With winter in full swing, especially if you live north of the 40th parallel, you might have to start your car in below-freezing temperatures, perhaps even below zero. Depending on what kind of oil your car has, you could be inadvertently damaging your engine with every cold start. For this reason, automakers may recommend using a different oil for winter in your car’s manual. Here’s why.
What Is Oil Viscosity?
Oil viscosity describes how well oil flows at a given temperature. To measure oil viscosity, a lab technician calculates its resistance to flowing through a thin glass tube. Thicker oils take longer to flow through the tube than thinner oils. The more resistant an oil is, the higher its viscosity. Picture honey flowing through one glass tube and water flowing through another. Which will take longer? You guessed it: Honey has a higher viscosity than water.
When the weather is warmer, oil flows more easily. In other words, high temperatures lower oil’s viscosity. Imagine the difference between the thickness of honey kept in the refrigerator and honey warmed on a stove, for example.
How Is Oil Viscosity Measured?
An engine oil’s viscosity is measured at two temperatures: 100 and 210 degrees Fahrenheit. If you look at the labels of engine oils, you’ll see they’re marked with letters and numbers, such as 0W-20 and 5W-20. The 0W and 5W refer to viscosity measured at 100 degrees, while -20 refers to viscosity measured at 210 degrees. At engine operating temperature, both oils will exhibit the same resistance to flow. When cold, though, the 0W-20 will flow better than the 5W-20.
Why Do Some Vehicles Need Different Oil for Winter?
Because lower viscosity means less resistance to flow, it’s logical to conclude that a low xW grade will make a good oil for winter. You should use oil with the same -XX grade, which signifies what your car needs your oil’s viscosity to be at engine operating temperature, throughout the year. Going into winter, it’s a good idea to check your owner’s manual to see if a lighter xW grade oil is acceptable. This information is usually presented in a “recommended viscosity” chart. Many vehicles specify a single multigrade oil, such as 5W-20 or 0W-20, no matter which temperature the vehicle will be operated in, but some may recommend using two or more different oils, depending on expected temperatures.
If your vehicle can take a lighter oil in winter, it’s a good idea to get an engine oil change just before expected temperatures warrant it. For example, if your engine specifies 10W-30 for temperatures over zero and 5W-30 for all temperatures, you can safely switch to 5W-30 when you’re expecting temperatures below zero. This will ensure good lubrication on cold starts and better engine protection. Of course, you could run 5W-30 all year long for better fuel economy.
Check out all the oils, grease 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 choosing the right oil, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.
Photo courtesy of Pixabay.
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.