Courtesy of Goodyear

Craig Henderson of Bellingham, Wash., which is about 90 miles north of Seattle, planned to drive his home-built car from the Canadian border to Mexico without stopping for fuel. Before leaving on Aug. 29, he’d carefully calculated that his streamlined car could travel the more than 1,400 miles on 14 gallons of diesel.

Of course, things didn’t go exactly as planned. By the time Mr. Henderson arrived at the border at Tijuana three days later, the bright-red coupe, called the Avion, had used only 12.4 gallons of fuel, for an average of 119.1 miles per gallon.

“I could have driven halfway back,” Mr. Henderson said in a telephone interview.

“I’m very, very happy,” he said, sounding breathless but relieved. “We proved it’s not a fluke. We didn’t just break our old record, we smashed it.” The Avion earned a place in the Guinness Book of World Records in 1986 during a similar drive from Canada to Mexico at an average 103.7 miles per gallon.

Designed and built by Mr. Henderson and his friend and fellow engineer Bill Green, the Avion – French for airplane – has a fiberglass exterior and gullwing-style doors that swing up and out from the body. There is room for only two adults. A 3-cylinder diesel engine from a Smart Fortwo is mounted behind the passenger compartment. Power is delivered to the rear wheels using a 6-speed semi-automatic transmission.

During this most recent trip, driven in a nearly straight line south along Interstate 5, the Avion had no trouble beating its old record. The total driving time was 29 hours 28 minutes. Stops were made for food and rest, but never fuel. “People gave lots of thumbs-up and cellphones were out snapping pictures,” Mr. Henderson said. The only hiccup came almost within sight of the finish, during a grueling traffic jam in San Diego. “I was thinking, this won’t work if I crash,” Mr. Henderson said.

Two years ago he drove the car, a slightly updated version (he enlarged the gas tank from 10 gallons to 17) of the original Avion, at an average of 113.1 miles per gallon from the Canadian border to the Oregon line. But with corporate sponsorship from Goodyear that got him new tires, Mr. Henderson’s ambitions expanded to a run along the length of the West Coast. “It’s great to get a sponsor to help do this,” he said.

Mr. Henderson says work has already begun on a second Avion.