I'm new at this, so bear with me.
I have several vehicles personally and in my company. Many times we exceed our oil drain schedule (10k) many times with no ill affect. I would say our equipment is under the extreme duty catagory and are driven every day. I have yet to have a mileage oil change issue with any one of them regardless of brand. Our highest mileage was with a Chevy V6 at 189,000 hard miles still going strong.
We had a 2002 Chevy Blazer (with 61,000 miles)setting for a year and the oil (Delo 400)only had 300 miles on it. When we started it (several times over several days) we had lifter rattle.The lifter would pump up but rattle again at start up. A quick oil change solved the problem. We have now driven it 1,000 mile with no undue noise.
I have alway heard of oil breaking down with time but this is the first time we have seen it.
We have changed to a Full Synthetic for any that may set for a long length of time. Don't know the outcome with the synthetic as of yet.
Sounds that many of you have much better technical info than I. Maybe you can make an evaluation concerning oil changes and time frames.
Hope this helps someone.
Original Post