Five engine oil facts every car owner should know

Engine oil is the lifeblood of a car’s engine. While most drivers know it needs regular changing, there are a few often-overlooked facts that can help guide owners better in choosing the right oil for their car.

These facts cover basic stuff about oil and a few questions you may have had when taking your car for its routine service. Without further ado, let’s start with fact number one.

You may have heard this online or from people at service centers that once you choose between synthetic or mineral oil, you have to stick with it forever. Fortunately, this is not true. Most modern engines can safely use either mineral or synthetic oil as long as the recommended viscosity grade is followed and the oil meets the correct specifications for the engine.

Switching between mineral and synthetic oil will not harm a healthy engine. Synthetic oil generally offers better heat resistance, improved performance in extreme temperatures, and longer service intervals, while mineral oil remains a suitable option for many vehicles when changed at proper intervals. There is also a middle ground in the form of semi-synthetic oils, which combine mineral and synthetic bases to balance performance, protection, and cost.

The most important factor when choosing engine oil is following the vehicle manufacturer’s recommendations, including the correct viscosity rating and required standards, rather than believing that selecting one type of oil permanently limits your future choices.

You cannot determine the remaining life of motor oil based on its appearance alone, as oil can change color for several reasons. For example, oil in diesel engines often darkens quickly even after a fresh oil change because it is designed to keep soot, dirt, and other combustion byproducts suspended within the fluid. Although the oil may appear dark, its performance may still be largely unaffected.

The best approach to oil maintenance is to follow the oil change intervals specified in your vehicle’s owner’s manual and regularly monitor both your oil level and mileage.

Most of us have glanced at a bottle of engine oil and noticed the string of numbers on the label, but not everyone understands what they actually mean. One common misconception among car owners is that the letter “W” refers to the oil’s weight, when in fact it stands for “Winter.”

Engine oil naturally changes viscosity as temperatures rise and fall, and a single viscosity rating only describes how the oil behaves once the engine has reached normal operating temperature. Cold starts are a different matter. On a cold morning, oil flows more slowly, which is why its low-temperature performance is just as important—especially in regions that experience significant drops in temperature. This is where multi-grade engine oils come in, as they are formulated to perform effectively in both cold and hot conditions and are the standard for modern vehicles.

Take 5W-30 oil as an example. The “30” refers to the oil’s viscosity at normal operating temperature, equivalent to an SAE 30 rating. The “5W,” meanwhile, indicates how the oil flows in cold conditions, based on standardized winter testing set by the Society of Automotive Engineers (SAE). Together, these ratings help ensure proper engine protection, whether you’re starting the car cold or driving with the engine fully warmed up. So, to make a long story short, “W” stands for winter and not weight.

Though it may sound surprising, some engine oils include tiny metal compounds as additives. These compounds, often based on titanium, zinc, or molybdenum, are blended into the oil to form a low-friction layer on engine components. This protective layer helps reduce wear and tear and can even contribute to improved fuel efficiency.

Motor oil, like any other consumable product, has a limited shelf life. Even a sealed bottle of oil does not last forever. Over time, the additives in the oil can settle or break down, reducing the oil’s ability to protect your engine. Using old or degraded oil may compromise its performance, leaving your engine more vulnerable to wear and tear.

Engine oil is also different from liquids like medicine or beverages. Shaking or agitating a bottle may make it appear uniform again, but the oil is mixed at a molecular level, and agitation cannot fully restore its original properties. For this reason, it is best to use fresh oil within the manufacturer’s recommended shelf life, typically around five years for unopened bottles, and even sooner once the container has been opened, around one year. Proper storage, away from direct sunlight, heat, and moisture, can help preserve the oil’s protective qualities.