A reader asks: How long is motor oil usable after the bottle has been opened?

Our answer: Once the seal has been cracked on a bottle of motor oil, the remaining oil should be used up within one year. This guideline also applies to transmission oil and gear oil. Opened bottles of both synthetic and conventional motor oils would have a similar lifespan.

Three Reasons Why Motor Oil Should Be Used Within A Year Of Opening

  1. Condensation- After the seal on the bottle has been broken, the interior is more prone to condensation. Once the oil level in the bottle is lowered, there is more open space for condensation to develop.
  2. Oxidation- As the motor oil becomes exposed to oxygen over time, the chemical makeup of the motor oil changes. Simply put, once the oxidation process has started in motor oil, the capabilities of the oil are severely limited and unpredictable. Therefore, that partial bottle of motor oil that has been sitting on shelf for several years should be used in an oil can or sent to recycling.
  3. Additive Fallout- Over time, the ingredients that make up the motor oil formula can start to degrade. This compromises the capabilities and service life of the motor oil. This process would likely take much longer than a year. This can happen in sealed bottles that have been stored for too long as well.

Motor Oil Storage Tips

  • Store motor oil in dry conditions. Don’t leave motor oil bottles out in the yard or in the back of the truck.
  • Do not store the oil in temperatures below it’s cold-pour-point. If the motor oil freezes and “gels”, this will shorten the lifespan of the motor oil.
  • The ideal storage temperature range for motor oil is between 0°C (32°F) and 29°C (85°F).

Shelf Life Of Unopened Motor Oil Bottles

The shelf life of sealed, unopened motor oil, transmission fluid or gear oil is roughly 5 years. Please note the storage tips above to maximize the shelf life of new motor oil.