There is a great deal of debate over the use of synthetic oils. Generally, those people who regularly use synthetic oils regularly swear by them, and those who use conventional oils swear by them. For most driving conditions, if you use a conventional oil and change it at the proper intervals, it will properly protect your engine. If your vehicle is subject to extreme conditions, such as sustained high speeds or high loads, extremely dusty conditions, racing, towing, use of a turbocharger, etc., the use of a conventional oil may not adequately protect your engine. The key is to use the proper oil change interval for your situation. Synthetic oils claim to allow a longer interval between changes. This claim is countered by those who point out that regardless of the condition of the oil, contamination from outside sources such as blow-by and moisture cannot be removed by filtering, and regardless of the lubricating properties of the oil, when contamination reaches unacceptable conditions, the oil and filter should be changed.
The main attractions of synthetic oil are its improved lubricating properties and extended oil change intervals. The trade-off for this is cost. Synthetic oils can cost as much as 4-5 times more than conventional oils. This cost increase can nullify the savings gained by the increased change intervals.
Another factor to consider is overall maintenance. If you have a repair facility doing your conventional oil changes for you every 3,000 miles, a trained technician is inspecting your car for potential problems. Your mechanic will be checking things like fluid levels, belts, hoses, tire wear patterns, under-car oil or transmission fluid leaks and other items that can help prevent breakdowns or expensive repairs. For example, replacing a weak coolant hose can prevent having that hose burst in traffic, with resultant overheating and engine damage. This type of preventive maintenance can greatly extend the life of your car. If you use a synthetic oil and only change it every 10,000 miles or more, then you are not getting your car inspected by that mechanic anywhere near as frequently, and problems may be more likely to develop between inspections.
If you are doing your own oil changes, then you need to be aware of these types of inspections and perform them yourself. If you do these inspections regularly every 3,000 miles, then you can possibly extend your oil change intervals by using a synthetic oil; however, keep in mind the problem of moisture and blow-by contamination.
Synthetic oils do lubricate better. However, given the high quality of today's conventional oils, the high cost of synthetic oils, and the other factors involved in determining oil change intervals (and therefore cost-per-mile), there may not be an advantage in using synthetic oils for normal operation. If you are putting a lot of stress on your oil, however, you might consider a change to synthetic oil and staying with a short change interval. This will provide the protection of synthetic oil, although your costs will increase. Those costs should be balanced against the possible cost of premature engine repairs due to excessive wear from harsh operating conditions.
There is no easy answer to the question of conventional vs. synthetic oils. The answer depends on your driving, your maintenance, and your personal preferences. Generally though, if your vehicle is subject to extreme conditions, synthetic oils might well be worth looking at