Many machines in our daily life require some form of lubrication, often found in the form of a liquid. The most obvious example would be your car's engine which requires somewhere between 4 and 6 quarts of oil to safely operate. This is example is a great learnin' tool, so let's rap.

## Viscosity

The grade, or weight, of an oil is described by a number such as "90 weight". This is actually the oil's viscosity. Viscosity is measured as the amount of time it takes a certain amount of oil to pass through a certain sized orifice at a certain specific temperature. If you want to know those specific numbers, ask SAE. Low numbers like 10 indicate a fast moving and consequently thin oil. High numbers like 90 indicate a very slow moving, thick oil. Long story short: viscosity is quite literally how fast oil moves.

Now, have you ever handled an oil at different temperatures? Think about pouring oil in a cold skillet: how slowly does the oil roll around while you try to coat the bottom of the skillet? What about when you're done cooking and you can pour the oil out like water?

If you have ever changed the oil in your car when the engine was still warm, well. . . I don't have to explain that example at all.

The main idea is that oils become thinner and flow more easily as their temperature increases.

## That's not good!

In your engine, your oil performs four vital functions. It lubricates, seals, cools and cleans your engine. And no, not that kind of cooling--there is a world outside of E2, remember?

It is beyond the scope of this node, but the oil travels through your engine via small passages that measured in the millimeters. If the oil is too thick, the engine cannot move the necessary volume of oil through the passages. Simultaneously, oil forms a protective shield between the pistons and the cylinder walls. That shield measures in the thousandths of an inch. If the oil became too thin and those surfaces came into contact, you could lose the entire engine. Assuming, of course, that you live through the wreck.