KEEP YOUR ENGINE RUNNING SMOOTHLY

                   Changing your engine oil as recommended by your vehicle's manufacturer is one of the least expensive ways of keeping your car in god working order for many years.
                    In addition to keeping your vehicle's moving parts well lubricated, engine oil helps draw heat away from the combustion chamber and prevents carbon and varnishes from accumulating in the engine parts.

Oil by the numbers
                    Your owner's manual will denote the proper viscosity (thickness) of oil your engine needs.  You also may be able to find the information printed on the oil cap under the hood.  Engine oil comes in several different viscosities, such as 10W-30, 20W-50, 15W-40, SAE 40 and 5W-30.  The numbers represent oil thickness as measured by the Society of Automotive Engineers (SAE) during hot and cold testing, wrote Joe Bruzek of automotive website http://www.cars.com/. 
                   "For 10W-30, the first number (10) is the oil's viscosity when cold; 10 weight is thinner than 30 weight and beneficial when cold, because thinner engine oil allows easy start-up and less strain on the engine," Bruzek wrote in his article "Choosing the Right Engine Oil."
                    The second number (30 in the above-noted case) is the oil's viscosity when it's warm and is typically a heavier oil, thus providing better protection at higher temperatures, Bruzek continued.  And the 'W' paired (as in 10W) designates an oil certified by SAE for low-temperature use in winter.
                   It's important that you use the manufacturer's recommended oil, Bruzek noted.  If you don't you may void your car's warrenty if any damages can be shown to have been caused by your use of the wrong engine oil.  Other ways to void your warrenty include:
     * using a heavy oil weight, like 20W-50, in a car that recommends 5W-30;
     * using a synthetic oil that's not approved by the automaker;
     * using oil that's not approved by the American Petroleum Institute (API) in a car that requires API certification (look for the API starburst on the oil container).
                  API certifies oil based on performance criteria that have been determined by oil and engine producers and automakers, noted Mike Hanley of Cars.com in his article "Why Oil Matters."  The highest API oil category for gas engines is SM.  "It's designed for all gas engines, and according to the API, oils with this rating offer improved oxidation resistance, improved deposit protection, better wear protection, and better low-temperature performance over the life of the oil," wrote Hanley.
                  Other gas-engine categories in use include SL, which is designed for engines built in 2004 and ealier, and SJ, which is for 2001 and older models.
                   Avoid off-brand motor oils that tout the API's SA category, Hanley wrote.  "This is an obsolete designation that shouldn't be used in cars built after 1930.  There are no specifications for SA oil, so there's no way to know what's in it.

Synthetic oils
                  Some new cars come from the manufacturers with synthetic oils.  These man-made oils can handle extreme hot and cold temperatures better than convential, natural oils.  "Natural oils break down faster during high-heat operation like towing, racing or any heavy-load operation, partly because of impurities that can't be removed in the refining process," wrote Bruzek.
                  Sythetic oils tends to be more expensive than conventional oil, and manufacturers claim you can change your oil less frequently when using their oils.  That said, many automakers recommend you stick to their original time-frames for oil changes, even when using synethic oils.

How often to change your oil
                   As noted, your automaker will denote its recommendation on when to change your oil.  The most common interval is 3,000 miles or three months, with mileage being the more important of the two parameters.
                   Keep in mind, however, that where and how you drive also can influence how often you change your oil.  Extreme heat, driving amidst dust and sand, or towing a trailer all can tax your engine, necessitating more frequent oil changes.  And note that the average car takes four to five quarts of oil during a change.
                   If you don't change your oil on a regular basis and as needed, you're likely to get carbon buildups in and around the cooler parts of your engine, such as the crankcase, stated Hanley.  Other potential problems include worn out piston rings and damaged camshafts.  "Getting a bill for either one of these repairs would make even a few high-quality oil changes look like pocket change," wrote Hanley.
                  In short, think of regular oil changes as a form of inexpensive insurance to keep your engine running smoothly.