What Is Viscosity?
When you're shopping for motor oil or looking through your owner's manual for your car's recommended oil type, you may notice the word "viscosity" being thrown around a lot. It's a word that's often associated with a series of numbers and letters, like 10W-40, 5W-30, and SAE 30. Read on to find out the meaning of viscosity as it relates to engine oil.
The Definition of Viscosity
Viscosity refers to how thick or thin a liquid is. It’s measured by timing how fast a liquid flows out of an opening in a container. The thicker an oil, the slower it will flow (and the higher viscosity it will have). The thinner an oil, the faster it will flow (and the lower viscosity it will have). Motor oil will become thinner as it heats up and thicker as it cools down, just like maple syrup!
What's A Viscosity Grade?
All motor oils are given a viscosity number, or grade, by the Society of Automotive Engineers (SAE). An oil's viscosity grade helps drivers determine how thin or thick a motor is (and will be) under certain conditions. As noted above, this grade looks similar to 10W-40, 5W-30, and SAE 30, but there are many more viscosity grades as well.
How Do You Read Viscosity Grades?
Let's use 10W-40 as an example. The number in front of the W stands for Winter and is the oil's resistance to flow at 0℉. The number after the small dash is the oil's resistance to flow (or thickness) at 212℉. Talk about hot! In general, thicker oil seals better and maintains better lubrication between the engine's moving parts.
Before grabbing any old motor oil off the shelf, consult your owner's manual, as it will indicate the advised viscosity grade for your car's engine. Or, stop by your nearest Firestone Complete Auto Care location and talk to one of our ASE-certified technicians. Any one of them can answer the question, "What is viscosity?"
