Of all the protective fluids in your vehicle, the most vital one is oil.

It’s so essential that if your engine is deprived of it for even just a minute, it could be irreparably damaged.

Oil lubricates the engine’s moving parts, dissipates heat, and suspends dirt. Understanding its importance, and what’s on the label, can help you keep your car running smoothly.

A bottle of oil is a complicated mixture. About 80 per cent is base oil, with the remainder made up of additives such as detergents, dispersants, antioxidants, and anti-wear agents.

“Synthetic” oils can be even confusing. While they sound like they’re made entirely in a lab, most are still created from a petroleum crude base. These base stocks have undergone a synthesis process to produce consistently-shaped molecules, which makes the oil flow better and provide optimum lubrication. It’s more expensive, but you’ll get longer intervals between oil changes.

On the oil bottle, you’ll see numbers such as 10W-40. This is the oil’s viscosity—how thick or thin it becomes with cold or hot temperatures. Cold, thick oil can’t move easily through the engine when it’s started, while in summer, oil that gets too thin won’t provide enough protection.

Almost all engine oils are multi-viscosity, a blend of thicker and thinner oils to provide a wider range of protection. The first number—the 10W in 10W-40—indicates its cold-weather ability (the “W” means “winter,” not “weight” as some think). The second number, 40 in this case, marks the hot-weather ability.

The lower the first number, the better the oil will handle cold weather, while the higher the second number, the more appropriate it is for hot weather. So a 10W-40 blend, with a higher hot-weather number, is better for summer use, while a 5W-30 blend, with its lower cold-weather number, works best for winter. These are the most common blends you’ll see in Canada, although oil can be graded as low as 0W for extreme cold, or 60 for very hot climates.

Of all of your car’s fluids, oil also needs to be changed the most frequently, although when to do it isn’t always cut-and-dried. With synthetic oils now so prominent, including in new cars delivered from the factory, oil change intervals are typically much longer than they were in the past.

Some believe that the manufacturers’ scheduled maintenances are unnecessarily close together, but an oil change is relatively cheap insurance. You won’t hurt your engine by changing the oil too often, but leaving it too long can lead to premature engine wear.

Also, it’s important to understand “severe” engine use, where your oil should be changed more frequently. Severe use includes using the car primarily for short trips, especially in cold weather, when the engine doesn’t get to optimum operating temperature; towing a trailer; or driving frequently on dusty roads.

You also need the right amount of oil. Check the level after the car’s been sitting for a few minutes, so the oil can drain to the bottom for an accurate measurement. Pull out the oil dipstick, wipe it off, insert it again, and then pull it out and check the level against the markings on the stick. If it’s low, add some and then check the level again. Don’t overfill: the oil will foam and won’t protect the engine properly.

If the oil warning light comes on while you’re driving, pull over as soon as possible and turn the engine off to avoid damage. The system checks the oil pressure, not the level (some premium vehicles can do both, but will have two separate warnings). All your oil may have leaked out, or the oil pump—which circulates it into the moving parts—has malfunctioned, so there’s no oil pressure.

There’s a third possibility that the sensor is giving you a false reading, but it’s always best to assume your engine is oil-starved, which means not starting it until you’ve added oil or replaced the pump. With something as vital as oil, playing it safe could end up saving you a bundle.