Oil Buyer’s Guide

Car engine oil is derived from the crude oil extracted by oil rigs, but it goes through a few processes to become the final product you put in your car.

The oil has to be refined into something with a lower viscosity – meaning its much thinner and smoother – to help the engine turn over more easily and ensure that the oil can circulate quickly around the engine when you start up. It also contains additives to help clean and reduce wear and tear on internal components.

Engine oil is the lifeblood of your car. In certain sections of your engine, oil creates a layer between the moving parts that helps to prevent friction. Too much friction means the components will wear down faster, causing expensive damage to your car. That’s why it's incredibly important to make sure your car has enough oil. If you do let your car run out of oil, then you run the risk of engine overheating, damage to expensive components, and eventually complete engine destruction.

While the vast majority of engine oil is, of course, crude oil, there are a few things added to make the oil suitable for your car. You'll also find things like detergents, which clean the spaces between moving parts and nooks and crannies where grime and old oil can build up, anti-wear (AW) additives that prevent certain materials from wearing out sooner, dispersants that prevent oil and other waste materials from clumping together, and viscosity improvers that help the oil to flow better, especially when it's cold.

Thanks to the extreme heat and pressures inside car engines, oil degrades over time and becomes less able to protect your engine, so you'd eventually be left with no oil left in your engine at all if you didn't top up regularly. If your car is reaching a ripe old age, then the seals and gaskets may not be as tight as they once were, letting small amounts of oil leak out too.

IMPORTANT: if your car is leaving puddles of oil on your driveway or you have to top up every few weeks, visit a mechanic as soon as possible, as oil leaks can lead to bigger, more expensive problems as time progresses. Pop into a Halfords Autocentre or book an appointment.

When you go to buy motor oil, you'll notice that there's a code on each container. These numbers relate to the oil's viscosity (how well it flows around the engine) in warm and cold conditions, which is an indicator of how it'll perform depending on the outside temperature.

Thanks to the hugely varying temperatures in the UK, the oil we put in our cars is different to the oil you'd use in warmer countries. That’s why we use the dual numbering system (known as 'multi-grade' engine oil), rather than single-grade varieties used in hot or tropical climates.

Our handy car engine oil finder will show you exactly which oil you need using just your car's registration number! We also recommend checking your owner's manual to get the right oil for your car, but you can always ask a Halfords colleague if you're in-store and they'll be happy to help you find the one you need.

This really depends on how many miles you do and in what conditions. If you have a long daily commute, then you should check your oil, and top up if necessary, every few weeks. You can see how much oil your car has in the reservoir (where oil sits when the engine isn't running) by checking the dipstick, or for vehicles without a dipstick, use the on-board vehicle information display - if the oil level is low, then you'll need to top up.

Top tip: If you're booking repairs or a service at a Halfords Autocentre, then we'll top up your oil for you as part of the package, saving you a job!

Get a full breakdown of how to check and top up your oil with our handy guide.

Knowing how much oil to put in your car depends on two factors: Your car's engine oil capacity and how much oil there currently is. Check your owner's manual to get an idea of how much oil your car can hold and top up accordingly. Another way to do this is to check the oil level using your dipstick or for vehicles without a dip stick use the on-board vehicle information display.

If the oil is halfway between the first line and the second line, then you'll need to put about half a litre in. If it's just over the first line, put a full litre in. Please note that these amounts refer to the average family car, and you may need to add less or more oil depending on if the vehicle has a smaller or larger engine oil capacity, or a high-performance engine. If you have any leftover oil, then this can be stored safely in your garage in an upright manner and away from heat sources ⁄ direct sunlight for up to 5 years. Be sure to always check the best before date before topping up too.

Just topping your oil up now and again isn't enough to keep your engine in top shape. An engine oil change involves completely draining the engine of oil and replacing it with brand new oil. You can do this yourself, but it can get very messy, so we'd recommend visiting a Halfords technician. They'll also be able to provide a full engine tune-up and potentially add further fluids that will help to clean degraded oil out of your car engine