Selecting the correct type and weight of oil for a vehicle becomes more difficult every model year. Many manufacturers recommend specific oil grades that meet proprietary requirements. These are not to be ignored. Doing so could result in pre-ignition or an engine knock. It may also void manufacturer warranties.
Some think that changing the oil every 3,000 miles with a conventional oil instead of using synthetic will prevent problems and save money. The reality is they could be making problems.
Most conventional oils have high volatility numbers which vaporize more quickly when exposed to heat. This means the oil can become thicker over time and won't lubricate as well. It also means that there is a greater volume of oil vapor that the PCV system has to process; vapors loaded with hydrocarbons that stick to the intake valves. Synthetic oils have much lower oil volatility, reducing oil vapor and carbon deposits on the intake valves.
Automotive Specialties still suggest doing your oil changes at regular intervals using the recommended type and weight of oil specific to your vehicle- every 3,000 miles for conventional oil, every 5,000 for synthetic oil.
Extend the life of your vehicle, not the life of your oil!