Oil

[alp231]

Will oil go off in container? I have about 3 liters in a container that's been opened lid on been there for about 2 years just wondering if it's useable

[MrGrumpy]

I'd guess so. Petrol is useless after a year or so.

[smeghead]

I looked into this as I’ve also got some that was opened a few years ago and I need to do an oil change on the Vespa. I read that oil lasts 5 years if unopened but only about a year if opened. So much for buying far more than you need eh!

[Sylar]

I would think it would depend on, if it was, mineral, semi synthetic or fully synthetic.

[alp231]

Semi synthetic.
Oil seems expensive at moment but probably not worth risking

[Data]

Yes, as said by the guys it does "go off". Surprisingly, the type of oil it is ie: dino, semi syn or fully syn only makes a small difference to how long it lasts. Smeg is pretty much right, new sealed tins or bottles of fully syn will last 5 yrs. While semi syn is usually 4 yrs & dino (mineral oil) can vary a bit more but is usually 3-4 yrs. However, once any oil is opened but resealed with the cap on tight, it has just two yrs of life left. Few oils will last longer & some won't even last 2 yrs.

Folks ask why oil deteriorates in the tin? The answer is simple. The additives start breaking down almost as soon as the tin is sealed at the factory. Some additives actually turn to water over time in the tin while others return to their natural state. Opening a sealed can & letting the air & some moisture in just accelerates the process vastly. This contaminates the base oil or oils sparking other reactions. If you are not sure about the age of your oil, there is a code on the can that will tell you its age. Although in some cases you may have to visit the manufacturer's website to decipher the code.

[roadster]

Unfortunately these types of on-line discussion are a bit thin on facts and in my opinion should be taken with a pinch of salt. No particular criticism of any one post but just as examples:-
Which additives turn to water ,in what quantity, what harm would that amount of water do?
If opening the container allows further contamination how much of the contaminant is introduced in the amount of air which potentially fills space previously occupied by oil given that the container is re-sealed after use?
Compared to the deterioration of the oil once it is in use in an engine, where it is typically regarded as OK for 12 months of use, what qualities does it lose when in the original container?

Its very hard to get honest information from companies that want to sell more oil, and the internet is notorious for repeating conventional wisdom which can sometimes be baseless or exaggerated. But if your concerned then perhaps you should use old oil in the lawn mower; that's what I do!

[Data]

Yes, all very realistic questions! You are a man after my own heart roadster. But I think you are asking the wrong questions!

In the motor engineering science community this subject is well known about. Techs are also pretty well versed in it. But generally speaking much of the motoring public know very little about the oil subject and the things about it that matter. But then, why would they? Most don't realise that 80% of oil sold is mostly organic and like any organic substance (petrol included) it goes off & therefore has a use by date just like food. Even highly refined fully syn oil degrades over time, although it is more stable for longer due to a lack of organics. It must be stressed that it doesn't matter how tightly you put the cap back on the oil, water will be present as the oil deteriorates. Actual amounts of water may be quite small though.

But the question of water developing in the oil whilst being stored isn't really the main issue. It's the fact that the additive/s that turned to water are no longer present in the oil in the amount required to meet the oil specification. Other additives also deteriorate, changing their characteristics. If out of date oil is used any water present in the oil will of course just burn off, evaporate once added to an engine. This can leave small amounts of contaminants behind that can act as a catalyst for further degradation. So the overall spec of the oil can be considerably changed if the oil is out of date. By how much will depend on the type of oil, it's spec, the storage conditions especially temperature & humidity & by how much out of date the oil is. A standard oil test will often show any deficiencies.

Of course once in the engine oil degrades even more quickly. It's squeezed, hammered, shredded, virtually boiled, has massive amounts of water added to it from the combustion process, some of which turns to acid when mixed with carbon, dirt & unburned fuel. So it's no wonder a once a year or sooner oil change is required.

When I worked in engine design & development, over the years I worked closely with Tribologists from several oil companies. It was the oil companies that carried out lots of engine testing at that time alongside us techs & developers. It was amazing what those guys knew, & not just about oil. Their engineering expertise matched the highest engineering qualifications. For me it was great to learn the finer points about oil. It certainly helped in every aspect of my job. By the way, it's a great idea using up your slightly out of date oil in the mower. We all do that I hope!

[DTO]

I think everyone has a 30 year old can of duckhams hypergrade in the garage somewhere

Trouble is most times a 4 litre bottle is cheaper then buying 3x1 litre bottles , These would last my Vespa for 2 annual oil changes .

[capitano]

By the way, it's a great idea using up your slightly out of date oil in the mower. We all do that I hope!

I use up mine, and oil from clients who've given up driving as chain lube for two chain driven motorbikes and a collection of bicycles, plus in oil cans as general lube for everything from my garden gate to the deadlocks on my van.

My mix up of out-of-date 10W40, 20W50 etc probably isn't the very best stuff for all purposes, but it does me handsomely.