Synthetic oil outperforms conventional oil in terms of quality and performance. We all know that conventional oil degrades over time, and synthetic oil is no exception. However, synthetic oil lasts longer than conventional oil.

Typically, synthetic oil has a 7-8 year shelf life. Following that, it is not advised to use that oil because it will not properly lubricate the engine. This article will go over how long engine oil takes to degrade while sitting in a car or when it is sealed. We’ll also look at how to determine whether or not the engine oil is degraded.

How long can synthetic oil sit in an engine?

Many factors influence how long the engine oil will degrade. If the engine oil has been used previously, it will degrade quickly when seated in the engine. Environmental factors are also important. We’ve seen similar cases with the expiry of oil filters.

In cold weather, engine oil traps more moisture. This allows bubbles and foam to form in the engine oil, making it unusable. If synthetic oil is left in the car for an extended period, it loses its lubrication power. This is because external moisture, dirt, and debris can cause the oil’s viscosity to decrease.

If the oil is left in the car, it can last 6 to 12 months. Synthetic oil contains additives that help them last longer when sitting in the engine. Anti-foam additives such as silicon prevent the formation of bubbles and foam in engine oil.

How long does synthetic oil last unused?

Conventional oil can easily last for 5 years if left unused. Because synthetic oil contains better additives than conventional oil, it can easily last 7-8 years if stored properly.

How can you tell if synthetic oil in the engine is bad?

1. Unused oil

If the engine oil has been unused and sealed, the best way to determine whether the synthetic oil is still usable is to look at the expiry date. The expiration date is printed on the bottle. Some brands only show the manufacturing date; in that case, add 7 to 8 years past the manufacturing date and consider it the expiry date.

2. Oil sitting in the engine

If the oil has been sitting in the car for an extended period, you should check to see if it is still usable. Start the engine to confirm this quickly. If the engine oil is no longer usable and needs to be changed, you may notice the following symptoms when starting the engine:

  1. Oil light will turn on
  2. Cranking sound from the engine 
  3. Engine struggles to start

It is critical to thoroughly inspect the engine before operating the vehicle, as this can result in permanent wear and tear.

How to Check If Oil is Degraded

  1. Apply some oil to your fingers with a dipstick.
  2. Examine the color of the oil; if it is dark brown or black, it has most likely degraded. If the oil is milky, that’s a separate issue.
  3. Rub engine oil between your fingers to test the thickness. If it has a thick consistency, it is most likely clogged and no longer useful.
  4. Smell the engine oil; it is likely degraded and useless if it smells like burnt oil.

How to avoid synthetic oil from degrading quickly?

If you have extra synthetic engine oil that is not being used in the engine, you should store it properly so that it goes smoothly before its expiration date. 

  1. Ensure that the oil bottle is properly sealed to prevent engine oil from being exposed to air and moisture.
  2. Despite additives, high temperatures can affect oil viscosity. Avoid exposing the engine oil to extreme heat or cold. (A temperature range of 40 to 80 degrees is recommended).
  3. Light can cause engine oil to degrade over time. To store the oil, use dark-colored packaging or wrap the oil bottle in a dark-colored sheet.
  4. Avoid opening the seal even once if you do not use the oil. Once opened, engine oil bottles should be used within one year because air and moisture can cause them to degrade.

FAQs on Does Synthetic Oil Degrade Over Time

Synthetic oil lubricates your engine properly, but it has some drawbacks. If you use a premium brand of fully synthetic oil, it can be a little expensive. In addition, synthetic oil performs poorly in cold temperatures compared to conventional oil or synthetic blend oil.

Use of synthetic oil shouldn't go beyond 15,000 miles. Even if the synthetic oil has been sitting in a car, using it is not advised after 6-12 months.


To summarize, synthetic oil is a high-quality engine oil that can last for many miles. It, like other oils, degrades over time if left unused. Unopened synthetic oil bottles typically have a shelf life of 7 to 8 years. 

However, in an unused car, synthetic oil can be stored for 6-12 months. It is best to change the engine oil if it has degraded to enhance the efficiency and longevity of your engine.

Similar Posts

Leave a Reply

Your email address will not be published. Required fields are marked *