Cars need fuel and oil just like we need water and blood. If you don't eat and drink well enough, your body won't last very long. Likewise, your automobile requires quality fluids and regular maintenance to survive and perform as it should.
Basically, engine oil separates and lubricates moving parts, prevents rust and residue buildup, keeps dirt from infiltrating the engine, and cools the latter down by carrying heat away from said moving parts.
That's good to know, but when is the right time to change the oil?
The answer depends on the vehicle you drive, so check your owner's manual for a specific recommendation by the manufacturer. If you got rid of it to make room for ''more important'' stuff in your glove box, chances are you can get a new copy from your local dealer or download the electronic version online.
For example, you must change the oil (and filter) every 4 months or 8,000 kilometres if that's the service interval specified in your owner's manual.
Vehicle age, engine type (naturally-aspirated, turbocharged, supercharged), temperature, distance/duration of your trips and other factors will affect how quickly the oil deteriorates, thickens and completes its life cycle.
Now that you're familiar with the role played by this precious fluid as well as its service schedule, you can determine which type of oil is the best fit.
Engine oil contains about 70 to 85 percent base oils and 15 to 25 percent additives. The latter modify the base oils or add unique properties to prevent corrosion and oxidation, reduce friction or help high-mileage engines run smoother, for example.
Since all vehicles are confronted with temperature variations, especially in climates like ours, they must use multi-grade oil. Single-grade oil is available but not really suited for performance in a wide range of temperature conditions.