Q & A
I’d like to settle the oil change issue in my house once and for all. My wife wants to change oil in her car according to the manufacturer’s recommendation. In the case of her 1987 Acura Legend, that was every 7,500 miles. I did convince her to do it more frequently, so she changed oil about every 4,500 to 5,000 miles. I change oil in my 1993 Mazda MX6 every 3,000 miles, as I have always done in all my cars.
My wife says if the manufacturer’s recommendation was bad for the car they wouldn’t recommend it, because they want their cars to last a long time. She says the 3,000-mile oil change recommendation is from mechanics who want to sell their services and from the oil companies, which want to sell more oil.
I said I have been told repeatedly by mechanics that it is harmful to the engine to have dirty oil in the engine, and by 3,000 miles the oil is dirty.
What do you recommend and why?
Recently, when I had my oil changed, the shop tried to sell me an oil additive called Prolong that they said is an oil-based product and not like Duralube, which is Teflon-based. I declined. Before that, they wanted to sell me an “artificial oil” that they said costs a little more but will last much longer than regular oil. I declined that too because I believe natural oil is best.
What is your opinion on oil additives and on artificial oil, and why?
Arnold Berman
Via the Internet
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Let’s start with types of oil. There are three: mineral, synthetic and blends. Mineral oil is the kind that comes out of the ground. Synthetic oil contains no mineral oil and is formulated by engineers in oil company labs. Blends are combinations of the two.
Is one better than the other? Yes and no. The most important criteria to look for when buying oil are the service rating and viscosity range. For that, check your owner’s manual. Typically, the minimum American Petroleum Institute rating for gasoline engines is SG and for diesel engines it’s CD. (And the W part of the rating? It stands for winter, meaning the oil meets the viscosity standard at 0 degrees.) You’ll be hard-pressed to find a major brand that doesn’t meet or exceed that whether it’s mineral, synthetic or blend. Many meet the higher SH rating.
Synthetic or mineral? A quality mineral oil of the correct weight and service grade will do just fine. Do you drive really hard? In the desert? In a turbo? Pulling a boat? Then synthetic makes sense because the change intervals can be longer--two to three times longer. Of course, if you do drive a turbo hard while pulling a boat through the desert, you’ll want to change even synthetic oil every 3,000 miles.
Which brings us to your issue of domestic tranquillity. Vehicle manufacturers list two different intervals for oil changes. The longer one is for normal driving, which does not include short trips, stop-and-go, dusty conditions, extremes of heat or cold, or heavy use such as towing a boat.
Normal is basically a condition few of us see: Car is started. After a brief warmup (15 to 30 seconds), car is driven for a long enough period of time to bring it to normal operating temperature. During that drive, speed doesn’t vary all that much.
If your car is driven daily and used for commuting in the metro area, that isn’t so-called normal driving. So the shorter interval stated in your owner’s manual is the maximum distance or time you should drive before an oil and filter change. Does it make sense to change your oil earlier than the manual requires? Yes. The consensus is that the more often you change your oil, the longer your engine will last. Obviously, every 500 miles would be silly. But 3,000 to 4,500 is a reasonable amount of time.
More important, why is a shorter interval better?
Engine oil’s primary function is to lubricate metal parts and dissipate the heat from those moving parts so the engine doesn’t seize (but you knew that). It has additives that reduce friction and prevent foaming (which is really bad). It also holds byproducts of combustion in suspension, including silica and acids, along with metal that wears off moving parts. Oil also cleans the engine of these contaminants, which do a number on cylinder walls and rings. The worse the driving conditions, the more contaminants. The more contaminants per mile, the more often you should change the oil and filter.
What does Dr. Gear Head use? In my 4-year-old roadster, synthetic oil changed every 3,000 miles to 5,000 miles. I also use a premium synthetic gearbox and differential oil. In the aging SUV, it’s all mineral at the moment. Why? Because the engine needs a ring job, and with more than 150,000 miles on the clock, now is not the time to switch to synthetic. After its ring and valve job, I’ll probably change over. The main reasons are that synthetic sometimes dislodges deposits left behind by mineral oil, and seals and gaskets that have been exposed to mineral oil sometimes leak for a while after switching to synthetic. Not a lot, but enough to be annoying if your engine didn’t leak before.
The best approach is to pick one type and stick with it. If you buy a used car that’s been run with mineral oil and want to move up, go to a blend first or use a flushing oil (not kerosene!) between mineral and full synthetic.
Special note to new-car owners: While you may not be able to resist going 85 mph in your new auto, do have that first oil and filter swap done at 1,000 miles.
A brief word on additives, which I’ll discuss at length next month:
First, motor oil comes with additives. Dumping more of them in your crankcase doesn’t make motor oil better; in some cases, that can make it worse. The ones that are benign are a waste of money; the ones that aren’t could cause more problems than they are purported to alleviate.
Do I recommend them? No.
And neither do car manufacturers nor the oil companies that don’t market one of the popular miracle cures.
But, Doctor, you ask, what about the stuff racing teams use?
Well, do you drive your car at full throttle for 500 miles and then have the engine rebuilt? Although racing has been the field test for new technology, not everything used on the track makes sense on the street.
Finally, here’s a freebie: When you start a cold engine, let it idle for 15 to 30 seconds (air conditioning off, please). Modern cars no longer need to be warmed up to normal temperature before driving, but allowing the engine and oil to warm up a bit before driving off will add life to your motor.
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Sources: “More Than You Ever Wanted to Know About Motor Oil” by Ed Hackett, a chemist at the University of Nevada Desert Research Center, available on the Internet at https://www.vtr.org/maintain/oil-overview.html; “The Engine Oil Bible” by Chris Longhurst, also available on the Net, at https://www.geocities.com/MotorCity/2195/engineoil_bible.html; and Road Rider magazine, August 1992.
