Grading Oil

motor oil

Did you know that the “w” in your oil weight means “winter”? Most of us aren’t old enough to remember when it was necessary to switch to a thinner oil in winter, and a thicker one in summer. The switch was necessary because the thickness of an oil (the viscosity) varies with the temperature outside. Oil is thinner when it’s hot, and thicker when it’s cold. It might help to think of molasses. If you heat it up, it pours more quickly.

But your engine needs a consistent viscosity. That’s where motor oil grades steps in.

The Grading System. When you measure viscosity, you’re measuring how fast a liquid flows at 100 degrees Celsius. (You get an A plus if you remember that’s also the boiling point of water.) A higher number means the oil is thicker and will flow more slowly. A lower number is the opposite; it’s thinner and flows more quickly. Again, like molasses.

Fun Fact: Apparently the Egyptians used animal fat to lubricate wheels as early as 1700 BC!

The Upgrade. In the 1950’s, the Chevron Oil Company developed the first MultiGrade engine oil. This oil has additives that keeps the viscosity of oil almost constant, even when temperature changes. This oil changed everything, pun intended. Now a vehicle only needed one type of oil, no matter the weather.

Interpreting Grades. The Society of Automotive Engineering (SAE) came up with the numerical system for grading motor oil viscosity. Let’s use an oil graded SAE 5w-30 as an example. Remember, the lower number means oil is thinner at low (winter) conditions. The 30 is the rating for how well it performs at high temperatures.

What’s Your Grade? Your engine manufacturer will have a recommendation about what grade oil is best for your vehicle. This might vary if you live in the frigid northern Minnesota or the boiling southern Arizona desert. Since the weather is pretty temperate here in North Carolina, you’re usually fine sticking with what the owner’s manual said.

Of course you can also just ask us. At Norris Automotive, we change a lot of oil, and have seen just about every different scenario. So whether you need 0w-30 or 10w-40, we promise that we’ll give you Grade A service no matter what the season – or the temperature.

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