Which Engine Oil Does My Car Need?

Written by Petro Olekhnovych, mobile mechanic in Aylesham, Kent

If you are wondering which engine oil for my car is right, the answer is in your handbook. It lists the grade (such as 5W-30) and the specification your engine needs, and you should match both. The AA says using the wrong oil continuously can cause lasting damage, so the right grade alone is not enough.

Start with the handbook

Your car’s handbook lists the grades and specifications of oil that suit your engine. Look in the section on maintenance or technical data. If you no longer have the handbook, the AA suggests asking the parts department at a main dealer for your make.

The handbook will usually give you two things:

1. A grade, such as 5W-30 or 0W-20. This is about how thick the oil is.
2. A specification, such as an ACEA code or the manufacturer’s own approval. This is about what the oil is made to do.

You need both to match. A bottle with the right grade but the wrong specification is still the wrong oil for your car.

What the numbers on the bottle mean

Engine oils are graded by viscosity, which simply means how thick or thin the oil is. Take 5W-30 as an example:

• 5W is the cold rating. The W stands for winter. A lower number means the oil flows more easily when the engine is cold.
• 30 is the rating at normal engine temperature.

Oil with numbers either side of the W is called multigrade, and the RAC says most cars in the UK use multigrade oil. The RAC lists 10W-30, 5W-30 and 0W-20 among the most common grades. The AA notes that 0W-30 is thinner when cold than 5W-30.

Do not swap to a different grade because it sounds “thicker” or “better”. Use the grade your handbook gives.

Why the specification matters most

The specification tells you what standards the oil meets. The AA names several bodies that set these standards, including ACEA in Europe and API in the USA.

Many manufacturers also have their own specifications. The AA says that if your handbook quotes the manufacturer’s own specification, you must look for it on the oil container. Some manufacturers give an ACEA or API equivalent, but this may be for emergency top-ups only.

The AA also points out that many manufacturer oils are now specialised “long life” oils, designed for very long gaps between services.

Diesels with a DPF need low SAPS oil

If you drive a diesel with a diesel particulate filter (DPF), this part matters. The AA says you must use one of the latest “low SAPS” oils, and that using normal oil instead can block the DPF. The AA lists low SAPS ACEA codes such as C1, C2 and C3. Your handbook will say which one your car needs.

Synthetic, semi-synthetic or mineral?

You will see these words on oil bottles. The RAC explains them like this:

• Synthetic oil is designed to perform better than traditional oils, and is often used in high-performance cars and cars with long service intervals.
• Semi-synthetic is a blend of synthetic and mineral oil.
• Mineral oil is made from crude oil and is the most affordable type.

The type on the label is less important than the grade and specification. If an oil meets the specification in your handbook, it is made to suit your engine.

Topping up and mixing oils

Check your oil level regularly. The AA suggests every couple of weeks and before long journeys. If it needs topping up:

• Park on level ground with the engine off, as the RAC advises.
• Use oil of the right grade and specification.
• The RAC says it is best to avoid mixing different types, and to top up with the same oil that is already in the engine.
• Add a little at a time and recheck the dipstick, so you do not overfill.

What if you used the wrong oil in an emergency? The AA says a small amount of the wrong specification is unlikely to cause problems. The risk comes from using the wrong oil continuously, or filling the whole engine with it at an oil change. That can lead to faster engine wear and damage to emission systems such as the DPF.

If your car is using a lot of oil between services, do not just keep topping up. Get it looked at.

What about older and classic cars?

The AA says newer specification oils are usually, but not always, suitable for older cars, while older specification oils should not be used in newer cars. Because of that “not always”, if you have a classic, check the original handbook or ask someone who knows that engine.

For how often the oil should be changed, see our guide on how often you should change engine oil.

How we can help

We do engine oil and oil filter changes, on their own or as part of an interim or full service. We are a mobile mechanic based in Aylesham and we come to your home or workplace, so there is no need to drop the car at a garage. We cover Canterbury, Dover, Deal, Sandwich, Folkestone and the villages in between. See our areas we cover page.

We use the grade and specification your handbook calls for. We also look after classic and vintage cars, including air-cooled VW engines. Labour is £30-£50 per hour depending on the job, parts and oil are extra, and we agree the price on WhatsApp first. Our car service checklist shows what else we look at.

Worried about your warranty? Read whether an independent service affects your warranty.

Frequently asked questions

Can I put 5W-30 in a petrol car?

Yes, if your handbook lists it. The AA says 5W-30 is suitable for both petrol and diesel engines, but your car may also need a specific specification, so check that too.

How much oil does my car take?

The RAC and AA both say most engines take between 4 and 6 litres. Your handbook gives the exact amount for your engine.

Does the oil brand matter?

What matters is that the oil meets the grade and specification in your handbook. Look for those details on the container rather than the brand name.

What happens if I put the wrong oil in?

A small top-up of the wrong oil in an emergency is unlikely to cause problems, according to the AA. Using it long term can lead to engine wear and, on diesels, a blocked DPF. Get it changed back to the right oil at the next chance.

Need help? Send a WhatsApp to 07563 350335 with your car’s make and model and we’ll come to you.

Sources

• AA: Which oil does my car need? Find the right viscosity
• RAC: What engine oil does my car need?