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Should You Use Synthetic Oil for Winter?

Close-up of a red vintage oil can

Most car owners are aware of the oil basics: Use the correct oil viscosity, and change it on time. While these two points are widely accepted, there’s still some debate about using conventional oil versus synthetic oil. Most automakers specify using synthetic oil in new vehicles, but what about your not-so-new vehicle? There are good reasons to use synthetic oil for winter and even year-round.

A Refresher on Cold Temperatures and Oil Viscosity

If you use synthetic oil in winter, you can prevent premature engine wear.In general, multigrade oils improve cold-start lubrication while offering excellent protection at engine operating temperatures. Consider a typical multigrade 5W-20 engine oil, used in many late-model vehicles on the road: “5W” refers to winter viscosity, or how well the oil flows at zero degrees Fahrenheit, and “20” refers to operating temperature viscosity, measured at 212 degrees Fahrenheit.

Most vehicles specify a single multigrade oil, such as 5W-20 or 10W-40, to be used year-round in all ambient weather conditions, but some may call for a lighter multigrade oil in winter, such as 5W-40 instead of 10W-40. Note how only the first specification changes — further improving cold-start characteristics without sacrificing performance at normal operating temperature. Given expected ambient temperatures within your oil change interval, choose an engine oil with the lowest winter viscosity recommended by the owner’s manual.

Synthetic Oil Has More Consistent Cold-Temperature Performance

If you’ve been using conventional oil, there is good reason to switch to synthetic oil for winter. Because conventional oil is refined from raw petroleum deposits, it contains various contaminants that cannot be distilled or filtered out. For example, at room temperature, the waxes in conventional oil remain dissolved and barely affect oil viscosity. As these wax molecules get colder, though, they begin to crystallize and clump together, significantly increasing the oil’s viscosity.

Increasing viscosity coupled with decreasing temperature is exactly the opposite of what your engine needs for a cold morning start. Increased oil viscosity leads to poor cranking performance, excessive starter and battery wear and increased engine wear in bearings and on cylinder walls. As conventional oil wears, oil additives burn off or evaporate, and the viscosity differences become even starker.

Using synthetic 5W-40 instead of conventional 10W-40 in your turbo diesel engine can significantly improve cold-starting without sacrificing protection while towing and hauling. Synthetic oil doesn’t contain any wax, so it doesn’t thicken up as much as conventional oil in the cold. In fact, synthetic oil doesn’t contain any of the contaminants found in conventional oil, so it performs more consistently, even in extreme temperatures.

Back to Basics

Whether you use conventional or synthetic oil, be sure to follow the oil basics. How often you need an oil change depends on your driving habits more than your vehicle. Some drivers might need an oil change every six months, others every two months. It’s determined by mileage, usage and time. Also be sure to use the right oil viscosity, as the wrong viscosity can lead to a lack of lubrication and premature engine damage.

Check out all the oils and lubricants available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on engine oil, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Pixabay.

Benjamin Jerew View All

Ben has been taking things apart since he was 5, and putting them back together again since he was 8. After dabbling in DIY repairs at home and on the farm, he found his calling in the CGCC Automobile Repair program. After he held his ASE CMAT for 10 years, Ben decided he needed a change. Now, he writes on automotive topics across the web and around the world, including new automotive technology, transportation legislation, emissions, fuel economy and auto repair.

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