Time and mileage intervals vary by vehicle manufacturer and whether an engine requires synthetic oil (which should last longer). Use the guidelines in your owner’s manual, including whether most of your driving qualifies as happening in “severe” conditions, such as frequent short trips and stop-and-go driving. Under those conditions, you should change the oil more frequently. Many mechanics argue that some manufacturers’ recommended intervals of 7,500-10,000 miles are too long and will accelerate engine wear. They say it’s better to change the oil more often than necessary than not often enough.