If you’ve been to a dealership, mechanic, or oil change shop in the last few years (and you have, a few times at least, right?!) you know that choosing the right type of oil for your car is more complicated than ever. Which brand should you use? What weight of oil? Synthetic or standard? Fortunately, choosing the right oil for your car is simpler than it looks.
Cutting straight to the chase, the easiest and most correct answer is (almost) always right there in your glovebox: the owner’s manual. You car’s owner’s manual or its service addendum will state exactly what type of oil to put in your car. You may hear things like “heavier oil is better in winter” or “lighter oil is better in summer” or “lighter oil will get you better fuel economy” or “heavier oil will protect your engine better”—but with few exceptions, these are all old wisdom, no longer applicable to today’s cars. The simple truth is that the manufacturer knows best what will work in your car’s engine, and that oil was chosen to work in all environments, under all use conditions, all the time.
Often, the owner’s manual will even suggest an oil brand. If your manufacturer makes such a recommendation, you can’t go wrong with meeting it, especially if your car is still under warranty. Failure to comply with the recommended maintenance may void parts of your warranty.
For older cars, or cars where the warranty no longer applies, or for those seeking to save a little money over the name-brand oils, there are alternatives that are still completely safe and appropriate for your car. The most important aspects of the oil in your engine are its weight and whether it’s synthetic or standard. Name-brand oils typically include special additives that claim to reduce wear, enhance lubrication, or perform other functions like cleaning away deposits, but the bottom line is that most oil is just oil—and it’s mostly perfectly good.
So what do you need to know to pick the right (and affordable) oil for your car? Almost all oil used in cars built in the last 25 years is a multi-weight oil. That means it has two numbers, separated by a W, i.e. 5W-20. The first number indicates the oil’s viscosity at 0 degrees Fahrenheit (for winter cold-start conditions) and the second denotes the oil’s viscosity at 212 degrees Fahrenheit. Smaller numbers mean lower viscosity, which means the oil is “thinner” and flows easier; larger numbers mean higher viscosity, which means the oil is “thicker” and can better coat parts, or resist the heat-related thinning that all oil experiences.
Then there’s the difference between conventional, or standard motor oil, and synthetic oil. While the technical differences boil down to manufacturing processes and testing regimens, what the differences mean to you is much simpler: synthetic oils are purpose-made for high-tech or high-performance engines, and often have better performance characteristics than conventional oils. But that doesn’t mean they’re always the best choice—and they’re often more expensive. Conventional oils may be less capable in some respects, but are still very good oils, which still meet the needs of most car engines. Synthetic blend oils combine synthetic and conventional oil in differing proportions to achieve the desired result. Look for the API (American Petroleum Institute) certification seal on any oil you choose for your car, whether it’s conventional, synthetic, or a blend.
Finally, there are “high mileage” oils, intended for older cars with more miles on the clock. These come in both conventional and synthetic forms, but all high mileage oils include seal conditioners that help prevent older cars from leaking oil, as well as (typically) higher viscosities and viscosity index additives, to help better keep your engine functioning as it was intended, despite internal wear due to its high mileage.
If all of this sounds incredibly confusing, that’s because it is—unless you’re an engineer or oil chemist. But the bottom line is that choosing the right viscosity or weight—the one recommended by the manufacturer—is the most important aspect of choosing the right oil. After that, the choice between synthetic and conventional (unless synthetic is specifically required by the manufacturer), high-mileage, brand, and additives is up to you and your budget. So next time you go to get your oil changed, you’ll be armed with more complete knowledge and the confidence that you’re making the right choice for your car.
For more about oil changes and what you need to know, don’t miss our first part in this series here, and look for the third part, which will examine the other services often bundled with oil changes—and whether you should have them done—to come soon.
automotive freelance journalist