Time vs. Mileage
The time limit against using the same oil is equally as binding as the mileage constraint. Even if your oil looks new and appears relatively clean (gold or brown in color), it should still be changed at the appropriate interval since 1) important additives in the oil become ineffective through evaporation and chemical reaction 2) microscopic particles of dust, dirt, or metal pass through the oil filter and accumulate in the oil, and 3) the oil becomes diluted and contaminated by combustion byproducts.
NEW ENGINE OILOil deteriorates chemically regardless of whether or not it is used. Hot oil oxidizes, a process which breaks down the oil chemically and permits water, generated by combustion, to dilute the oil. Sulfur contained in the oil reacts with the water to form sulfuric acid, which can damage lubricating surfaces. Furthermore, water buildup in the oil can cause sludge.
Furthermore, the oil must be changed regularly to comply with vehicle warranties. The basic idea is to change the oil immediately prior to the deterioration of additive performance. This permits contaminants to remain suspended rather than coagulate as deposits. After a certain "dump-out" point is reached, the oil cannot perform this function anymore. It is better to change the oil a little too often than not enough. You should error on the more frequent side if necessary.
FREQUENT OIL CHANGES USING A HIGH QUALITY OIL AND EFFICIENT OIL FILTER ARE THE SINGLE MOST IMPORTANT MAINTENANCE ACTIVITIES THAT WILL EXTEND YOUR ENGINE'S LIFE, MAXIMIZE PERFORMANCE AND MINIMIZE THE NEED FOR COSTLY REPAIRS.
SYSTEMS
ENGINE OIL
DON'T DELAY
SUGGESTED OIL CHANGE INTERVALS