Oil change interval, why is there a time limit?

Change in viscosity is the key.

T18skyguy wrote:
This is what I've read on the longevity of oil in the pan by date. The oil slowly combines with oxygen, and results in oxidation, which leads to sludge/coke or whatever other bad things. The filter media can also be attacked and ruined by the acids in oil while it sits in the filter. Then there is also the steady addition of water to the oil. This happens even when the engine is not running. The air in the engine is the same as outside, so when it hits the dew point, it condenses inside the engine, makes rust if it can, then settles into the pan. That water burns off if you run it, but not if it's parked for long periods. At night the engine inhales when the air gets cool(contraction), and when the day warms up it exhales(expansion), kinda like we do. I do the Mobil 1 annual oil once a year.

This answer makes a lot of sense to me! Thanks for the post.
Brian

There are chemical additives in the oil, over time they break down once they are exposed to the hazards of a running engine. Thus the Time Limit.

Those that change every year probably change their cars every 3000 miles. That was debunked 40+ years ago by Consumer Reporter in Checker Cabs. About the same time oil analysis let me go 250 hours instead of the Cat recommendation of 100.

This is what I've read on the longevity of oil in the pan by date. The oil slowly combines with oxygen, and results in oxidation, which leads to sludge/coke or whatever other bad things. The filter media can also be attacked and ruined by the acids in oil while it sits in the filter. Then there is also the steady addition of water to the oil. This happens even when the engine is not running. The air in the engine is the same as outside, so when it hits the dew point, it condenses inside the engine, makes rust if it can, then settles into the pan. That water burns off if you run it, but not if it's parked for long periods. At night the engine inhales when the air gets cool(contraction), and when the day warms up it exhales(expansion), kinda like we do. I do the Mobil 1 annual oil once a year.

"supercub"....Living where you do, you'll be fine going two years on a oil change.

You spend 100K plus for a DP or 70K for a diesel truck and worry about a couple hundred for oil? There is no maintenance you will do that will make it last longer than clean oil & filters. Two diesel P/U's changed once a year 1 210K the other 163K never need apart. Class 8 750K changed MONTHLY @10-12K per, replaced 1 injector. An oil change & filter change a year is peanuts.

rgatijnet1 wrote:
All it takes is to spend a few bucks for an oil analysis. That will tell you if your oil still has any life left in it and will help you make an informed decision in the future.

X2

I use Blackstone Labs

As long as you drive it and put it away hot I change on miles only.
Time limit is for the semi-weekly 1/2 mile run to the grocery.

Still unsure? Get the oil analysis.

Have you every seen an expiration date on a jug of oil like there is on a jug of milk?

I would probably feel a lot better if the oil hadn't been in the engine for five years, but I don't worry about one year. I wonder how many years the vehicle mfgs have been copying and pasting that paragraph? Probably from long before there were computers used to cut and paste with.

Bill