Andy Granatelli, a colorful entrepreneur who turned STP oil treatment into a national institution and built racecars that won the Indianapolis 500 in 1969 and in 1973, died on Sunday in Santa Barbara, Calif. He was 90.

The cause was congestive heart failure, his son Vince told The Associated Press.

In 1961, the Studebaker Packard Corporation acquired Chemical Compounds, a company with seven employees and only one product: STP (for scientifically treated petroleum). Mr. Granatelli was named the president and changed the company name to STP.

Within a decade, the company had 2,000 employees and was selling more than 100 million cans a year, and its annual sales of

$2 million had grown to $100 million. STP decals, with the slogan “The Racer’s Edge,” were everywhere, both at racetracks and on the bumpers of family station wagons. Mr. Granatelli appeared in commercials for the product.

But in 1971, an article in Consumer Reports said STP oil treatment was actually “thick goo,” a worthless oil thickener. Mr. Granatelli denied that, but stock trading halted, and in two days, the stock, which had been at $58, fell to $38.