Walking down the motor oil aisle can be overwhelming to those who are not familiar with oil viscosity. As you scan the wide array of oil weights and types on every shelf you may find yourself asking, “Which oil is best for my vehicle?” Since this depends on your engine, mileage, and the climate you drive in, it’s always best to consult your vehicle’s owner manual for the recommended motor oil viscosity before adding any oil to your vehicle. A lot of vehicles will also have it printed on your oil filler cap for an easy reference. Car manufacturers perform rigorous engine testing procedures to determine which oil viscosity will provide the most wear protection, as well as the recommended oil change interval.
What do motor oil numbers mean?
The numbers on oil labels are viscosity grades. They identify the thickness of the oil and its ability to flow at certain temperatures. This is commonly referred to as oil viscosity or oil weight. The numeric system used to classify motor oil and gear oil is determined by the Society of Automotive Engineers (SAE), which is why you may see SAE next to the oil weight on the bottle. If the number has a letter “W” (like 5W-30), the number preceding the W refers to the low-temperature viscosity, and the number without a “W” is the high-temperature viscosity.
Depending on the oil you’re shopping for, you may notice a single number like SAE 30, which are single grade or “straight weight” oils. Most engine oils will be multi-viscosity with a low- and high-temperature grade, like 5W-30 or 10W-30. Multi-viscosity blends are usually the best choice for most applications, as the oil provides protection in multiple climates or environmental conditions.
What is the risk of using lighter or heavier oil in your vehicle?
Using the wrong motor oil is still better than no oil, but using an oil that is too light or too heavy for your application does come with risks, and the effects may not be noticeable right away. An oil that is too thin will fail to provide the appropriate lubrication film for your engine’s internal components. This can cause increased wear on your engine. When engine temperatures rise, motor oil also becomes thinner. If your oil is already too thin, this can lead to further metal-on-metal contact and friction, reducing the life of your engine even further.
When your motor oil is too thick it will not flow as easily, and can fail to fill the gaps between the bearing surfaces of your engine components. Along with increased engine wear, you may notice increased engine temperatures, which can lead to faster oil breakdown and harmful sludge deposits. You may also experience a loss of fuel efficiency or difficulty starting your engine in cold weather.
What is the best oil for winter?
The “W” in the listed oil grade means winter. A lower number preceding the “W” indicates how the oil will perform in colder weather. If your oil has too high of a winter rating, it will be too thick in cold temperatures and will not flow as quickly as your engine may require. This can lead to difficulty starting your vehicle cold and added wear or damage on startup. However, following your vehicle manufacturer’s recommendations for oil type and service intervals is usually the safest and best option, since the manufacturer has already performed the needed research and engineering to determine the best weight of oil for your engine in any temperature. Modern vehicles may recommend viscosities as low as 0W-16, and older vehicles may recommend 10W-30, 10W-40, and even higher viscosities.
When to use heavier oil?
The short answer is, almost never. You may have heard higher viscosity oil is better, which is not typically true, and is a commonly-circulated oil myth. However, if you have an older vehicle that is running rough, has low oil pressure, or is experiencing oil burning issues, it’s possible a heavier viscosity oil may help your vehicle run better, and allow you to extend the life of your engine before serious repairs are required. The idea is that a thicker oil can better fill in the spaces between worn engine parts and bearings on a vehicle, as this wear can cause larger oil clearances. In the past, a vehicle running straight weight oil could see benefits from switching to a heavier oil. This is not so much the case for modern engines, which are designed with tighter oil clearances and intended for operation using lower-weight, multi-viscosity oils for better fuel efficiency.
If your engine has over 75,000 miles, a better option would be to switch to a high-mileage oil. These oils provide enhanced additives to help recondition seals, slow engine wear, and are designed to leak less through worn bearings and increased clearances.
Synthetic Oil
Automotive oil technology has come a long way. Modern vehicles are now often manufactured with synthetic oil in mind, which provides better engine lubrication, longer oil life, and often flow better in cold weather. If you are using synthetic oil, you will probably never need to switch oil weights due to weather conditions. Synthetic oil offers many benefits over conventional oil, including longer service times between oil changes.
For your next oil change, let our professional parts people help you find the right motor oil to best protect and extend the life of your vehicle. O’Reilly Auto Parts has all of the common motor oil viscosities, as well as high-mileage, synthetic, and conventional blends to ensure that your engine remains protected and your vehicle remains on the road as long as possible. If you’re looking for a proven synthetic oil, visit us in-store or online at OReillyAuto.com and see what high-mileage or synthetic oil, including Syntec full synthetic motor oil—exclusively at O’Reilly Auto Parts—can do for you and your car.
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