7 On Your Side: State officials say drivers may be wasting money on unnecessary oil changes

SAN FRANCISCO (KGO) -- It's one of the most controversial questions in car care - when to change your motor oil. There's a lot of conflicting information and state officials say millions of dollars are being wasted on unnecessary oil changes. 7 On Your Side's Michael Finney sorted it out for you.

So which do you follow - the little sticker the mechanic puts on your windshield or the manual that comes with your car? They don't always say the same thing.

Now a state legislator wants to make sure they do.

7 On Your Side asked three different auto shops how often you really need to change your oil and got three different answers, all for the same model Ford Fiestas.

Serramonte Ford in Colma said every 10,000 miles.

A Jiffy Lube in San Francisco gave 7 On Your Side a receipt that said 5,000 miles.

In Concord, at Oil Changers 3000, the mechanic told our producer 3,000 to 4,000 miles.

"There is a lot of confusion out there and what's happening is consumers are responding to kind of that lowest common denominator information," said Californians Against Waste spokesperson Mark Murray.

It used to be clear cut - change your oil every three months or 3,000 miles.

"It's still stuck in people's heads. It's totally unnecessary," said Senator Ben Allen, D-Santa Monica.

Allen says that advice has been out of date for years. Car makers' recommendations now vary by the type of car, type of oil, and how you drive.

"The technology is much more sophisticated," he said. "In fact, some of them are now recommending 10,000-mile, even 15,000-mile oil changes."

Those guidelines are in your owner's manual, but several mechanics said most people never look and rely instead on what their auto shop says.

At Oil Changers 3000, the company president said there's so much confusion that they no longer put a return schedule on their windshield stickers.

But if a customer asks for the manufacturers' recommendation, they will provide it.

Now Allen is proposing a new law that would require auto shops tell customers the manufacturers' recommendation every time.

"And then, of course, if a driver has a particular set of special driving conditions or needs or they ask to have the interval be at 3,000 miles, that's fine," Allen said.

The nonprofit Californians Against Waste says the law would be a big win for consumers.

"They are going to spend less money on oil changes and it's going to be better for the environment because we are not disposing of so much motor oil," Murray said.

Some auto shop owners oppose the bill. One said people might wait too long to change their oil and void their warranty. The California New Car Dealers Association wants to make sure the same rules apply to all types of oil changing businesses.

Mechanic Paul Cowden said he's happy to tell customers what the manufacturer says but wants to keep some flexibility.

"In the city here, we drive a lot of very short distance trips and we probably should change our oil a little more often," he said.

Cowden believes virtually every car can go at least 5,000 miles between oil changes.

He says he tells customers that but he's still using a 25-year-old machine to print windshield stickers.

"It automatically adds three months and 3,000 miles," he said.

He tried handwriting longer intervals but the ink faded, so when he went back to using the machine. After 7 On Your Side's visit, he's considering buying a new one.

"It was not really an issue until today and I will look into it," Cowden said.

For now, the bottom line is to look at your owner's manual and, in newer cars, pay attention to warning lights that tell you when you need service.

If you've lost the manual, the state has a great online tool to help you find the manufacturers' recommendation for your car. Click here to see the online tool.

Written and produced by Jennifer Olney