Oil is the lifeblood of your car. It keeps hardworking engine parts running clean, smooth and cool. Most owner's manuals suggest that you change your oil and oil filter every 7,500 miles (12,070 kilometers). Oil change specialists suggest every 3,000 miles (4,828 kilometers) or three months. The fact is, most of us do a lot of heavy driving during the summer when an engine is more likely to overheat. So at least check your oil before you head out on that road trip with the family.