Does Synthetic Oil Degrade Over Time?

There are affiliate links on this article. If you make a purchase through any of the links, I may earn a small commission at no extra cost to you.

Does synthetic oil degrade over time? Many researchers have proved that virtually everything we use or consume has an expiry date. This implies that everything has a time when it’d start to deteriorate, degrade, spoil, etc. (whichever word you wish to use).

Generally, motor oils are made with additives and other chemicals that help achieve the purpose of the oil. These additives and chemicals are subject to disintegration (after a while).

Thus, synthetic oils will surely degrade gradually due to pressure and other factors. However, it would take a longer time for unused oils to expire and become unsafe for your engine.

Does Synthetic Oil Degrade Over Time?

The simple answer is YES, and here’s the explanation you need to know. Synthetic oils contain fewer impurities than regular or conventional motor oils. For this reason, it is safe to ride up to 15,000 miles (if you use synthetic oil) before thinking of oil change.

But, if you use regular oil, you’ll have to change your oil quite frequently or every 7,500 miles. The more impurities in regular oils make them spoil/degrade faster than synthetics.

However, the explanation above refers to oils that have been introduced into the car. Such oils are now subject to extremely high temperatures and mechanical pressures, which are part of the reasons why they degrade over time.

Now, coming to unused synthetic oils, do they also degrade over time? Again, the answer is YES. According to Total, unused motor oil will turn bad if not used for up to two years. This is because the chemicals and additives will surely disintegrate within this period.

In contrast, Mobil assured that unused motor oils could last up to 5 years before it becomes unsafe to use anymore. So, comparing the reports from these top motor oil brands, one can say that motor engine oils (generally) will surely go bad if left for over 3 years (on average).

Would The Oil In My Parked Car Degrade Overtime?

Some people have multiple cars – with many of them parked in a garage. In this case, it is similar to unused oils (explained above). When a car is not being used, the oil inside will last for up to two (2) years or more before it starts to degrade.

However, if the car is sometimes taken out for a drive, do ensure you change the oil after the manufacturer’s recommended mileage.

How Do You Know That Your Oil Has Gone Bad?

How Do You Know That Your Oil Has Gone Bad

As said earlier, everything has an expiry date – to know if the motor oil you bought some time ago has gone bad, check for the expiry date. The expiry date should be on the label or bottom of the gallon. Also, the hue can tell if the oil is bad or not.

Another way to check for spoilt motor oils is this – pour out the oil into another storage and check the bottom of the gallon if you can see some deposits.

When the additives used in an oil disintegrates, they settle at the bottom. This is recommended if the oil has been left for a while before being thought to be used.

What Will Happen If You Used An Expired Oil?

We won’t advise using expired oils for any car engine (whether new or old). Once the additives degenerate and disintegrate, their potent is lost, and they turn to highly-toxic/acidic chemicals.

Thus, instead of protecting your engine, expired oils may promote oxidation, thereby leading to leaks, wear & tears.

However, some mechanics claim that expired motors oils pose no harm if they have not been contaminated by water or any other liquid.

Recommended Reading:



Synthetic oils get contaminated over time with the deposits from an engine. If you’re riding an old car, you should change the oil earlier than 7,500 miles. This is because older engines produce more containments and deposits than newer engines.

Furthermore, always remember to change the oil filter after a while. Using the same filter after several oil changes is not advisable as such action can lead to a critical engine breakdown.

So, does synthetic oil degrade over time? Yes, they do (whether used or not used). The additives in the oil have a maximum shelf life of 5 years. When you purchase a motor oil, ensure to check the production date, as well as the expiry date.

Scroll to Top