Use the viscosity grade and specification in your owner’s manual or service book. Choose an oil that shows both the correct grade, such as 5W30, and the required approval or standard on the label, then compare brands and prices among those.

The first number, followed by W for winter, shows how easily the oil flows when cold; both are rated 5W. The second number shows thickness at normal operating temperature, so 5W40 stays thicker than 5W30 when the engine is hot. Use the grade your vehicle maker specifies.

Follow your vehicle maker’s service schedule, which sets an interval by distance and by time, whichever comes first. Frequent short trips, towing, heavy loads or dusty roads can call for shorter intervals, so check the schedule for these conditions too.

Oils with the same grade and specification can generally be mixed when topping up. For an oil change, it is best to use a single oil that meets your vehicle’s requirements, and never top up with oil that doesn’t meet the specified grade or approval.

Check coolant, brake fluid, power steering fluid where fitted, and windscreen washer fluid, along with your engine oil level. Brake fluid absorbs moisture over time, so replace it at the interval your vehicle maker recommends.