I saw this post on the Reddit labeled version of Cartalk. The post;
Engineer here for a major automotive company. An older colleague passed along this oil life rule of thumb before he retired. It’s too good not to share. He had reviewed over his career probably thousands of sets of oil analysis data, and this RoT is based on that.
Oil life in miles = 50 * (Engine oil capacity in qts.) * average mpg over the period
So for my Mustang that is 50 * 8 quarts * 19 mpg = 7600 miles
My truck would be 50 * 6qts * 13mpg = 3900 miles
This formula accounts for the highway driver or short trip driver. Highway mpgs are higher so oil life would be longer, the short tripper would have much lower mpgs so the oil life would be shorter. Supposedly the formula is based on acid buildup in the oil so it doesn’t matter if this is synthetic, a blend or conventional oil.
The oil minder on the Chevy seems to trigger much later if driven lots of highway miles but only a little later for short trips. The Mustang is an anomaly as it gets the oil changed early because it gets tracked.