Easiest and the best thing you can do for your Envoy or any car for that matter is to change oil on a regular basis. I have quite a few cars and have found the easiest way is to keep a record of each auto and when I changed oil when I had service work done. I keep a record of the date and who did the work and of course the mileage. I change oil every 3 thousand miles or sooner depending on your type of driving. Hywy driving you can go a few more miles than city. Stop and go city driving I would change every 1500 to 2000 miles. Any where you read about someone going 2 to 3 hundred thousand miles the first thing they suggest is to check all fluid levels at every gas stop and change your oil on a regular basis. This of course includes the filter.