The expression "fill it up with regular" disappeared with the dawning of 1992 from the Golden State's roadside lexicon.

California is the first state in the nation to ban leaded gasoline, the final step in a 20-year effort to rid the environment of the toxic metal, which impairs children's mental and physical development."It's the end of an era. The older cars are going to diminish on the roads," said Bob MacMillan, master technician at the National Automobile Museum in Reno, Nev. "You've got to decide if you're going to bring up your car to use unleaded or park it for a showpiece."

In California, about 1.5 million of the 22 million cars on the road use leaded gas. Drivers searching for the right fuel are getting conflicting advice from the state, mechanics and antique car collectors.

Some, including the state, which passed the new rules, say old cars will run fine on unleaded with no changes. Others recommend using special additives with unleaded gas or spending about $700 to replace or recondition old cylinder heads.

California Air Resources Board spokesman Jerry Martin is assuring consumers that the refiners have perfected new unleaded gasoline formulations that contain additives.

"The additives are already in the gas; the car will work fine," Martin said.

"A lot of people who were using regular really didn't have to," said Mitch Rudoni, assistant service manager at Ron Price Motors in South San Francisco. He recommends medium-octane unleaded. "If you're getting a pinging, you should go to the higher octane."

About 1971, manufacturers started building cars with bronze-silicon or harder valve guides for the inevitable removal of unleaded from the market.

Leaded gas does two things: It increases octane by slowing the fuel-burning rate, and it coats the valve guides, like the lubricant graphite, to reduce friction and heat that erode the valve guides and surfaces.

"Those changing from leaded to unleaded will have to make changes if they want to keep their own old cars," said MacMillan.

Distributed by Scripps Howard News Service