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Deciphering Engine Oil

When purchasing replacement oil for your vehicle the story is short and simple, follow the guidelines provided in your owner’s manual for optimal performance. The rest of the information in this article explains some of the differences you will find in the many types of engine oil available on the shelves today.

Engine oil, also known as motor oil has to perform several functions including lubricating moving parts, helping to cool the engine and cleaning dirt and sludge deposits from the engine reducing friction and wear. Because it must do these jobs simultaneously today’s motor oil is made up of a complex chemical formula and should be changed regularly according to the guidelines put forth in your owner’s manual.

Quality oils carry up to three certifications from three different organizations. These certifications indicate that the oil met the testing and content requirements of these organizations. The most well-known is the American Petroleum Institute’s (API) “starburst” and “donut.” The outer ring will say “API SERVICE” followed by two letters, for example “SM”.  “SN” is the most current API Service Category available. If the service rating starts with a “C,” it’s for diesel engines. The second is by ILSAC and works with API with the added requirement of fuel economy.
The third certification was developed by the Society of Automotive engineers to rate the thickness of the oil. It’s expressed by four or five characters, such as 10W-30. The lower the number before the W (for “winter”), the better it flows in cold temperatures. The number after the dash indicates how well the oil flows when it’s warm. Many manufacturers currently specify light oil, such as 5W-20 as some modern engines have incredibly tight clearances between parts. Especially when the engine is cold, heavier oil may not reach into these tight areas.

You will find oils labeled for specific purposes: high-tech engines, new cars, higher-mileage vehicles, heavy-duty/off-road SUV’s, these are made from premium conventional oil, synthetic or a blend of the two.  Premium conventional oil is the standard oil used by most cars and light trucks. Synthetic oils are made for high tech engines, such as corvettes or Mercedes, and have longer-lasting performance in all the critical areas. So why shouldn’t everyone use them? Answer: These oils are expensive and not every engine needs them. Synthetic blends are a mix of both and overall are formulated to provide protection for somewhat heavier loads and high temperatures; they’re also a lot less expensive than full synthetics. Higher mileage oils are formulated with seal conditioners to help reduce small leaks and anti-wear additives to try and slow the wear process.

Finally additives, these are used to assist in maintaining good lubrication, and minimize sludge and varnish. Common additives are detergents, dispersants, anti-wear agents, friction modifiers, antioxidants, foam inhibitors and rust inhibitors.

Don’t be overwhelmed at the prospect of purchasing oil; just remember to look for the certifications and what type of oil your owner’s manual recommends.

Want to know more about how to care for your car properly? Learn more about your car by reading our posts!