Question about engine oil shelf life, once opened how long can we save it before it becomes degraded? Does it absorb moisture over time?
I have some that was opened about 2 years ago and has been sitting with the cap on since.

You ll find that synthetics absorb a lot less moisture, so i guess it depends on type of oil

http://www.machinerylubrication.com/Read/172/lubricant-storage-life


Its titled "Lubricant Storage Life Limits - Industry Needs a Standard " but if you read it you might reasonably conclude that "industry doesn't need a standard", since they don't appear to have one, nor any basis for one.

Like most "pitches", what it doesn't say is as significant as what it does. There is absolutely no evidence reported here for on-shelf deterioration of motor oils. Instead, its served up as a ready-cooked "given" with a side order of "The sky is falling" Chicken-Little panic salad.

Table 4 (recommended shelf life for indoor storage at 20C) is especially instructive
.
Major oil company C: 10-30W Motor Oil (mineral) 1 YEAR
Major oil company C: 10-30W Motor Oil (PAO) 1 YEAR:
Major oil company D: 10-30W Motor Oil (mineral) 1 YEAR
Major oil company D: 10-30W Motor Oil (PAO) 1 YEAR:

Independant oil company B: 10-30W Motor Oil (mineral) Virtually unlimited *
Independant oil company B: 10-30W Motor Oil (PAO) : Virtually unlimited
Independant oil company C: 10-30W Motor Oil (mineral) : Infinite
Independant oil company C: 10-30W Motor Oil (PAO) : Infinite

1 year (!) isn’t very long, and 1 year to infinity is a pretty wide range.

Or "If "Big Oil" says buy new! they make money.

Given that it can be used in your engine for 1 year, I'd say the shelf life is many times that.

Crazy as it sounds the internal combustion process actually produces 'water' as a byproduct. This is one of the many reasons why its best to have an engine do lots of 'lengthy' trips rather then short trips as this 'boils' off the moisture and a lot of the lubrication properties and detergents start working at their peak when up to operating temps.

The oil will be fine to use if left with the cap on.

pretty sure oil lasts a few million years, that is when it was created...

Haha, well I believe that our hi-tech engine oils have many ingredients, all of which must have a shelf life to varying degrees.