Top 7 Urban Legends About Motor Oil

What's True and False About How We Use Oil in Our Cars?


  • Mechanic Picture

    Mechanic Picture

    Many auto shops use the myth of the 3,000-mile oil change to get you in the service bay more often. | July 20, 2011

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Even though Edmunds has definitively debunked the myth of the 3,000-mile oil change, we keep hearing wildly contradictory information about engine oil, what type to use and how often to change it. So we issued a call for oil myths, legends and lies, and gathered up a list of the top puzzlers. We then put these questions to the experts and came up with some interesting answers. Here's a list of seven oil myths and realities to guide you through this murky subject.

1. Change your oil every 3,000 miles or three months — whichever comes first. We've said it before and we'll say it again: This is a myth for the vast majority of modern cars. The 3,000-mile oil change is the credo of the quick-oil change industry and dealership service departments, designed to regularly get you into the service bay. (Jiffy Lube recently abandoned its advocacy of the 3,000-mile rule, but clings to severe-schedule advice with which Edmunds disagrees. More on this later.)

Experts agree that the oil in today's cars should be changed at the designated intervals in the owner's manual or when the car's oil life monitor light appears. (The average interval for 2010 cars is around 7,800 miles.) Oil experts and car manufacturers say that oil chemistry and engine technology have evolved tremendously in recent years, extending oil change intervals.

"If customers always just stayed with the 3,000-mile recommendation, there'd be these great strides in the robustness of oil that oil companies have made [that] wouldn't be utilized," said Matt Snider, project engineer in GM's Fuels and Lubricants Group. Consumers, he said, would be "throwing away good oil" if they hewed to the outdated 3,000-mile rule.

2. Change your oil before a long road trip. There is some truth to this. It's definitely a good idea to look your car over before long drives, says Dan Edmunds, director of vehicle testing for Edmunds.com. However, if the oil change interval is not scheduled to occur during the trip, it is not necessary to change it preemptively. If the oil change interval would arrive during the trip, then it's a good idea to change it before you leave.

But Edmunds cautions that having service work performed just before a trip carries a risk. He was once driving miles from anywhere when a car passed him, trailing oil. It turned out the owner had just had her car's oil changed, and the shop had not properly tightened the drain plug. It had vibrated out. Edmunds suggests scheduling a service visit for about a week before leaving on a big trip, just to make sure everything is working properly before you hit the road. Here's more information about when to change your oil.

3. Nearly all cars should be serviced under the "severe" maintenance schedule. This oft-cited rule is a myth the quick oil-change industry (including Jiffy Lube) uses to bolster more-frequent-than-necessary oil changes, experts tell Edmunds.com. When manufacturers say "severe," they mean situations in which vehicles pull heavy trailers, or cars race on closed tracks. It also applies to taxis or emergency-response vehicles that can idle for hours at a time. Just plain old stop-and-go traffic doesn't automatically bump people into the severe schedule. For further proof, consider this: A number of automakers, including Ford and GM, contacted Edmunds data editors to request that the maintenance section of Edmunds' site substitute the normal maintenance schedule for the severe schedule that had been displayed. If your car has an oil life monitoring system the severe-versus-normal question is moot.

4. Check the oil on the dipstick. If it's black, change the oil. Experts say this is a myth, as is the related notion that you can identify spent oil by smell. "That is old school," says Kristen Huff, vice president of Blackstone Laboratories in Fort Wayne, Indiana. "Oil is meant to get dark — it means it's doing its job," she says. As GM's Matt Snider says in this video, different additives change the oil's color. The bottom line: Black oil still has plenty of life left in it.

5. When you buy a new car, change your oil at 3,000 miles to remove metal particles from the engine break-in process. There might be a grain of truth to this, according to the experts at Blackstone. Oil samples from engines during the first 3,000 miles of driving show elevated "wear-in" metal levels, coming from the pistons and camshafts, says Ryan Stark, Blackstone's president. But he added, "To me, it doesn't make that much difference because if the filings are big enough to cause damage, they will be taken out by the oil filter."

However, a Honda spokesman says its cars come from the factory with a special oil formulation for the break-in period. Honda advises owners to not change the oil early. Stark said Blackstone Laboratories' test of Honda's break-in oil shows it contains molybdenum-disulfide, an anti-wear additive. But Stark said Honda is the only manufacturer he knows that's using special break-in oil. The take-away? If there are any special break-in recommendations from the manufacturer, follow them. And consider analyzing the oil at 3,000 miles.

6. Once you use synthetic oil, you always have to use it. This is a straight-up myth. In fact, the line between synthetic oil and petroleum-based oil is blurring because the two types of oil are often blended, says Edmunds Engineering Editor Jason Kavanagh. "As long as the oil meets the service and viscosity requirements set out in your owner's manual, you can switch back and forth as much as you want," he says. For more information, watch this short video.

7. Synthetic oil is better for your car's engine and it improves your fuel economy. Myth. Steve Mazor, manager of the American Automobile Association's Research Center, says his testing shows that synthetic oil is generally a superior lubricant, but adds, "I'm not sure it is worth the extra cost — you need to take some of the [manufacturer's] claims with a grain of salt."

Blackstone's Stark says he has not seen data to support claims that synthetic oils boost increased fuel economy. "There is a school of thought that says the synthetic oils are slipperier and allow the engine to spin easier — I don't know that I believe that." Watch this short video for more on the ongoing debate over synthetic and conventional oil.

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