Walk into the oil section of your local auto shop and chances are you'll face a mind-numbing selection of motor oils in a variety of grades from a plethora of manufacturers. If you walk in with no background on the subject of motor oil, it can be difficult to tell each apart or know which one will work best for your beloved auto. Is regular oil better than synthetic? What do all those numbers on the front of the bottle mean? The good news is it's not as complicated as it seems. Let's break it down.
The Numbers Game
Take a look at the numbers on the labels. You may see 10-40, SAE 30, 20w-50, etc. These digits correspond to a set of measurable qualities in the oil, one being the viscosity index. Viscosity is the oil's resistance to flow. The higher viscosity of an oil (or thicker, if you will), the slower it flows. A lower number refers to thinner, or faster-flowing oil. So how is the number discerned?
First we'll start with single-grade motor oils, which, you guessed it, feature a single number rating. Single-grade motor oil (which doesn't use a polymeric Viscosity Modifier, FYI) is good for classic or vintage cars. The viscosity of this oil is measured when the oil (non-winter grade) is heated to 210°F, which is considered to be the approximate automotive engine operating temperature. Based on its resistance range at this temperature, the oil is then graded as SAE 20, 30, 40, 50, or 60; the higher the viscosity, the higher the SAE grade. A quart of the pictured Valvoline Premium Conventional SAE 50W Motor Oil 1-Quart Bottle ($7.34 with free shipping, a low by $5) serves as a good single grade oil.
Multi-viscosity oils, then, feature two numbers in their ratings. The left number refers to the oil's behavior in colder conditions, while the right number signifies its behavior in warmer conditions. Multi-viscosity oils not only feature two numbers, but also include a 'W' which conveniently stands for "winter." These motor oils were developed to compensate for engine wear that results from temperature extremes.
Today, multi-viscosity oils are used almost exclusively over mono grade oils since they function best in both climates, if you will. An SAE 30 motor oil, for example, is consistent with the viscosity of, say, a 5W-30 oil when both are at 210° F, but the latter offers better performance in the cold as well. Multi-viscosity oils also contain additives that keep the oil from thinning out as its heated. A Castrol GTX High Mileage 10W-40 Motor Oil 5-Quart Jug ($28.99 with pickup, a low by $2) is a great pick at just $5.80/quart.
So the next question you're probably asking is: does motor oil differ by brand? The short answer is yes. A 5W-30 oil from one brand may be equivalent to a different brand's 10-40 simply because there is a variance in some of the oil's other properties. Honestly, the best advice we can give is to ask your local mechanic, or a friend that knows cars, and go with a trusted, reputable brand.
Synthetic Oil? (I Prefer the Term "Artificial" Myself)
In the early '70s, AMSOIL brought the first synthetic automotive motor oil to market, and it's still considered to be one of the better oils for diesel motors. As such, the Amsoil Synthetic Blend 15W-40 Heavy Duty Motor Oil 12-Quart Case ($80.40 with $11.84 s&h, a low by $36) is a good bet at just $7.69/quart. Later in the decade, Mobil Oil then released its first synthetic motor oil, and by the '90s, other major oil companies had joined in.
So what's the big to-do then about synthetic motor oil? While most people will claim that the synthetic blends are better in almost every way, understand that artificial motor oil is also much more expensive. In reality, synthetic motor oil does offer better low-temperature flow, and better high-temperature resistance, and leave close to zero deposits. Because synthetic oil flows so much better and features a greater ability to penetrate than regular oils, switching to synthetic oil might reveal leaks you didn't even you know you had.
And though, while expensive, you can still find deals on synthetic motor oil (with our assistance perhaps). Another top-selling option, in addition to the aforementioned Amoil, is the Mobil 1 10W-30 Full Synthetic Motor Oil 6-Quart Case ($36.16 with pickup, a low by $24; a close price, $36.99 with pickup at Advance Auto Parts), which will set you back just $6.03/quart.
Oil Considerations for Older Cars
As your car ages, gaps between engine parts grow larger, which in turn, causes less oil to reach its critical parts. A lot of experts say that as a car ages, owners should switch to a higher-viscosity oil. If your ride is over the 80,000 mile mark, check with your mechanic or someone familiar with your car (or if in doubt, ask the dealership) and determine if you should swap out the current type of oil in your vehicle.
High mileage older vehicles, more often than not, have lots of mechanical wear in the engine, which in turn can create internal oil leakage. Car makers use full synthetics and semi-synthetics in some of their engines today; in most cases, you will find that a full synthetic lubricant is more commonly used in high-performance applications when there's an engine with very tight tolerances, high engine temperature, or high compression applications (such as a supercharged or turbocharged motors).
It's not recommended to use full synthetic oil on high mileage vehicles, because the oil is thin and very free flowing. We'd suggest a full-bodied semi-synthetic oil instead. (Almost sounds like we're talking about wine rather than motor oil, eh?) An awesome semi-synthetic motor oil is the pictured quart of Lucas 10W40 Semi-Synthetic Motor Oil ($5.24 with $6.99 s&h, a low by $2).
We hope this helped clear some of the confusion as to motor oils and what all the numbers and types mean. By all means, use this as a guide, but check with your dealer or trusted mechanic before making any major switches to your vehicle. That will save you plenty of headache and heartbreak down the road.
Front page photo credit: Baba Wheels