Currently reading: What’s the best oil for my car?
Choosing the best oil for your car's engine can be tough, given the large number of options available. Our guide can help you make the right choice
Autocar
News
6 mins read
30 September 2020

Oil is one of those mysterious substances for many car owners.

Unless you’re an enthusiast, you may well open your car’s bonnet only when something goes wrong – you’ve run out of washer fluid or there’s an alarming amount of smoke coming from somewhere. But keeping the car well lubricated is one of the most important maintenance jobs, because unwanted friction in a fast-moving engine usually leads to bad, potentially expensive news.

Advanced mechanical technology in modern cars means that modern oils are more complex than ever, according to David Wright, director general of the United Kingdom Lubricants Association.

He says increased regulations on vehicle emissions and increasing demands from consumers for performance uncompromised by advanced fuel economy have meant that the lubricant industry of oil blenders and marketers has had to keep up with manufacturer demands as they chase better efficiency.

“Smaller oil sumps mean we are all using less oil each year but the oil we are using has to work twice as hard,” Wright says. “Car manufacturers today are demanding thinner and lighter engine oil viscosities to achieve enhanced fuel consumption in a smaller, more powerful engine while at the same time reducing emissions.”

This means that getting the right oil for your car is more important than ever. Get it wrong and while you won’t see instant disaster as you would if you’d put diesel in a petrol car, you will subject your engine to excess component wear.

“You won’t see an issue immediately. It’s not like putting contaminated fuel into your vehicle,” says Wright. “But within 20,000 miles, you could have severe operational issues.”

What kind of oil you need depends on the engine. All new cars will come with a recommended grade listed in the manual and usually a recommended manufacturer, too. The grade will be shown in numbers, separated by the letter ‘w’ – for example, 5w40.

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“Put simply, the viscosity of an oil gives you an indication of its resistance to flow at given temperatures,” Wright explains. “The ‘w’ rating, preceded by a number, gives you an indication of how the oil flows at winter temperatures and the last number indicates flow in summer temperatures.”

However, the viscosity alone isn’t enough to indicate how well an oil will protect your engine. There are numerous tests that car manufacturers go through to formulate engine oils and these are ratified by an organisation called the European Automobile Manufacturers Association, known as the ACEA (an acronym of the organisation’s French title). The ACEA determines the exact requirements needed to meet the demands of different types of modern engine. The specifications, known as ACEA Oil Sequences, are renewed every four years but are backwards compatible for older vehicles. 

“The high costs of investment in engine oil technology run into six or even seven figures for a set of engine tests. Oil blenders, manufacturers and marketers have to be certain that the lubricants they sell are suitable for a given application,” Wright says.

Each ACEA specification is denoted by a letter, followed by a number, which identifies the class of oil and a category within that class – for example, ACEA C3. This specification will be indicated on the oil packaging and the car manufacturer's manual will again specify which you should go for.

But what if you can’t find the exact recommended oil? Wright says drivers should tread carefully, because using the wrong oil can cause damage to your car’s engine.

The problem is that the oil industry is self-certifying. The ACEA defines the specifications, but it’s up to the manufacturers to make sure that the products they put out meet them. A technical organisation called ATIAL spot-checks products of its members every few years, but largely it’s down to the industry to self-police. Some lesser known oil suppliers have been known to label their products as a certain specification but not meet the standards.

“Sometimes it distorts the marketplace if you get some less reputable new entrants into a market selling product below the cost price of other, more reputable blenders. That’s when you get some questions raised.

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“If something looks too good to be true, then it probably is,” Wright says. “If you have been offered the latest specification, fully synthetic engine oil in the pub for £1 a litre, then it probably is too good to be true.”

To combat such products and to check the quality of products, the UKLA launched the Verification of Lubricant Specifications (VLS) service. Anyone can suggest a product for it to test, and if it’s found to be wanting, the UKLA will ask the marketer to quarantine or recall the product, and relabel or reformulate it. Wright says that since the VLS was launched in 2013, it has made a positive impact on the quality of lubricants sold in Britain.

“I think we’re almost there,” he says. “Some of the newer companies are marketing strange formulation that need investigating but, on the whole, the UK market is quite compliant.”

Conversely, some manufacturers produce oils that go beyond the required specifications.

“Some manufacturers will blend to the base line and some will look to exceed it, to develop some form of quality positioning around their brand,” Wright explains. “It’s usually the multinationals, the big companies that will make them even better than the specifications. So if an oil specification says it’ll last for 15,000 miles, they’ll make it so it lasts 20,000 miles, for example. They’ll put a richer mix of additives into the formula to make sure that not only does it not produce wear in an engine, but it’ll help protect the engine over time, too.”

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Quick questions

How does oil vary?

Oil comes in different viscosities, signified by a grade number, such as 5w40. It’s also blended for different types of engines, signified by an ACEA specification, such as ACEA A1/B1.

What oil suits what car?

The type of oil recommended by the car manufacturer will be listed in the manual. It may recommend a particular brand, but the grade and ACEA specification are the important things to look for.

Does brand matter?

As long as the grade and ACEA specification is correct, you should be fine. However, David Wright of the United Kingdom Lubricant Association recommends choosing reputable manufacturers. Some firms will blend more advanced, expensive oils that exceed the specifications on the packaging.

What about cheaper brands?

Again, as long as the grade and ACEA specifications are correct, then everything should be okay. But oils from some newer, less reputable brands on the market have been found not to meet the claimed specifications. The UKLA’s VLS service investigates complaints and tests products to see if they’re compliant and has an archive of its findings on its website - http://www.ukla-vls.org.uk.

What happens if you use the wrong oil?

Using the wrong oil will put undue stress on the mechanical components of your engine. Badly lubricated parts will wear faster and so decrease the life of the engine.

How often should you check your oil?

There’s no set rule. Those who drive more should check more often. David Wright suggests everyone should check their vehicle's oil levels at least once a month.

How often should you change the oil in your car?

This will vary from car to car and will be mentioned in the car’s manual.

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Glossary of terms

ACEA - European Automobile Manufacturers Association. An organisation that represents European vehicle makers and determines the requirements for modern lubricants. Specifications for different types of oil are denoted by an ACEA figure on packaging, such as ACEA A1/B1.

ATIEL – Industry association of European lubricant manufacturers and marketers. The acronym comes from the French “Association Technique de l'Industrie Européenne des Lubrifiants”

Grade – the viscosity of your engine oil, signified by two numbers that indicate oil flow in winter and summer temperatures (eg 5w40). The lower the numbers, the thinner the viscosity.

SAE - Society of Automotive Engineers. The US-based body that defines how oil viscosities are defined and regulated.

UKLA – United Kingdom Lubricants Association. Body representing businesses in the British lubricant industry.

VLS – Verification of Lubricant Specifications. A non-profit service launched by the UKLA to investigate complaints of non-compliance with lubricant specifications.

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Comments
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Peter Cavellini 10 July 2020

Two.

 In three years and and 48,000 odd miles, it's only had two oil changes, and that was when the Garage phoned to inform me(BMW).

drumtochty 8 April 2020

The GTX advert was referring

The GTX advert was referring to a Petrol Engine starting from cold. In those days a diesel engine used a diesel engine lubricant.

Starting from cold there was a lot of petrol used by the choke that tended to wash the cylinder bores of oil and the clearances on the cylinder bores dynamically was not as good as it is now.

There would be more wear and a lot of engines in the late 1960's were well past their peak performance at 75,000 miles even after a cylinder head off decoke at 40,000, due I'm sure to lack of motorways therefore more stop start driving.

Today we have stop start systems which only work when the engine is hot, therefore no cylinder wash from a cold start mixture enrichment or oil draining off the bores overnight. I can see no way that the engine will have any real additional wear.

XXXX if you still have this worry at your next oil change have a used engine oil analysis done cost circa £30 and I assume you have switched off the stop start system. Then have it done at the next oil change with this time the stop start system switched on. Again about £30.

Post both the used oil analysis results to the Bobistheoilguy website and have the guys there advise if there is a significant difference in wear. 

No need to wonder what is the best thing to do to reduce engine wear as you will have the evidence before you. It is the Iron or FE wear metals in the used oils you are wanting to look at. I look forward to you posting the results of your future used oil analysis results.

xxxx 8 April 2020

Oil advert

I believe the rule applies to both types of ICE's, afterall they work in pretty much the same way.

As to worrying about my oil, I don't because the stop-start gets turned off every time I start the car and I don't have a Hybrid.

You forgot to comment on diesel hybrid's going straight from 0-3000rpm under load when stone cold and oil not being in the places it normally is. 

As to oil analysis, this isn't an F1 website so unless you've a problem you're pretty much wasting your money

 

xxxx 8 April 2020

Stop Start and hybrid

I would ask the question what effect does starting a diesel engine from stone cold and it near instantly going to 3000rpm when the hybrid battery runs down on a motorway.

And do the old GTX adverts hold true when they stated most engine wear occurs when starting the engine, another reason to turn this PITA (Stop Start) off.