Follow the Money
Unfortunately, there are market forces that have a vested interest in convincing vehicle owners to change their oil more often than necessary. The legal prey of these market forces have become convinced that they are purchasing "cheap insurance" or "peace of mind" by changing their oil more often than necessary. Complicating things is the fact that doing oil changes is one of the few do-it-yourself maintenance tasks that is still within the ability of the backyard mechanic to perform.

Recreational Oil Changing
The term "recreational oil changer" was coined to define people that change their oil far more than necessary because they actually enjoy doing it. It's easy to understand the psychology behind the recreational oil changing. It's the visceral feel of the tools, the victory when that old oil filter breaks free, the hot dirty oil pouring out, the joy of oiling of the gasket on the new filter, that new copper or fiber gasket on the drain plug, the clean clear oil going in, and the sense of accomplishment when you start the car, the oil light comes on for a moment, then goes out. For $8-10 in oil and parts, it's pretty cheap entertainment, but if people would be content to do it only when it provides some benefit to the vehicle it would be better.

The 3000 Mile Myth
The 3000 mile oil change interval has been pounded into people's heads for decades. It had a scientific basis when engines used non-multi-weight, non-detergent oil. It no longer has any scientific basis, but it is still being promoted by certain entities, most notably the oil change industry in the United States. This myth is also sometimes known as the "Cheap Insurance Myth."

The 3000 Mile Fact
There are still vehicles that need 3K oil changes, but it's not because the oil goes bad after 3K miles. One example is the Saturn S series. These vehicles have a timing chain system that is very sensitive to clean oil because oil pressure is used as hydraulic fluid to ratchet up the timing chain tensioner. If varnish forms in the timing chain tensioner bore then this system can fail and the chain will become loose and eventually break. Dealers have gone as far as tearing out the normal service schedule (6000 miles) and leaving only the severe service schedule. If your engine is destroyed (under warranty) by a failed timing chain then the dealer will legitimately request evidence of oil changes. Unfortunately this problem usually won't manifest itself during the warranty period.

Summary

1. Don't fall for the 3000 mile myth or the dark oil myth

2. Follow the manufacturer's recommended change interval for severe service or have an oil analysis performed to see if you can use the normal service interval

3. If you do the oil changes yourself then buy the oil and filters near the date of the oil change and keep a maintenance log with receipts

4. Use an API certified 5W30 or 10W30 oil (whatever your manual says is preferred) and watch out for oil change places that force 10W30 on you

5. Don't use oil additives

6. If you really want to know the optimum time to change your oil than have oil analyses performed

7. Use the manufacturer filter or a quality after-market filter (don't go by brand name recognition!)

8. Synthetic oil is a good choice if you have a high performance engine or if you live in an extremely cold climate, otherwise it provides no benefit (but no harm either).

9. Avoid engine flushes

10. Check your oil