Your car's engine oil serves several crucial functions. Most importantly, it's a lubricant of the many internal parts of the engine. Oil also helps to collect and disperse heat generated by moving parts. Small particles formed from engine wear and tear are also flushed away by the oil as it travels through the engine, and are trapped in the oil filter. To be sure your car will last as long as possible, it's important to change the oil at regular intervals. Many mechanics recommend changing the oil at least every 3-thousand to 35-hundred miles. If most of your trips are on the highway instead of driving in the city, you may be able to stretch the oil change interval to around 75-hundred miles. You should make sure the oil filter's changed every time your oil's changed. Otherwise clean oil will flow through a dirty filter. The reason you must change the oil in your car regularly is because of additive breakdown. Over time, several of the important engine protectants in motor oil will dissipate, leaving your engine vulnerable to damage.