I STILL remember learning from my father how to carefully remove a dipstick to check the oil level in our cars. It was drilled into me — along with turning off the lights when you left a room and clearing the plates off the table after dinner — that oil needs to be changed every 3,000 miles or so.

I’m not sure what I thought would happen if I didn’t, but I vaguely imagined an unlubricated engine grinding to a halt.

Childhood habits are hard to undo, and that’s often good. To this day, I hate seeing an empty room with the lights on.

But sometimes, we need to throw aside our parents’ good advice. In March, for example, I wrote about how we should relearn the dishwasher and laundry soap habits we inherited from our mothers.

Add frequent oil-changing to that list.

“There was a time when the 3,000 miles was a good guideline,” said Philip Reed, senior consumer advice editor for the car site Edmunds.com. “But it’s no longer true for any car bought in the last seven or eight years.”

Oil chemistry and engine technology have improved to the point that most cars can go several thousand more miles before changing the oil, Mr. Reed said. A better average, he said, would be 7,500 between oil changes, and sometimes up to 10,000 miles or more.

The California Integrated Waste Management Board ran public service announcements for several years about “the 3,000-mile myth,” urging drivers to wait longer between oil changes. Although the information is a few years old, the board has a list of cars on its Web site and how often they need oil changes. The concern is not only the cost to drivers, but the environmental impact of throwing away good oil, said Mark Oldfield, a recycling specialist for the agency.

But the situation is not that clear cut, according to Robert Sutherland, a Pennzoil scientist who works at Shell Global Solutions.

Rather than picking a number, Mr. Sutherland said, he recommends following what your owner’s manual advises. I checked the manual for our 2007 Mazda5 and had to determine if my typical driving included a lot of stop-and-go driving, short distances, extended idling, muddy, rough or dusty roads or really humid or cold temperatures.

Hmm. Yes, to short distance and stop and go. So that meant I should get the oil changed every 5,000 miles. If I did a great deal of longer-distance highway driving, it would be every 7,500.

The different types of driving are usually known as severe and mild (which is also sometimes called normal), Mr. Sutherland said, which seems counterintuitive since most of us probably don’t think we drive in severe conditions. But we do.

The reason, he said, is that if you take a trip of less than 10 miles or so, the engine and the oil are not completely warmed up. And if the oil is still cool, he said, it cannot absorb the contaminants that come from internal combustion as efficiently.

“It’s designed to work best when fully warmed up,” Mr. Sutherland said. “If you’re running to the music lesson, to school, the gym, that’s severe driving conditions.”

Mr. Sutherland said he has a mild commute. “It’s 47 miles, all highway.”

What actually happens if you don’t change your oil? Well, it doesn’t run out, it simply gets dirtier and dirtier. It’s like mopping the floor with a bucket of water and detergent. The water starts out clean, but the more you use it, the filthier it gets. Eventually, you’re making the floor dirtier if you don’t change the water.

Some people remain attached to the 3,000-mile oil change and have a hard time trusting the recommendations in the owner’s manual. If you’re one of those skeptics, you can send your engine oil out to be analyzed. Blackstone Laboratories in Fort Wayne, Ind., one of the best-known places for engine oil analysis, will send you a free kit.

You send back an oil sample and for $25, they’ll tell you all sorts of things about your car.

“We would compare what your oil looks like compared to the average Mazda5 of that year,” said Kristen Huff, a vice president at Blackstone. If there is a lot more lead in my oil than in a typical Mazda5, for example, it means I have a bearing problem, she said.

Her lab runs about 150 samples a day and a fair percentage of those are consumers looking to find out how often they need to change their oil, Ms. Huff said.

“Very often, it is the case that they’re changing their oil too often,” she said. “They do what their dad did with his ’55 Chevy.”

Another way to get a more accurate assessment of your oil needs is to buy a car that has a maintenance minder, like a Honda. A light on the dashboard alerts the driver when the system judges that the oil has only 15 percent of its useful life remaining. The time between oil changes varies depending on the driver and driving conditions.

Honda has used such maintenance minders on most models for at least the last five years, said Chris Martin, a Honda spokesman. Previously, the owner’s manual suggested changes every 10,000 miles in mild conditions and 5,000 miles in severe conditions.

Still, some people stick to the 3,000-mile changes, because “the Jiffy Lubes of the world have done a good job convincing people,” Mr. Martin said

It’s not just the fast oil change outlets. My sticker from my trusted mechanic states that I’ll need a change in 3,000 miles or three months. But Jiffy Lube, the largest quick oil change company in North America, is now under pressure to change its automatic 3,000-mile recommendation.

For about a year, the company has run a pilot program with some franchises across the country suggesting that instead of a blanket recommendation, mechanics tell customers what the manufacturer recommends under mild or severe driving conditions.

“By this time next year, every Jiffy Lube will do it,” said Rick Altizer, president of Jiffy Lube International. And the little sticker on your windshield will no longer simply state when the next oil change should occur, but, “I choose to change my oil” at a specific mileage.

“It’s so it’s not some arbitrary technician saying this,” Mr. Altizer said, but the consumer’s decision.

Mr. Reed of Edmunds.com said car owners often got conflicting messages because of an inherent tension: “The car manufacturers want the reputation that it makes cars that last a long time. The dealership wants to see you every three months.”

But he acknowledged that “3,000 miles strikes a deep chord with the consumer,” adding: “It feels good to get an oil change. If you fill up the car with gas, wash it and change the oil, it runs better. Of course, it doesn’t. But it’s the perception.”

Although Mr. Reed is doubtful that most drivers fall into the severe driving category and fears mechanics will use that to push drivers into paying for more oil changes than necessary, Mr. Sutherland said he wouldn’t want “to second-guess the manufacturer.” Vehicles, he said, “are a substantial investment and changing fluids is how you protect that investment.”

So before you go in for your oil change, dig out your owner’s manual and see what it says. And when the mechanic slaps on a sticker that gives the next change date in 3,000 miles, ask questions. And then, go get the car washed. That’s one thing that always seems to be needed.