The grade or viscosity of the engine oil is determined by the numbers on the oil bottle like 5W-30, 10W-40, etc. The number before ‘W’ stands for the SAE viscosity of the oil at lower temperatures, whereas the number followed by ‘W’ denotes the viscosity at higher temperatures. The lower the value of the first digit, the thinner the oil is at lower temperatures. So a 0W-20 oil will be thinner than 5W-20 oil at 0℃. These are called multi-grade oils and they can be used throughout the year without switching oil grades. So in theory, you do not need to change the engine oil in your vehicle if you are already running an oil with the right winter viscosity like ‘5W’ or ‘0W’. Since Canada is prone to harsh winter seasons, your vehicle manufacturer may recommend switching to thinner oil for the winter seasons. Refer to your owner’s manual for the right engine oil grade for your vehicle.