For maximum protection, most oil companies say to change the oil every 3,000 miles or three to six months regardless of what type of driving you do.
A new engine with little or no wear can probably get by on 7,500 mile oil changes. But as an engine accumulates miles, it dumps more unburned fuel into the crankcase which dilutes the oil. This causes the oil to break down. So if the oil isn’t changed often enough, you can end up with accelerated wear and all the engine problems that come with it (loss of performance and fuel economy, and increased emissions and oil consumption).
Regular oil changes as part of preventative maintenance are cheap insurance against engine wear, and will always save you money in the long run if you keep a car for more than three or four years.
WHAT ABOUT THE OIL FILTER ?
To reduce the costs of vehicle ownership and maintenance, many car makers say the oil filter only needs to be replaced at every other oil change. Most mechanics will tell you this is false economy.
The oil filters on most engines today have been downsized to save weight, cost and space. The “standard” quart-sized filter that was once common on most engines, has been replaced by a pint-sized (or smaller) filter. You don’t have to be a rocket scientist to figure out that a smaller filter has less total filtering capacity. Even so, the little filters should be adequate for a 3,000 mile oil change intervals but may run out of capacity long before a second oil change at 6,000 or 15,000 miles. Replacing the oil filter every time the oil is changed, therefore, is highly recommended by professional auto mechanics.