Well that's the same problem with me,l have lots of compounds some l bought 20 years ago, but still liquid and all paints, what about oil expiry dates, normally on side of can if expired to use or not to use, l have a couple of 10-40 l would like to use but not sure about date, it's expired.
This source says that the date printed on the side of the jug or bottle of oil is NOT an expiration date, it's the manufacture date.
https://www.blauparts.com/blog/motor-oil-expiration-shelf-life.htmlTechnically, there is no "expiration date" for lubricants that I'm aware of. Only "manufacturers recommendations". If you have information otherwise, please share.
I know that some manufacturers have recommended 5 years as the shelf life of their products, but I'm pretty skeptical. Especially if we are talking about dino oil, that stuff was 50,000 years old when it went into the bottle. If it has been kept away from heat and oxygen, in a sealed bottle, it doesn't seem likely to change its properties much in another 50 years. I know that polyethylene is semi-permeable, but the amount of oxygen making its way through the bottle, especially if there is a cap layer, seems negligible. Oil companies want to sell oil, they are all in favor of having you buy more, for whatever reason. This company wants you buy more of their stuff after just two years:
https://www.lubricants.total.com/does-motor-oil-expireDoes this count the time the oil spends in the carboy before it gets put into the bottle, or the time it spends on a pallet at the warehouse, or the time it spends in back at the store, or the time it spends on the shelf in the store, or is it only the two years on your basement shelf that you need to count? Count ME, very skeptical of these "recommendations".
I can't speak to synthetic, that stuff seems inherently more questionable. Man made vs Nature made.
I'd dump my old oil into a clear container, check for sedimentation and separation, do a finger rub lubricity test, and if everything looked right, I'd use it, for sure. I certainly have, and will continue to, use oil old enough to have been sold in a can that requires a can opener. I should probably put what is left of those on Ebay. They are old enough to be more valuable as movie props.
For reference I also use expired milk. When the milk gets old enough that it curdles in my coffee, I make cheese out of it.