- 1). Read the owner's manual to your vehicle. While temperature and climate is one variable to take into consideration when buying engine oil, the second is the manufacturer's recommendation, based on the properties of the engine installed in your car. The owner's manual will also alert you to any specific certifications or properties your engine oil should have.
- 2). Find the two American Petroleum Institute (API) stickers on the bottle. The first resembles a black starburst with a black border, white background and red letters. The second is a white circle with a second white circle inside it.
- 3). Read the outer white circle. After the words "API Service," it will begin with either "S" or "C." "S" oils are compatible with regular automotive engines. "SN" is API's most recent service category rating as of 2011, and backward-compatible with most engines. "SM," "SL" and "SJ" are older category ratings which may not be appropriate for newer engines.
"C" oils are for diesel engines. The most current rating as of 2011 for diesel oils is "CI-4." Older ratings are "CH-4," "CG-4" and "CF-4." Like "S" oils, these older ratings are generally only compatible with older engines.
- 4). Read the second, smaller white circle. Underneath the letters "SAE," it will say something like "5W-20." This tells you the oil weight. The first number reveals how well the oil flows in cold weather. The lower the number, the colder the temperatures it can run in. The second number, after the dash, reveals how well the oil runs in the heat. The higher the number, the higher the temperatures in which it can run.
- 5). Change the oil at least twice a year. If you experience a wide range of temperatures between summer and winter, you may want to change oil in the spring and winter and select a different weight appropriate for the coming temperatures.
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