What Matters When Picking Oil? Pt. I

Motor Oil being poured into a container.

Buying oil used to be simple – find what oil you need, go to the parts store and buy it. Today, things are a bit tricky. The walls of oil at parts stores are about as big as the grocery section at your favorite store.  Different weights, different brands, different blends, different lengths of time until it needs to be changed… so what oil is “right?” To answer that, we first have to dive into some of the science of oil.

Traditionally, oil came as a singular weight.  The Society of Automotive Engineers determined how thick an oil was by running it through tubes and seeing how long it took to pass through.  For example, an SAE 30 oil takes about 30 seconds to flow through the SAE’s tube-test. You generally bought a heavier weight oil, like a 30, in the summer and something less thick in the winter, like a 5.

Modern oil is what is called a Non-Newtonian Fluid. That means that motor oil doesn’t follow Newton’s Law of Viscosity – the idea that a fluid does not change it’s “thickness.” Modern oils can act differently depending on the conditions, that’s why oils are labeled with two weights.  Take for example 5W-30.  In “winter” conditions the oil will handle like an SAE 5, while in warm conditions it will handle like an SAE 30.

We’ll continue this next week! Any questions? Feel free to call Manchester Auto and Tire of Mint Hill, LLC at 704-545-4597, email us at kenmanchester1@gmail.com, or message us on Facebook at facebook.com/ManchesterAutoandTireOfMintHill