By Catherine Simpson
How often should you have your oil and filter changed? All the "quick lube" places tell you 3 months or 3000 miles. Clark Howard challenges that, and says you may be able to go at least 5000 miles. Your owner’s manual may indicate your vehicle is fine for 7,500 miles. Why all the differing opinions, and more importantly, who should you listen to? Well, the short answer is – it depends!
One fact that the automotive industry will agree on is the importance of regular oil changes to prolong the life of your engine. But just how regular those oil changes need to be varies due to several factors. First, and often most confusing, is the issue of "normal vs. severe" driving conditions. Most owner manuals will have two different maintenance schedules based on these definitions – with "normal" allowing for less frequent servicing, and "severe" requiring heavier service. Many customers tell us, "Oh, I don’t drive too much, just around town," assuming that puts them in the less severe category, when usually the exact opposite is true.
Ideal, or "normal", driving conditions – in other words, what your engine prefers – is trips over 10 miles, cruising on the highway, at moderate temperatures and loads, in a relatively clean-air environment. If your driving habits fit this category, you may not need your oil changed as often. "Severe" driving consists of short or frequent trips less than 10 miles, extreme outdoor temperatures, stop-and-go city driving or extensive idling in traffic, towing or heavy loads, and a dusty or polluted environment. If any of this description fits your driving profile, then your engine would appreciate more frequent oil changes.
How do these different driving conditions affect the engine oil? Driving with the engine cold or under heavy loads, for example, requires more gas; but this excess gas can result in unburned fuel slipping past the engine piston rings, and contaminating the oil. Also, normal condensation in the engine crankcase does not sufficiently burn off when the engine is not allowed to reach and/or stay at operating temperature due to short driving trips. This moisture accumulation causes "sludge" buildup over time, which can clog oil passages and damage the engine.
These same combustion by-products that contaminate engine oil more easily with "severe" driving conditions also usually increase in older cars and/or higher mileage engines. Newer cars tend to have improved emission controls that produce cleaner running engines and don’t contaminate the oil as quickly. The same holds true for well-maintained cars; an old air or fuel filter and worn-out spark plugs will create more contaminants that can make the oil dirty and abrasive.
Then there’s also the dreaded "months vs. miles" question, and which is best to follow. Let’s say six months have passed since your last oil change, but you have only driven 3,000 miles. Look at the nature of those miles – are they low because you took MARTA to work and let your car sit in your driveway most of the time? Or did you drive 15 miles every day, but sit in traffic for over an hour to make those miles? If so, remember that your engine is working just as hard idling during that hour as it would be accumulating miles. It would be more accurate if there was a way we could measure oil change intervals by number of engine revolutions rather than by miles.
Another factor in this debate is your long-term goal with your vehicle. For example, do you like to trade in your car for a newer model every three years, or do you plan on still having your car 8 years from now, or more? If you are the type who wants an engine to last as long as possible, frequent oil changes are your best bet. But if you rarely keep a vehicle with a mile over 30,000, then long-term preventive maintenance is probably not your biggest concern. However, one thing to remember is that proof of regular maintenance can increase your car’s re-sale value to an individual, as well as uphold your manufacturer’s warranty.
The type of oil you use – regular or synthetic – also comes into play here. We won’t examine the pros and cons in this article of which to use as that is a much lengthier discussion. However, most automotive experts contend that the oil change interval can be extended safely up to 10,000 miles when using synthetic oil.
One more point to bear in mind is that an "oil change" is usually more than just replacing your engine oil and filter. It’s a time for your fluids to be checked and topped off; tire pressures to be adjusted; belts and hoses to be inspected. If you regularly do your own 21-point inspection, then frequent trips to a repair shop or oil change facility may not be as high a priority for you. But if a tire gauge and a transmission dipstick are foreign items to you, regular visits to a mechanic that you trust may give you peace-of-mind. Granted, you could schedule regular car check-ups without having the oil changed, but the cost would end up about the same.
Now let’s do some math. Over a period of 100,000 miles (which is 8 years for the average driver), following the 3,000-mile interval will result in 33 oil changes. Assuming the average price of an oil change (using regular, not synthetic, motor oil) to be $20 - $25, the total cost will be $660 - $825. Increasing the interval to 5,000 miles and 20 oil changes, the total cost decreases to $400 - $500. And the respective numbers for a 7,500-interval are 13 oil changes at a cost of $260 - $325. The greatest possible savings are $565 which, when divided over an 8-year period, averages out to less than $6 per month. This cost can be viewed as cheap insurance against a possible $4000 replacement engine. (There is an environmental angle to consider here as well: some argue that it is a waste of natural resources to replace your oil and filter more than is necessary, but others assert that infrequent oil changes contribute to decreased fuel economy and increased emissions.)
We at Catherine’s Auto Repair recommend replacing your engine oil and filter every 3 months or 3,000 miles as a general guideline. But you are the one who needs to take into account your individual circumstances and personality type. What are your driving habits and environment? How old is your car and how well do you maintain it? How long do you intend to keep your vehicle, and are you concerned with the re-sale value? What kind of oil do you use? Do you perform routine inspections on your car, or rely on your repair shop for that service? Where do you place yourself on the "fear factor" spectrum with respect to your car, i.e., would you rather play it safe and maybe pay a bit extra, or do you favor saving some money while knowing there are some risks? And finally, are you a procrastinator? If you aim for a 3,000-mile interval, will you eventually get around to it by 4,000? If your goal is 7,500, will you push it as far as 10,000? You are the only one who can weigh all these considerations, and then make a decision that will serve you and your vehicle best.
