Motor Oil Basics

By Stephen Bucaro

Without motor oil, your engine would run for only a few minutes before it seized up and was damaged beyond repair. Motor oil is required to lubricate the moving parts, like the crankshaft bearings and piston rings, inside an internal combustion engine. Motor oil also helps in cooling the engine.

Motor oils are made from the heavier distilates derived from the refinement of crude oil. Modern motor oils contain additives that prevent it from breaking down and developing into sluge. Other additives modify the oils viscocity. Detergents are added to clean soot particles from internal engine parts.

The specifications of motor oil are required by the American Petroleum Institute (API) to be displayed in a circular label on the back of the container. At the top of the label you'll see the text "API Service" followed by two or more letters indicating the service that that the oil was designed for. Codes beginning with "S" are designed for engines with spark ignition. SJ is only for 2001 and older engines. SL is only for 2004 and older engines. SM is for all engines.

Codes beginning with "C" are designed for compression engines (diesel). These codes designate the oils ability to meet exhaust emission standards. CG-4 meets 1994 emission standards. CI-4 meets 2004 emission standards. CJ-4 meets 2007 emission standards. You can also use CJ-4 oil in older diesel engines because it exceeds the emission standards for those engines.

Next to the service code, or elsewhere on the container you may find the oils ILSAC specification. This is an indication that the oil was designed with energy conserving qualities.

In the center of the label is the viscosity of the oil. Viscosity is a measure of the oils thickness. 5 would be a very thin oil. 50 would be a very thick oil. After the first number in the viscosity you wil most likely see a "W". This means the oil is "multi-weight". The number following the W then becomes the viscosity of the oil under normal operating temperatures, while the number to the left of the W (which stands for "winter") is the viscosity of the oil in cold weather.

If you live in a part of the country that has cold weather you'll want an oil with low viscosity so that you can get the engine cranked over in winter. If you live in a part of the country that has hot weather, you'll want an oil with high viscosity to protect the engine. Multi-weight oils allow you to choose one oil that will vary its viscosity with temperature. If you live the south west U.S. where you never have cold weather, you don't strickly need multi-weight oil, but "straight-weight" oil may be difficult to find.

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