On most of my vehicles I do once a year because I only put 3-4,000 miles on during this time. My everyday driver, a 92 chevy cavalier with the 2.2L, I usually go every 3-4,000 miles. I have a 60 mile round trip drive to work every day so I'm changing about every three months. The recommendation for this car for highway driving is actually every 7,500 miles but I have never gone this long. 5,000 miles has been the longest. I use conventional Valvoline in all of my vehicles.
Wayne