Oil change time intervals rely on a number of mitigating factors that determine when one should get their vehicle's oil changed. It seems like every person you ask has a different answer for how often engine oil should be changed. Knowing which factors affect the cleanliness of your oil can help you make an informed choice as to when you'll need to get around to changing it.
Where To Start
A good jumping off point would be to look at your owner's manual, which will probably supply a number between 5,000 and 7,500 miles. The manufacturer actually built the car, and as such should be viewed as the highest order when it comes to maintenance advice. Though, manufacturer recommendations are based on ideal driving conditions - driving short distances, never over the speed limit, that kind of thing - something the average driver would be hard-pressed to accomplish. As such, you’re better off using the “severe conditions” maintenance schedule, which will have you changing your oil roughly every 3,000 miles.
What Affects Oil Change Intervals
So, once you've uncovered the carmaker's estimated oil change mileage, there are a few issues that need to be reviewed to adjust that estimate. Hard driving is a major wear and tear factor in determining the mileage amount for an oil change. If you're driving in a lot in extreme conditions (both hot and cold), stop-and-go traffic, towing a trailer or hanging out on dusty roads, you must change your oil more frequently.
Conversely, and perhaps obviously, if you're not driving very much, you'll be able to get away with longer periods in between oil changes. This is a situation when you wouldn't need to change your oil as regularly and could stick closer to the manufacturer's suggestion. But remember, it is good to change the 'black gold' in your car even if you don't drive it that much, and when you do so we also recommend a high-quality oil filter, as this is every bit as important as the quality of oil itself.
If your car has been around the block a couple of times, oil changes should be at increasingly more frequent intervals compared to how often you changed it when your car was new. This is due to "blowby": compressed fuel and air that has leaked into the engine's crankcase. Over time, soot and grime builds up on the rings, making them slightly permeable and resulting in contaminated oil that needs to be changed more regularly. Synthetic oil is recommended for longer engine life and better engine performance.
Though having to only change your oil every 7,500 miles is something we would all prefer, 3,000 to 5,000 miles are numbers more representative of actual driving conditions. By erring on the side of caution, you'll help to extend the life of your car.