Why do I have to do regular oil change?

Oil undergoes thermal breakdown due to high operating temperature. When this occurs, the oil becomes less effective as a lubricant. And without a good lubricant , parts of the engine rub together and wear each other out.

The repair facility gets a chance to do a 14 point safety inspection. Check belts, hoses, tires, brakes, lights, for wear and or damage, coolant and other fluid levels for leaks.

Oil also contains additives that have the ability to neutralize acids. Over time, these additives get used up and stop being effective.

Finally, oil can absorb water, dust and combustion byproducts and also hold them in suspension. Eventually, the oil gets saturated with this stuff and can´t absorb any more. Then that stuff remains in the engine and can cause corrosion.

Is there any maintenance required between intervals?
Yes, you need to check the oil level every few hundred miles. With your car parked on a level surface, remove the oil dipstick, clean it on your brother's best shirt and then reinsert it. Remove it again, and check the oil level.

Ideally, it should be right at the “full” mark. If it´s at or below the “add” mark, that means you´re a quart low and should add a quart of oil to the crankcase. If it´s in between the two marks, you can add part of a quart to bring it up to the full mark (the distance between “add” and “full” represents a quart, so use that to estimate how much of a quart you need).