There’s no better way to get an argument started among a bunch of automotive guys than to bring up engine oil. Everyone has a favorite brand, and most will defend it with his or her dying breath. But unless you’re immersed in the automotive enthusiast culture, oil can be a slippery topic. With so many brands and types available, it can be confusing as to what to purchase for your vehicle. Do you need synthetic? What about a high-mileage oil? Maybe one with wear inhibitors? So many choices!
In truth, there’s really no need to fret when it comes to choosing the right oil for your vehicle. If you understand a few basic terms and know what to look for (and where to find it), you can be assured that you’ll always make the right engine oil purchase.
Understand the Labels
So you’ve got a quart of oil in your hand and you notice these funny round labels with a bunch of numbers and letters (see photo); just what does all that gibberish mean? In a nutshell, they tell you if the oil is appropriate for your vehicle.
The donut-looking label shown above tells you the “service classification” of the oil as determined by the American Petroleum Institute (API)—in this case it’s “SN”—as well as the oil’s viscosity.
When motor oils were first developed, they carried a “SA” rating and were appropriate for automobiles built in 1930 or earlier. As oils developed and improved, they were reclassified as SB, SC and so on. Today’s SN rating was introduced in 2010 to provide better engine protection for 2011 and newer vehicles and is the most current motor oil available. (Oils with a SJ, SL, and SM rating are also still available and are also considered a “current” motor oil and safe for use—see photo.) Do not use old oil rated SH or older—and yes, they’re still out there—as they won’t provide adequate protection for your engine.
The Society of Automotive Engineers (SAE) viscosity rating listed on the donut label tells you how viscous the oil will be in both cold and hot conditions. Viscosity (a fluid’s resistance to flow) is rated at 0° F (represented by the number preceding the “W” [for Winter]) and at 212° F (represented by the second number in the viscosity designation)—the smaller the number, the thinner the oil. So for example, a 5W-30 oil has a winter viscosity of 5 and a viscosity of 30 when hot.
So why is this important? At the low-temperature end, oil has to be resistant to thickening so that it flows more easily to all the moving parts in your engine. For example, a 5W oil will flow much easier in cold temperatures than a 20W oil. Once the engine is running, the oil heats up, and the second number in the viscosity rating tells you that the oil will stay thicker at high temperatures than one with a lower second number. So for example, a 10W-40 oil will stay thicker when it heats than a 10W-30 oil.
One last thing to look for on the donut label is the words “resource conserving” or “energy conserving.” If you see either of those ratings, it means that the oil may help in overall fuel economy. And along with the donut you’ll see a symbol that looks like a toothed gear that tells you two things: first, that the oil has been certified by the American Petroleum Institute; second, that the oil is intended for gasoline engines.
When choosing the right viscosity of oil, always refer to your vehicle’s owner’s manual. It will list what is appropriate for different driving and environmental conditions.
Types of Oil
No longer available as simply conventional or synthetic, oils now come in a wide array of formulations.
- Premium Conventional Oil—made from naturally forming petroleum, this is the standard new-car oil that requires changing regularly at set intervals.
- Full Synthetic Oil—without getting crazy technical (as there are three different grades of synthetic oil), these oils are made from either petroleum base or a full synthetic base. Either way, they’ve been distilled, purified and broken down into its basic molecules in order to remove more impurities and enable individual molecules in the oil to be tailored to the demands of modern engines. They have superior, longer-lasting performance, they flow better at low temperatures, and they maintain peak lubricity at high temperatures. Not all cars, however, should use them, so always follow the recommendations in your owner’s manual.
- Synthetic Blend Oil—these have a dose of synthetic oil mixed with organic oil, and overall are formulated to provide protection for somewhat heavier loads and high temperatures. They’re popular with drivers of pickups/SUVs who want the high-load protection, and they’re a lot less expensive than full synthetics.
- High Mileage Oil—made for today’s longer-lasting vehicles, these oils have additives that help with restoring seals to their original shape and flexibility, help restore the valve seals, seal piston-to-cylinder clearances better, and contain a higher dose of anti-wear additives to help slow the wear process.
In order to make today’s oils as magical as they are, petroleum companies blend special chemicals into the oil during the refining process. These chemicals—known as additives—give oil the performance boosters they need to do their job. Common additives include:
- Viscosity-index improvers to reduce oil thinning
- Detergents to remove deposits and inhibit the formation of rust and corrosion
- Dispersants to reduce sludge, varnish and acids
- Anti-wear agents to protect metal surfaces
- Friction modifiers to reduce engine friction and improve fuel economy
- Pour-point depressants to enable the oil to flow readily at low temperatures
- Antioxidants to prevent oxidation (and thickening) of oil
- Foam inhibitors to prevent the oil from breaking down in the oil pan
- Rust/corrosion inhibitors to protect metal parts from acids and moisture
If all this sounds arcane, it’s really not. If you always check your vehicle’s owner’s manual for the type of oil recommended by the manufacturer, you’re well on your way to buying the right kind. Just match the viscosity to the recommendation, pick a type that’s best for your vehicle’s mileage or age, and you’re well on your way to a satisfyingly slick experience.