I always buy two 5-quart jugs of Mobil 1 for my 2009 SRT. That leaves 3 quarts leftover in an opened jug. So, I was wondering, how long can oil last? After researching this matter, I discovered that oil companies state that motor oil if unused, unopened and stored in its original container out of extremes of temperature, will last for an “extended period." They then go on to suggest that the oil shouldn’t be used after a few years- the exact period varying between 2 years up to 5 years (Mobil). The manufacturers’ advice on storage gives some clues as to what might happen to degrade the oil. Extremes of temperature can affect oil in different ways. Too hot and thermal breakdown occurs reducing the oil’s viscosity (its “weight” or thickness), which if used leads to a decreased flow rate and in turn to increased oil consumption, the build-up of deposits and potential damage to engine surfaces. Too cold and sludge will form in the oil, blocking engine oil passages and eventually becoming too thick to flow at all. Another possible degradation cause is oxidation, more likely with a container that’s been opened, which is where the oil molecules react with oxygen molecules in the air. This time, viscosity increases forming sludge and sediment. Oxidizing oil can also increase acidity and start to rust or corrode any metal surfaces it contacts. An opened, partly used container also renders the oil more susceptible to contamination from water condensation or dirt, both of which reduce its effectiveness as a lubricant.
I buy my oil the same way. Then on the second oil change, I only have to buy one 5 quart jug. There’s no way I’m throwing away 3 qts of unused motor oil!
