Why is there a time limit – in addition to a mileage limit – on motor oil?

Most vehicles carry a motor oil service-life recommendation that includes a duration of time in addition to a mileage distance. For example, your vehicle might call for an oil change every 5,000 miles or six months. It’s obvious that thousands of miles of driving will take its toll on engine oil, but less obvious is the role time plays in breaking down motor oil.

Even when you’re not driving, chemical changes take place within motor oil that lead to degradation and the need for an oil change. Oxidation is a prime culprit. The interaction between oxygen molecules and motor oil molecules naturally leads to chemical breakdown. Just as oxygen causes a cut apple to brown or exposed metal to rust, it breaks down base oils and reduces motor oil’s effectiveness. Although synthetic base-oil molecules are naturally much more resistant to oxidation than conventional base-oil molecules, they eventually succumb to oxidation’s attack. Oxidation can lead to increased oil viscosity, which negatively affects energy efficiency. It also causes the formation of harmful deposits and sludge.

Your vehicles are also subjected to temperature swings, even when not in use. Temperature swings cause condensation to form inside the engine, leading to water contamination. Not driving for extended periods – or taking short trips that don’t allow the engine to fully warm up – allows water to remain in the oil rather than evaporating and exiting through the tailpipe. Water contributes to engine corrosion.

When you do drive, contaminants form as natural byproducts of combustion. Acids lead to sludge formation and corrosion, and those acids and other contaminants continue to affect chemical changes in the oil, even while not driving.

Even though all motor oils have to eventually be changed regardless of mileage, high-quality synthetic oils – like AMSOIL synthetic motor oils – allow you to go longer between oil changes for maximum convenience and cost savings. Premium synthetic motor oils also offer increased resistance to oxidation for excellent engine protection, making them the right choice even if you don’t practice extended drain intervals. AMSOIL synthetic motor oils are formulated with advanced chemicals that resist breakdown, disperse contaminants and clean internal parts to continue delivering outstanding performance and protection long after conventional oils have to be changed. Check out all AMSOIL synthetic motor oils for passenger cars/light trucks.

Signature Series Synthetic Motor Oil
XL Synthetic Motor Oil
OE Synthetic Motor Oil
European Car Synthetic Motor Oil

Photo credits: (c) Can Stock Photo