I helped him find a good diesel," says Shapiro. "He sounded like an inventor; he also sounded like someone with a lot of time on his hands."

Wallace spent $2,000 and drove home in a Mercedes.

His next step was to convince restaurant owners to let him have some of their used cooking oil. He found one in Saratoga and another in Cupertino.

Wallace began his experiment by pouring a small amount of the used cooking oil into his fuel tank, mixing it with the diesel already there. There was no noticeable difference in the car's performance.

But used cooking oil is filled with impurities and sediments and Wallace was afraid that they would clog up his engine.

So Wallace set to work in his garage, a workshop cluttered with materials from his earlier experiments.

He tried to use bed sheets as filters, but they created a huge mess. "My dogs licked up the excess oil," he says.

Then he tried to use the paper bags used in vacuum cleaners. But they cost $2 apiece, and Wallace was having nothing of that.

Wallace found an easier solution. "I just let the oil settle down. The sediment collected at the bottom. I slowly poured the oil into another container," he says.

But he still had problems with the car's fuel filter.

On the trip to Fresno, the car sputtered to a halt because the filters were clogged. "It took me about three minutes to clean the filter and then we were on our way again," Wallace says.

He now uses a more extensive sedimentation process that takes a week before he can use the fuel.

Wallace loves showing off his new car to visitors and explaining "the whole enchilada," as he calls it.

A ride in the cooking oil car is no different from a regular car except that the car smells like a kitchen or of deep-fried food.

"It sure beats the smell of burning diesel," says Shapiro.

Wallace has also rigged up an improvised viscometer that tells him about the mix of cooking oil and diesel that he has in the car. "When I first bought the car, the fuel tank had diesel in it. I've been adding cooking oil ever since. I am up to 95 percent cooking oil now," he says.

Ottenburg has been used to Wallace's ways for quite a while. "If he makes a mess in the garage, he'll have to clean it up," she says. "But it keeps him occupied. He is a creative thinker. It's enjoyable to watch him."

She says that Wallace's mind is always churning.

Two decades ago, he started to manufacture snow shoes after Ottenburg slipped and injured herself on a trip to the Sierras. The shoes, called Polar Paws, would not slip sideways.

"The Polar Paw had teeth all around. It never slipped sideways," says Ottenburg. Wallace supplied the shoes to the U.S. Marine Corps for a while, but demand waned and the market soon dried out.

"We still have a stack of partly-made snow shoes in the garage. I think those shoes were ahead of their time," says Ottenburg.

Wallace's next venture was a water purifying kit for backpackers.

He had read about two doctors in Los Angeles who had contracted stomach infections after drinking contaminated water during a backpacking trip.

Wallace had a solution--Polar Pure, a little glass bottle with iodine in it that would purify the water. REI sells Polar Pure through its outlets. Other stores catering to the backpacking community have also sold Polar Pure over the years. Once in a while, Wallace still gets bulk orders for the product from backpackers across the country.

"He's always mulling over something productive, or he would go stir-crazy," says Ottenburg. "Or maybe he is stir-crazy right now."

Don Irving, an electronics engineer who lives in Saratoga, has known Wallace for more than two decades.

"He is the sort of guy who can go in cold into a bar or restaurant and have everyone talking to him in a little while," he says. "He loves to get his hands on something. He is always trying something new."

Irving says that Wallace is knowledgeable in a lot of areas and is quite obsessed about mechanical things.

That's what drove Wallace to the subject of bio-diesel in the first place. Ray Kemp was one of the first people he contacted to understand the use of the fuel to run cars.

Kemp has been selling bio-diesel in Santa Cruz for the last 15 months.

Wallace persuaded Kemp to speak about bio-diesel at a Sierra Club meeting at the Saratoga Library. At the same meeting, Wallace gave a demonstration of his cooking-oil car.

"He is an independent-minded experimenter. He doesn't bow to conventional wisdom," says Kemp.

Even so, Kemp is not a big fan of using cooking oil to run cars.

"It's going to fail eventually. It's going to clog the filters and burn off the tips of the fuel injectors," he says. "It will work fine for 10,000 miles or so. But it might also cause premature engine burn."

Kemp suggested that one way of avoiding the problem would be to use a contraption called the SBO converter.

"In that system, the car runs partly on cooking oil and partly on diesel. There are two separate fuel tanks. The engine starts on diesel, switches to cooking oil and then switches back to diesel before the engine is switched off," Kemp says.

Wallace says that since he is old and does not drive a lot, the used cooking oil is going to work just fine for his car.

"When you get old, you don't have to go anywhere," says Wallace. "And this is purely experimental."

Wallace has now started frequenting discussions and conferences about alternative fuel sources. He talks proudly about his cooking-oil car wherever he goes. "A bunch of UC-Santa Cruz kids called me and asked me to go give a talk," says Wallace.

Wallace is sure to tell them what he tells everyone else. "This is good for the environment," he says. "They could use it to run boats. Even if there is an oil spill, cooking oil is edible. The fish could eat it."

Wallace says sooner or later the planet's stock of fossil fuels is going to run out. "We might not have any gasoline in 40 years," he says. "If I am still around, I'll still be driving my car using cooking oil. We'll always have restaurants."