Should I Switch to a Lighter Viscosity Oil in Winter?

Motorists sometimes ask if they should use a lighter viscosity of motor oil once winter arrives.

Yes – provided your vehicle manufacturer allows it. 

Run out to your vehicle and fish the owner’s manual from the glove box. Or open a digital copy on your phone.

Somewhere in the back you should find the motor oil recommendations. Many vehicles, particularly domestic, call for a lone viscosity of motor oil. It’s likely 5W-20 or 5W-30. That’s what you’re supposed to use all the time. Doesn’t matter if it’s -20ºF (-29ºC) or 100ºF (38ºC) outside. The engine was designed and manufactured to operate most efficiently using that particular viscosity of motor oil.

But some vehicle manufacturers – often foreign – recommend different motor oil viscosities depending on ambient temperature. You may find a chart in the owner’s manual like the one below that shows which viscosity you can use depending on the temperature. The manufacturer typically recommends a lighter viscosity when the temperature drops during the winter.

Your vehicle owner’s manual may contain a viscosity chart like this one.

In this case, we recommend using the lightest recommended viscosity during the winter.

Why?

Two reasons:

  • Maximum wear protection at startup
  • Easier cold starts

To understand, you have to understand motor oil viscosity. If you’ve navigated to this page after a Google search, you probably know something about viscosity already. But a little refresher can’t hurt. (Check out this post for a detailed explanation of viscosity.)

Viscosity refers to the oil’s resistance to flow and is its most important property. The lower the oil’s viscosity, the more readily it flows at cold winter temperatures. Of course, the opposite is true – the higher the oil’s viscosity, the more slowly it flows when cold. That means an 0W-20 oil will flow better when it’s cold than a 10W-30.

Dub-ya

Which brings me to my next important point.

The oil’s “W” viscosity describes its characteristics when it’s cold. And by “cold” we mean 40ºC (104ºF). The second number (e.g. the “30” in “5W-30”) describes the oil’s characteristics once your engine reaches normal operating temperature, or 100ºC (212ºF).

Engineers agree that most engine wear occurs at startup. One reason is because gravity pulls much of the oil into the sump as the vehicle sits overnight.

When you start the vehicle the next morning – even if it’s not that cold outside – a few critical moments pass before the motor oil travels through the oil pump and navigates the narrow oil passages to reach components throughout the engine. It’s during those moments that accelerated wear can take place.

As such, it’s beneficial to use an oil that flows readily at startup to reach engine components as quickly as possible.

Since lower-viscosity oils flow more readily, they provide better cold-weather startup protection compared to higher-viscosity oils.

Crank it up

Lower-viscosity oils also provide less crankshaft resistance as the engine turns over. When the temperature plummets below zero, the motor oil can thicken so much that it prevents the crankshaft from spinning fast enough to start the engine. This is particularly a problem with conventional oils since they contain waxes that thicken in the cold. Synthetic motor oil, in contrast, doesn’t contain waxes and, therefore, provides easier cold starts.

Check out the video to see for yourself.

video
play-sharp-fill

Along the same lines, oil that provides less resistance to moving engine parts also maximizes fuel economy. That’s the primary reason automakers are trending toward lighter viscosity oils in their new vehicles.

A word of caution…

It’s important to note that using a higher-viscosity oil does have its benefits, too. Higher viscosity oils tend to provide improved wear protection since they promote formation of a thicker fluid film on engine parts. They’re also more resilient to oil consumption than lighter viscosities.

Bottom Line: Switch to the lightest viscosity oil your vehicle manufacturer recommends in the winter. Doing so maximizes wear protection at startup while improving cold-weather starts.

FIND AMSOIL PRODUCTS FOR YOUR VEHICLE

Oil Analysis Kits Available from Oil Analyzers Inc. Ed Newman|May 10, 2022 2:38 PM   In order to provide a cost-effective oil analysis option when a full fluid analysis is not required, Oil Analyzers Inc. has launched a new Oil Analyzers Value Kit that focuses on the most critical used-oil analysis tests. It provides less […]

Racer Secrets: Tips and Tricks to Help on Race Day Lindsay Premo|Oct 16, 2020 8:00 AM Happy October, race fans! There are a lot of things we know are necessary in racing. A helmet, driver’s suit, gloves, appropriate footwear and (obviously) something to race on/in are all essential to striving toward that checkered flag. But, […]

First Time Heading to Sturgis? We’ve Got Some Tips. Jamie Jarvi|Aug 03, 2016 9:26 AM The Sturgis Motorcycle Rally is a true bucket-list destination for any motorcycle enthusiast. Each year thousands upon thousands of riders descend on Sturgis, S.D., and turn this small, sleepy town into a motorcycle mecca. Some travel the road to Sturgis […]

AMSOIL synthetic motor oil helps you breathe easier Oxygen is great in your lungs, but it’s not so great in your motor oil. Matt Erickson | VP, PRODUCT DEVELOPMENT Oxygen comprises about 20% of our atmosphere. It’s the third most common element in the universe. Without it we’d all be doomed. Yet, oxygen can cause […]

How to Maximize Marine Engine Performance and Reliability John Baker|May 02, 2022 10:36 AM   Fishing opener is right around the corner for us Northlanders. It’s essentially a regional holiday, rivaled only by the opener of gun deer season in the fall. Although some boaters and anglers don’t realize it, using a dedicated marine motor […]

Zeroturn Spindle

Best Practices for Your Zero-Turn Mower First, we’ll start with a question. How did we survive before Zero-Turn mowers? What did they do in the 50’s? Did they not cut the grass? Chris Sharon|Sep 07, 2022 8:00 AM Here at AMSOIL, we’re always investigating ways we can help you get the most out of your […]