Have you ever been searching around the back of your garage or in the trunk of your car and found an old bottle of motor oil you forgot all about?
It could be an unopened bottle from that ages-old DIY oil change you were going to perform, or the remnants of a mechanic’s last oil change.
The question you’re now faced with is this: Does motor oil expire? And how can you know if your oil has gone bad?
We all know that oil needs changing at regular change intervals when in the engine, but what about when it’s stored in the bottle?
In this guide, we explain all you need to know about motor oil’s shelf life, including how to identify when it’s gone bad and the difference between conventional and synthetic oils.
Check Before Using – Several quick checks can be used to identify whether or not your oil has expired.
All About Storage – Synthetic oil will last 7 or 8 years on average, but only if stored correctly.
Engine Expiry – Several factors can cause any type of oil to go bad in your engine
Does Motor Oil Degrade?: What the Oil Manufacturers Say
Obviously, the oil companies have a vested interest in the future sales of engine oils—what’s the point of making something that never needs to be replaced?
The general consensus is that motor oil should last for an “extended period” under optimal conditions—in the original unopened container and stored away from extreme temperatures.
The motor oil’s shelf life recommended by each manufacturer varies, though.
For example, Mobil expects industrial or motor oils to last for five years if stored properly in the original container. Meanwhile, Total, another leading manufacturer, says motor oil should be disposed of after only two years if not used.
So, while many motor oil companies shy away from saying their oils do actually expire, they do say we should dispose of old motor oil in a responsible way after a few years. Perhaps it’s those vested interests again!
This also only applies to oils that have remained unopened in their original containers, stored at the correct temperature.
How Does Motor Oil Expire?
The key lies in the manufacturer’s advice on the storage of the motor oil.
Temperature extremities can affect your motor oil, even when unopened. High-temperature extremities may cause thermal breakdown to occur, which reduces motor oil’s viscosity (or its weight and thickness, in layman’s terms).
If this oil is used, it will have a reduced flow rate around the engine, which can lead to an increase in oil consumption, and buildup of debris and damage to your engine.
When motor oil is stored at extremely low temperatures, a sludge may appear, which can block engine passageways. This inevitably becomes too thick to flow easily.
Either form of the oil thickening can result in engine damage that can run thousands of dollars to repair. So, ask yourself the following question: is it really worth saving a few dollars just to use old oil?
What If the Oil Bottle Has Been Opened?
When the original container has been opened, contamination from water condensation or dirt is more likely to occur. Both dirt and water condensation can reduce the oil’s effectiveness as a lubricant in the engine.
Oxidation can be another possible cause of degradation in a motor oil container that has been opened. When molecules in the air react with the molecules in the oil, it can increase the viscosity which forms sludge or sediment.
Oxidized oil can also be more acidic, which may rust and cause corrosion to any metal surface it comes into contact with.
In general, it’s better to keep any motor oil you may purchase sealed until it’s ready to use.
Check the seal on any bottles you buy from the dealer to ensure it hasn’t been opened, and always check opened bottles for any sign of contamination or degradation.
How To Check If Your Motor Oil Is Expired
It can be hard to tell whether you have expired motor oil before pouring it into your engine, but there are several steps you can take.
Check the Expiry Date
First, look to see if there is an expiration date on the bottle. Obviously enough, if it has passed its expiration date, just throw it away. Most motor oils have no specific expiry date but will have a recommendation stating how long you can store them for.
Again, if you know the bottle of oil is more than five years old, dispose of it rather than risk the damage it can cause to your vehicle and its different components.
All oil bottles have a series of numbers, usually found on the base. The laser-printed date indicates when the product was made, not the expiry date.
Do a Color Test
If you’re unsure of the expiry date or purchase date, one way to spot expired oil is to check the color of the oil.
If it has a pale brown color and looks clear, it’s generally good to go. If your unused motor oil is significantly darker or black, this can indicate oxidation, while a haziness or milkiness can be from contamination of water or dirt.
The consistency of the oil can be another good indicator that you should keep an eye on—oils that are solid, thick, or very sticky are less effective than a thin oil which pours easily.
If you notice any separation in the oil or deposits on the bottom of the container, you should replace it and not use it. Just shaking the container will not redissolve the deposits in the oil.
How Does Conventional Oil or Synthetic Motor Oil Expire in the Engine of Your Car?
When the oil is used in your car engine, it’s more prone to all sorts of factors that can affect it while it’s still stored in a container.
The mechanical action of the car’s engine will lead to higher temperatures, which can lead to the motor oil thickening over time. The oil will also be more prone to contamination from soot or microscopic slivers of metal as it circulates around.
Other engine issues like a faulty cooling system or water pump can lead to water getting into the oil, affecting its viscosity.
With a blown head gasket, your oil will take on a milky, almost cappuccino texture and should be replaced as soon as the gasket is resealed.
Oftentimes, environmental factors like icy cold weather can also cause motor oil to form a sludge, which may eventually prevent it from flowing around the engine.
Some synthetic oils will have synthetic additives which can prevent oxidation or reactions to temperatures, and can last longer before changing.
Most mechanics will recommend changing the oil in your car every few thousand miles, but some synthetic motor oils will be sold as 5,000- or even 10,000-mile oils.
To be sure about this, check with your mechanic how often you should change oil at your next scheduled vehicle maintenance, and ensure you use the most suitable oil for your car and driving conditions.
Synthetic Motor Oil and Conventional Engine Oils: Is There a Difference?
Synthetic oils last longer in your car engine and will need changing less frequently for a number of reasons:
- Being man-made, there are no impurities like in conventional oils. This makes synthetic oil last longer.
- Synthetic oils are designed to be friendly to your engine components, using oil additives that prevent corrosion, and can work better in both extreme heat and cold temperatures.
- Additives in synthetic motor oils contain ingredients that prevent breakdown and separation from occurring.
- There’s less build-up of sludge in synthetic oil, and they reduce the build-up of ash.
Synthetic oil can still expire when not used for extended periods of time, though, and will need to be correctly stored – as with traditional oils.
Most of the benefits will actually be for the car when used in the engine. Some additives in synthetic oils will make storing them easier, especially the temperature-fighting components.
Conclusions and Recommendations
To sum up, most types of engine oil (conventional or synthetic oil) have no specific expiration date, rather recommendations for how long you can store it.
These guidelines also include rules about where you need to store it, at what temperature, and how often you should change it in your engine.
Oil that hasn’t been used for a long period of time may have turned quite thick, which is not good for the engine, especially if it has been stored at the wrong temperature.
If the container is opened, ensure you store the oil in a cool, dark place away from moisture and dust.
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