My V-6 Park Avenue's OLM would usually still be at 40% life left when I'd change at 6 months/4500-5000 miles, so it would drop about 10% a month. However -- and I know it's way too early to tell anything from this -- the OLM in my 4-cyl. non-turbo Regal, driven the same way over the same routes, in chilly but not sub-freezing weather, has dropped 4% in the last week. This suggests 16% a month. At this rate, if hot weather (which'll be here in six weeks) doesn't make any difference, I'll need to change oil in mid-May.
So if it is the same GM OLM, it seems to be coming up with some different answers for different engines, not just being a mileage counter.
So if it is the same GM OLM, it seems to be coming up with some different answers for different engines, not just being a mileage counter.