Engine Oil Weights and Viscosity

Typically, among of the more common questions that people have in regards to basic automotive care is about engine oil weights and viscosity. These questions usually center on the general idea of what the terms engine oil weights and viscosity mean. Here is the definition of these terms, as well as a brief tutorial on how to interpret the information that is on the side of most oilcans found in department and automotive stores around the country.

I always like to start with the basics, and in this case the basics would be the definition of the two terms engine oil weight and viscosity are. The definitions of these two words, weight and viscosity, in this specific case are the same thing. In the case of automotive oil these terms are talking about the thickness of the oil in question.

Most engine oil used today is multi-grade oil, which means that the substance is designed to operate in a variety of different situations. You can tell the situations by looking at the Society of Automotive Engineers (SAE) classification that is on the side of all motor oil products. Don't worry if you are a little confused by the phrase SAE classification, since you already know what this is, but you already know what this is whether you realize it or not. This classification is what most people refer to when they say "10 weight" or "30 weight." This is actually referring to the classification on the side of the bottle or can that read 10W40.

In the case that I showed above, the 10W40 is what is known as the SAE oil viscosity grade. Let's take a look at what this basic designation actually means, so that we can understand what is getting put into our car engines a little better. Whenever you see something along the lines of the example that I gave here, it is what is known as a multi-grade oil. I am going to explain this, since this is the type of oil that most people, and manufacturers, put into their vehicles.

The W that is used in such multi-grade oil labels does not refer to the oil's weight (or viscosity) directly, but in actuality it is referring to winter, and the oil's viscosity during the colder times of the year. This is part of the testing that the SAE has set up to determine the performance of petroleum products during cold weather operation, while also protecting the engine from operating at higher engine temperatures and loads. If you are in an area of the country, or world, that has a warmer climate on average, then you can probably use a single-grade oil as opposed to the multi-grade.