Oil Cap

Single Grade or Multigrade Oil: What’s the Difference?

Confused as to the difference between single grade or multigrade engine oil? Wondering which type you can safely put in your vehicle, or whether one might be better than the other when you’re staring down a rack of options?

You’re not alone. Fortunately, the answer is simpler than you might think. Let’s take a look at the key differences between these two classes of lubricant, and see where each one performs best in real-world driving.

Viscosity Is Key

All engine oil — synthetic or conventional — is classified according to its viscosity, which is really just a fancy term to describe how quickly it will flow through your motor at operating temperature (approx. 212 degrees Fahrenheit). Thinner oils flow faster than thicker oils, and engineers design engines with a certain oil viscosity in mind.

The Society of Automotive Engineers (SAE) classifies oil viscosity with a number. SAE 30 oil is thinner than SAE 40 oil and will flow more quickly. For normal driving, there is no advantage to putting a thicker or thinner oil in your motor than is recommended in the owner’s manual, and, in fact, you could harm the engine by doing so.

Not All Driving Situations Are Created Equal

Oil change

Not all driving environments are the same — they’re often differentiated by temperature. In fact, an oil that flows easily at 212 °F might thicken up and move more slowly once the temperature goes below freezing, which is a real problem for anyone starting a car in the morning after it’s been sitting all night in winter’s chill.

This is where the single grade or multigrade engine oil difference is most apparent. Multigrade oils are designed to have two different flows: one when it’s cold and one when an engine is warm. They are marked by a W, which stands for “winter.” For example, SAE 10W-30, with the number preceding the W indicates the viscosity of the oil when cold, and the number after denoting its viscosity when hot (at engine operating temperature or 212°F).

As you can see, multigrade oils start out performing like a thinner oil and then move up to a thicker specification once warm. This is crucial for protecting the inside of your car or truck’s motor when you first turn the key on an ice-cold block, as the low viscosity number ensures it can pump rapidly and provide a protective coating to your engine’s components almost immediately.

Is There a Single Grade Advantage?

The case for single grade or multigrade oil might seem clear-cut in favor of the latter. Still, there are very specific cases, like lawn mowers, where a single grade lubricant is commonly used.

In summary, there are certain applications where a simple single grade oil, or monograde oil, is suitable for use. However, you will not go wrong choosing a multigrade viscosity engine oil because they provide a wider range of temperature performance. And remember that the viscosity measurement rules are the same whether you choose a normal conventional motor oil, or a high tech natural gas derived full synthetic motor oil like Pennzoil Platinum.

For more information on single grade or multigrade oil, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Wikimedia Commons.

about author

Benjamin Hunting

Having been bitten by the car bug at a young age, I spent my formative years surrounded by Studebakers at car shows across Quebec and the northeastern United States. Over ten years of racing, restoring, and obsessing over automobiles lead me to balance science writing and automotive journalism full time.  I currently contribute as an editor to several online and print automotive publications, and I also write and consult for the pharmaceutical and medical device industry.

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