Interesting. I need to start doing the oil analysis thing. I've got some 20w50 laying around for the nova that's about 10 years old. It now looks like bar and chain oil...

 

Do you guys do interval oil changes if you go long periods of time without reaching a mileage milestone?

 

Yes, you should. The problem is that the additives will break down even if you don't hit the mileage milestone. In cars that are run short distances additives can be neutralized, depending on how often you drive the car, in a year even if you only drove 1000 miles. The reason is that if you don't get the car hot, and hot for enough time, then gasoline and other contaminants cannot burn off the oil which causes the additives that neutralize acid and that suspend particles to become "neutralized" or "used up" in less miles then a car that is used to drive longer distances. If you have a car that you start once a month and let get to operating temperature, or that you don't start at all, you could probably leave the same oil in for two years before the additives were neutralized.

*Disclaimer* - If you have a car sit for two years without running it you will probably have more problems to worry about other than whether your oil is good or not.

 

I never hit the mileage milestones. I just follow the Oil life indicator and everything seems to be fine. I drive maybe round trip 10 miles to work and back. My oil is basically changed every 11+ months.

My rule of thumb is to change the oil when I am <30% oil life. If im low on cash flow i'll let it go to <20% before I change it.

Have 95,000 miles on the car now and no mechanical issues. Also not I never hit the mileage milestones before I change the oil either so Im still following your guidance.

 

I change at 30% or 5,000 miles whichever comes first. If it sees a lot of racing action I change at closer to 4,000 miles. Oil costs less than bearings.