Engne oil

How to choose and check your oil

Your engine won’t last very long if it runs low on oil – and if you just use cheap oil without bothering to change it very often, your engine’s days are numbered. Your engine has oil inside for two key reasons; to lubricate the moving parts and to help keep everything cool. As the oil moves away from the really hot bits of your engine, it takes away some of the heat, to help reduce the likelihood of overheating.

How do I know which oil is right for my car?

Checking your oil regularly is essential if you’re to avoid disaster striking, but just what do you put into your car’s engine to make sure it keeps running smoothly?

While it would be easy to assume that all oils are the same, the reality is that – like most things in life – there are cheap options and premium alternatives. Predictably, using a cheap oil will provide a minimum of benefits to your car’s engine; using a better alternative will protect it more fully and it won’t degrade as readily – although you’ll still have to renew it just as often.

There are three key types of oil: mineral, synthetic and (in the middle) part-synthetic.

    • Mineral oil is produced from crude oil; it’s the most basic (and cheap) oil there is, and as long as you’ve got an oldish car plus you change the oil regularly, there’s no reason to shy away from mineral oil.
    • Synthetic oil is the best stuff, as it’s created in a lab and full of high-quality ingredients. It’s the most expensive oil around, but as you shouldn’t have to change your engine’s oil more than once a year, it’s not a massive investment using this instead of the cheapest lubricant you can lay your hands on.
    • In the middle is perhaps the best oil for you (if not your car’s engine) in that a part-synthetic lubricant is of a higher quality than the mineral stuff, but it’s not as costly as a fully synthetic alternative.

What do those numbers mean?

Look at a bottle of engine oil and you’ll see that it’ll say something like 20/50 or 10/40; these are the viscosity ratings. An oil’s viscosity is how runny it is, and those numbers refer to its thickness when it’s cold as well as at the engine’s operating temperature.

So when an engine is cold its oil will be relatively thick, so not very runny; heat up the engine (and therefore its oil), and things change radically, with the oil becoming much thinner, so much more runny.


The lower the number, the thinner the oil – and the better it’ll protect your car’s engine. So while a mineral oil might be rated at 20/50, a fully synthetic oil might be 10/30 – which means it’s thinner when it’s cold, as well as when it’s hot.

You can find the right oil for your car’s engine by sticking your car’s registration number into this Halfords web page – and also don’t forget to check out our page on how to check your oil. It might just save your engine from an early death.

How do I check my oil?

Three out of four Brits don’t know how to check the oil in their car, according to research from Mobil 1. More worryingly, almost half of drivers don’t know why oil is used in their car’s engine.

The research also found 94% of motorists were unaware that using the correct oil can significantly prolong the life of their engine, as well as potentially improve fuel economy. All of which means that at a time when British car owners are feeling the pinch like never before, they could be driving blindly towards expensive engine problems in the future.

You wouldn’t survive very long if all the blood was drained from your body. It’s the same for your car’s engine; let it run out of oil and it won’t be long before the whole things destroys itself. That’s why you need to make sure there’s enough oil in the engine. It takes just a couple of minutes; here’s how.

    • Park your car on level ground and switch off the engine.
    • Open the bonnet and leave the car for five minutes, for the oil to settle.
    • Pull on the loop of the dipstick and take it all the way out.
    • With a clean paper towel or rag, wipe the oil off the dipstick.
    • Put the clean dipstick back in the engine, pushing it all the way in.
    • Pull the dipstick back out; towards the bottom end will be two markings. The oil level should be somewhere between these; if there’s no oil showing at all, the engine is dry and it’ll soon be wrecked.
    • If the oil on the dipstick is below the line marked ADD, put in a small amount of oil.
    • Add oil by unscrewing the oil filler cap, on top of the engine.
    • Using the correct type of oil (check the handbook), top up the level.
    • Check the level again and add more if necessary; don’t add too much oil as removing oil is much harder than adding it.
    • Put the oil filler cap back on and make sure it’s tight.
    •  Make sure the dipstick is back in place as well.