How Long Does A Bottle Of Lawn Mower Engine Oil Last Once Opened?

Proper maintenance is crucial for the health and longevity of your lawn mower. It's not enough to simply fill it with gas and pull the cord. You should regularly replace the filters and sharpen the blades for a cleaner cut and a more efficient engine. And don't forget about the oil. Changing the lawn mower's oil is one of the most overlooked mower maintenance tasks that everyone forgets, but one you should prioritize. Aim to change your lawn mower's engine oil at least once per season, or every 50 hours of use, whichever comes first. If you are diligent in this routine maintenance task, you may find yourself with an open, half full bottle of oil. But should you keep it and use it? Or should you pitch it?

It turns out that lawn mower engine oil does have an expiration date after being opened. Manufacturers generally recommend using it within six to 12 months, provided it has been properly stored. If you use the opened bottle of oil after its "best by" date, you could end up damaging your mower. The lubricating properties and protective additives in the oil break down, or settle, after this period of time, which could lead to engine wear or even engine failure.

No one wants to see thick or sludgy oil coming out of the can as you're pouring it into your mower. While it is important to pick the right oil for your lawn mower, it is also key to make sure the product is safe to use and effective. To get the most from your engine oil, store the opened bottle in its original container. Be sure to seal it tightly, no wobbly or barely-on caps. Air accelerates the oxidation process once a bottle of motor oil has been opened, which can introduce moisture to the product. This can cause the oil to become thick, sticky, and unable to lubricate and protect your engine components properly. 

You will also want to store the open oil bottle in a cool, dry place. This means skipping the shed and store in your garage (if it's temperature-stable), or a dedicated basement space. The ideal temperature range for storing most oils is 40 to 85 degrees Fahrenheit to avoid additive separation and viscosity changes. Before you put the bottle away, wipe off the rim and threads to remove any residual oil, ensuring an airtight seal. It's also a good idea to write the opened date on the bottle. If you happen to find a can that is past its prime, be sure to dispose of motor oil the right way.