What oil does my car need?

Wondering where to begin choosing oil for your vehicle? From viscosity grades to semi-synthetics, here’s what you need to know about types, specifications and grades of motor oil.

Wondering where to begin choosing oil for your vehicle? From viscosity grades to semi-synthetics, here’s what you need to know about types, specifications and grades of motor oil.

Daniel Hutson
From the Motor team
minute read
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Posted 24 DECEMBER 2020

Why is motor oil important?

Motor oil is essential for vehicles with combustion engines. It helps keep your engine’s moving parts lubricated and working smoothly, and also plays a role in cooling it to the right temperature. Modern engine oils also contain ingredients that help clean and reduce corrosion inside your car.

Because it’s so important, it’s worth keeping an eye on your oil levels and topping up whenever they get low. Whatever the age of your car, the UK government recommends checking your vehicle’s oil as often as the manufacturer’s handbook tells you to.

Find out how to check and top up engine oil.

Can I use any motor oil in my car?

Wondering if you can use up that old bottle of motor oil you bought for a previous vehicle? The answer is ‘probably not’. Different makes, models and engines need different kinds of oil, so if you have a new car, the chances are you’ll need to buy a new bottle.

You can find out what kind of oil you need by checking your vehicle’s handbook.

What do the ‘W’ and numbers mean?

It’s all about viscosity – how runny or thick the oil is. On bottles of motor oil, you’ll see one or two numbers with or without a W: like 5W40 or 30W. This is the oil’s viscosity grade.

Oils with two numbers in their codes, like 10W50 or 0W40, are called multigrade oils because they include additives that make the oil more or less viscous at different temperatures. The first, lower number tells you the viscosity of the oil in cold temperatures – the ‘W’ stands for winter. The number after the ‘W’ tells you the viscosity at higher temperatures – in other words, when the engine is running.

Although the word ‘grade’ sounds like a measurement of quality, there’s no single best grade of motor oil. The best choice for your engine depends on its age, type and design.

Why does oil viscosity matter?

Viscosity is important because if the oil is too thick, it won’t flow through your engine properly and get to all the parts that need lubrication. If it’s too thin, it won’t give the engine’s moving parts enough protection from friction.

What is oil specification?

Oil specifications are set by bodies like the ACEA (European Automobile Manufacturers Association) or the API (American Petroleum Institute). The specifications on the bottle show that the oil formulation is up to date and has passed the relevant tests.

Different bodies have their own classification systems. For example, the API uses codes starting with the letter ‘S’ for petrol and ‘C’ for diesel, while the ACEA uses codes beginning with ‘A’ for petrol, ‘B’ for diesel and ‘C’ for vehicles that have a catalytic converter or low SAPS emission – that’s sulphate, ash, phosphorus and sulphur.

Some vehicle manufacturers set their own specifications too.

To find out which specification your vehicle needs, check your handbook.

What are synthetic and non-synthetic oils?

Engine oils can be mineral, synthetic or semi-synthetic.

  • Mineral, or conventional engine oils, are made from crude oil that’s been refined and processed for use in your car.
  • Synthetic oils are a more advanced version of conventional oils, made to last longer and be more resistant to high and low temperatures. The catch is that they also tend to be more expensive.
  • Semi-synthetic oils offer some of the benefits of synthetic oils and they’re a bit easier on your wallet.

Some modern vehicles can only use synthetic oils, while older vehicles may be fine with conventional oil. Always follow the advice in your vehicle’s handbook when it comes to oil type, grade and specification.

What happens if I use the wrong oil?

If you’ve put the wrong kind of oil into your vehicle during a top-up or oil change, it’s best to correct the problem as soon as possible.

Unlike misfuelling, putting the wrong kind of oil in your car may not cause immediate serious damage. But running your engine over time with the wrong kind of oil is likely to lead to extra wear and tear inside your car - and could affect fuel economy too.

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