Vehicles have changed more in the last ten years than they did in the previous thirty, and the way they need to be serviced has changed along with them. They are more reliable than ever, and are able to go much longer between service intervals. The most common service a vehicle needs is still an oil change, but the oil change, and the oil, has changed significantly. Most cars and trucks now have computer-based monitoring of oil life. The familiar four times yearly schedule has also changed, with most cars now able to go six months or even a year on the proper oil.
Oils are now engineered alongside an engine as it is developed. The familiar SAE numbers like 5W-30 and 10W-40 are part of an antiquated standard leftover from the 80s. These standards primarily indicate the viscosity of a lubricant at specific temperature ranges, and do not reflect the specific requirements that manufacturers set for their engines as they are developed. Most manufacturers have minimum standards for the oil's reactions to pressure, shear, and temperature. Each manufacturer has its own set of standards, sometimes several standards for its different engine designs.
The computer in your car that reminds you to check your oil does not make any direct measurements of the oil's condition. It infers the condition of the oil based on the type of driving you've been doing since the oil was last changed. The computer assumes that the oil used meets the requirements for which it was programmed. These requirements allow the computer to predict how the oil will respond to your driving habits, and tell you when it needs to be changed.
