If people could poke around Villa Montona, the 27-acre estate of the 75-year-old racing great, they’d be impressed. In addition to the Lamborghini in the garage, there’s a stockpile of trophies, plaques, and other mementos that sit three deep in display cases on the first floor. Most are from Andretti’s racing career, which spanned five decades and included 111 wins and four IndyCar series championships. But others, like his designation as a Living Legend by the Library of Congress, are also a testament to his post-racing life as an eclectic entrepreneur and investor—one who earns much more today than he ever did behind the wheel.

Being surrounded by souvenirs lets Andretti do something he did not do when he won them—savor his achievements. “Back then I just focused on work,” says Andretti. “Nothing was going to stand in my way.” He inherited this determined streak from his father, a farm administrator bent on ensuring a brighter future for his family after World War II. The family’s hometown, Montona, Italy, was annexed by Yugoslavia after the war (it’s now part of Croatia). After seven years in an Italian refugee camp, the Andretti family arrived in Nazareth in 1955 with $125.

Mario was then just 15. Three days into their American life, he and his twin brother, Aldo, got their first glimpse of dirt-track racing, at Nazareth Speedway. Four years later they were building stock cars, and Mario was passing himself off as a 21-year-old so he could score a racing license.

Andretti started racing professionally in 1964—in stock cars, sports cars, and single-seaters—and found triumph at every turn. In winning the 1967 Daytona 500, the ’69 Indianapolis 500, and the ’78 Formula 1 championship, he became the first to complete the rarest trifecta in racing. What drove him was a desire to provide for his three children and his wife, Dee Ann Andretti, a Nazareth native. (They’ve now been married for 53 years.) “I was lucky to have a woman who really supported me,” Andretti says. “She probably would’ve liked to have picnics and Fourth of July barbecues. But I’m working on all the holidays, all the Sundays.”

Many fans were surprised that Andretti kept racing into his fifties, but the idea of retirement spooked him. When he did decide to hang up his fire suit in 1993, at 53, it was with the ’94 season—his Arrivederci Tour—still to race. “I really didn’t have a plan,” he says. He did have money; he had earned more than $11 million on the track and also got paid for licensing deals, speaking engagements, and endorsements. But that wouldn’t be enough to finance the racing endeavors of Andretti’s sons, Michael and Jeff, and his nephew John, and living off savings wouldn’t satisfy his own high-revving spirit.

Adjusting to a slower pace, Andretti began to leverage some of his assets: a name synonymous with speed and experience marketing it. Andretti’s business manager, John Caponigro, a former legal counsel to the CART racing series, encouraged him to parlay his corporate affiliations into something more lasting. To that end, in 1997 Andretti partnered with M.J. Castelo, a former Texaco marketing executive, to create Andretti Petroleum, intending to build it into a wholesale fuel distributor and chain retailer.

Today that company, along with related entities, owns 37 gas stations in California. Andretti talks with Castelo several times a week about everything from front-end planning to closing deals. “He’s got a great seat-of-the-pants feel for business and a pretty uncanny knack of being able to work with and read people,” says Castelo. While Andretti Petroleum declined to provide revenue figures, Andretti says the business is his family’s biggest source of income and “probably the best thing that could have happened to us as far as stability.”

Andretti’s true off-road passion, however, is wine. A regular visitor to Napa Valley, he had befriended winemakers who invariably cautioned him against risking money in such a fickle game. But an Andretti wine sold through a licensing deal in 1994 was so successful that the following year he and Joe Antonini (the CEO of Kmart (SHLD), a longtime racing benefactor) bought a distressed Napa vineyard. “It was a weak moment in my life,” Andretti says now, sarcastically.

After considerable investment to overhaul the vines and the staff, the Andretti Winery opened in 1996. It now distributes 30,000 cases a year across 30 states. As a business it holds its own, Caponigro says, but Andretti sees it as a labor of love, not a meal ticket: “I don’t want it to get any bigger.”

Wine and fuel provide just two of Andretti’s revenue streams. He still does a range of endorsements and earns money driving, via the Andretti Experience, a white-knuckle ride-along that he gives to fans at IndyCar races in a specially made two-seater. In other words, he’s nowhere near ready to idle around his house. “I can definitely say I’m still living the dream,” he says. 

A version of this article appears in the June 15, 2015 issue of Fortune magazine with the headline ‘A Racing Champ’s High-Octane Encore.’