Oil Weight: What It Means, and Why You Might Want To Use Different Oil In Winter

Viscosity and Old Man Winter’s cold don’t mix, and that could mean trouble for your engine.

Andy Stonehouse | 

Oct 21, 2022 | 3 min read

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You count on your car to start, especially if you live in a place where it gets cold. No one wants to be stranded when their car doesn’t start in the middle of winter. There’s many ways to help your car run more efficiently during the colder months, and the weight of your oil could play a key role in keeping you on the road.

Understanding the basic science behind oil weights, as well as the vital information contained in your owner’s manual, can help you make the right decision.

What is the difference between oil weights?

The numbers on the label of a quart of engine oil (a common example is 10W-30) refer to viscosity, the thickness and flexibility of the oil in different temperatures. Think of viscosity like maple syrup. Warmed-up maple syrup flows more easily onto your pancakes, while cold syrup is as thick and slow-moving as molasses.

To keep your engine operating at maximum efficiency in different temperatures, you’ll want to use a lower-viscosity grade oil that allows it to remain more fluid in frigid temperatures.

That number, set by the Society of Automotive Engineers, will allow your car to start and run more easily with less friction. A higher-viscosity oil will provide better oil pressure, and allow the oil’s thickness to provide more protection while your engine is running.

A multi-weight oil like a 10W-30 is designed to have a broader range of effectiveness — the first number and the “W” indicate the rating for winter/cold start-ups, and the higher number applies to viscosity at operating temperature. Multi-weight oils are basically like having two different oils, whereas conventional single-weight oils are only rated for their efficiency at operating temperature.

What weight should I use?

The cardinal rule for oil choice in your engine still lies with your owner’s manual. Take a look and you’ll see specific information provided by your carmaker regarding the weight, and maybe even the recommended type (synthetic vs. traditional oil), or if they officially recommend particular winter or summer oil weights.

For the most part, you’re still free to pick the brand, but the specifics of the oil weight, plus the option to use different weights at different times of year, should be followed to the letter – plus the timing/mileage figures for oil changes.

Subbing in a different oil for winter

The story changes if you have a car that recommends a range of lower-numbered, lower-viscosity oils during the winter. Choosing one of those with the lowest number allowed by the manufacturer will mean easier starts when the thermometer drops, and will also mean better engine protection when you fire the ignition versus thicker oil that’s so cold it can’t flow easily throughout your engine’s parts.

If you’ve moved from a place like Atlanta to Northern Maine or Fairbanks, Alaska, it’s definitely a good idea to consult with a local mechanic and see if they have suggestions about using a thinner-viscosity, multi-weight oil to help ensure easier starts. A plug-in electric engine block heater is an entirely different option, but is designed to warm up key engine components and make starting easier in extreme cold conditions.

Synthetic oil — which is a combination of traditional petroleum products and chemical additives to extend its life, and offer more engine-cleaning and lubricating qualities — may also be a recommended option to help provide more flexibility during the winter.

Andy Stonehouse

Andy Stonehouse literally fell into the world of auto writing while working as a ski-town journalist, and has not looked back since. A childhood spent dealing with the eccentricities of a 1976 MG Midget has made any subsequent auto experience a more safe and reliable drive. He has been blessed with nearby mountain trails and snowy roads in Colorado to do TV-adventure-styled test drives on a weekly basis.