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The Ultimate Guide to Synthetic Oils: Understanding, Choosing, and Using the Best for Your Vehicle

Synthetic oils have revolutionised engine lubrication. Unlike traditional mineral oils, synthetics offer enhanced performance and protection for a wide range of vehicles.

What type of engine oil does my car need?

You can discover the type of oil that your car needs in the owner's manual, by using our car oil check tool with your registration number, or by getting in touch with us here at Opie Oils. Whilst those on forums may have the best intentions and a wide range of knowledge, be wary of this advice – trust the advice of the manufacturer or a professional only as they will have access to the correct information from oil blenders and vehicle manufacturers.

Buying car oil isn't a straightforward thing, as modern vehicle engines use extremely fine tolerances and subject oils to a series of very different forces, conditions and stresses. So, it's important to understand exactly what engine oils do in your vehicle to make sure you select the best one.

Understanding the role of engine oils in your vehicle

Engine oil is more than just a lubricant; it plays a multifaceted role in ensuring the smooth operation and longevity of your vehicle's engine. Here's what engine oil does:





Improving Efficiency

Versatility Across Conditions

Have a look at our Functions of Car Engine Oils Explained article if you'd like to know more.

Types of engine oils

Mineral Oil: The Traditional Choice

Derived from crude oil, mineral oil is the most basic and affordable type of engine oil. It's widely used in old vehicles, offering adequate lubrication but requiring more frequent changes and suffering performance dips in extreme operating temperatures. It may not even be possible to buy a mineral engine oil that meets the viscosity and performance requirements stated by your vehicle's manufacturer.

Semi-Synthetic Oil: The Middle Ground

Blending synthetic additives with mineral oil, semi-synthetic oils provide better protection and performance, especially in varying temperatures. They strike a balance between cost and quality, suitable for a wide range of more modern vehicles.

Synthetic Technology Oil: A Step Up

Synthetic technology oils are made from mineral oils that going through a process called "hydrocracking" to improve the quality of the base oil. These are not completely synthetic oils, but the additives are similar to those used in synthetic engine oils and they typically offer high performance, meeting the high specifications of today's vehicle manufacturers. To confuse things, many oils labelled as "synthetic" are actually synthetic technology.

Full Synthetic Oil: Superior Performance

Engineered for peak performance and extreme heat, fully synthetic motor oil offers the best engine protection, fuel efficiency, and extended change intervals. Whilst they are usually more expensive than other types of all, there are bargains to be had; many aren't much more expensive than semi-synthetic oils.

True synthetic lubricants are distinguished by their Polyalphaolefin (PAO) base stock, which is manufactured rather than mined and refined. PAO offers excellent thermal stability, oxidation resistance, and low-temperature properties, making it suitable for use in a wide range of operating conditions. PAO-based oils are often preferred where there are extreme temperature variations and demanding performance requirements are present - ideal for high-performance and modern engines.

Understanding synthetic engine oils

Comparing synthetic and conventional motor oils

The core difference lies in their formulation and performance. Synthetic oils provide better engine protection, especially under extreme conditions.

We've written a separate article on the advantages of synthetic car engine oils if you want to delve deeper.

Weighing long-term savings against upfront costs

Although synthetic oils are more expensive upfront, their long-term benefits offset the initial cost. The potential for extended oil change intervals and enhanced engine protection can lead to savings in maintenance costs, not to mention the potential for improved fuel economy and reduced engine wear.

For more information, take a look at our article on the advantages of synthetic oils.

Oil viscosity and its importance

Viscosity, the measure of an oil's thickness and flow, is crucial for engine health. The right viscosity ensures efficient lubrication across temperature ranges. Refer to your vehicle's manual for the recommended viscosity grade or use our engine oil lookup tool.

Oil changing intervals for synthetic oils

Synthetic oils often allow for longer oil change intervals between changes, but this varies based on the vehicle type, usage conditions, and oil composition. Following manufacturer guidelines is crucial for maintaining engine health. Some manufacturers do suggest an oil change interval of over 10,000-miles or every 24-months, but the costs for an oil and filter change aren't great… we generally recommend an annual / 10,000 mile oil service unless your handbook suggests a more frequent interval.

Synthetic blends and semi-synthetic oils

Semi-synthetic oils, a mix of synthetic and conventional oils, offer a middle ground in terms of performance and cost. Their composition, though, can vary, affecting their protective qualities.

Synthetic oils and engine health

Long-term use of synthetic oils can significantly enhance engine performance and longevity. They are especially beneficial in preventing wear and tear, and keeping engines running smoother for longer.

Environmental impact of synthetic oils

While synthetic oils are petroleum-based, their longer change intervals and efficient performance contribute to reduced environmental impact. Proper disposal and recycling of used oil are essential for environmental stewardship.

Keeping up with technological advances

The synthetic oil industry is continually evolving, with recent advancements focusing on extending oil life, improving fuel efficiency, and reducing environmental impact. Innovations also include developing oils specifically for hybrid and electric vehicles, reflecting the changing automotive landscape.

Selecting the best oil for your vehicle

Consider your vehicle's specifications, driving conditions, and budget. If you're unsure what oil to use for your car, then use our engine oil lookup to help you identify the best option for you. All the oils recommended by us will be suitable for your vehicle.

Myths about Synthetic Oils

Do synthetic motor oils damage seals?

This is really not the case. Any oil seals made after 1975 or thereabouts will be entirely compatible with any type of synthetic engine oil. (The same goes for synthetic gear oils and transmission oil seals.)

Everything associated with lubrication is thoroughly tested. The major oil manufacturers do not make oils that attack seals, and seal manufacturers ensure that their products function correctly with modern lubricants!

Are synthetic oils too thin?

It is true that the best synthetic blends can be low viscosity (0w-20 for example, or even down to 0w-16 for some modern oils for hybrid cars), but they do not have to be. It is also true that the latest engines are designed to run on thin oil, which improves power output and fuel consumption.

Even so, thicker synthetic-based grades (10w-50, 15w-50, 20w-50 etc.) are available for air-cooled motors, older engines, or severe high temperature conditions. These grades can also benefit rebuilt classic engines dating back to the 1940s.

Do synthetic oils mean higher oil usage?

Quite the opposite! Oil consumption in well-maintained modern engines is mainly down to the oil evaporating at high temperatures. Synthetic base oils (especially the PAO and ester types) are very resistant to evaporation loss even in low-viscosity blends, so oil consumption is minimised.

Obviously, engines with worn valve guides, defective seals and worn piston rings will use oil regardless, so there is no point in using expensive synthetics as an 'old banger lube'.

Are synthetic oils compatible with other oils?

Yes, they are. All engine oils intended for normal road use in recent 4-stroke engines are compatible with one another, regardless of the base makeup, including mineral, PAO, ester, hydrocracked synthetic, and semi-synthetic.

There is no need to flush or strip down an engine when changing from one type to another. However, on a "specialist note", be careful with the exceptions of castor oil-based racing oils and plant-based engine oils.

Do synthetic oils produce sludge?

Not at all! All synthetic bases are more resistant to oxidation than mineral oil, and sludge is largely due to oxidation. In any case, all motor oils intended for road use meet the higher ACEA and API specifications. One of the main reasons for introducing the API specs back in the 1950s was to deal with oil sludge problems. All high-spec oils run very clean, especially synthetics.

Can synthetic oils be used with catalytic converters?

Yes, exhaust gas after-treatment systems will perform more efficiently and last longer if synthetic-based engine oil is used. Their lower volatility means that less oil reaches the combustion chambers via crankcase ventilation, so there are fewer harmful ash residues from burnt oil to deactivate the catalyst matrix.

Will using a synthetic oil void my warranty

Using the right oil will never void a warranty – and these days, the right oil is usually a synthetic technology or fully synthetic oil. Provided that an oil meets or exceeds the ACEA / API and viscosity ranges specified in the handbook or the manufacturers own specification if given, the warranty will not be affected. By law, OEMs cannot insist that a particular brand of oil must be used to maintain a warranty.

Will a synthetic oil last forever?

Alas not. The better synthetic blends will certainly last longer, especially in high performance or high annual mileage situations, but 'forever' isn't going to happen, simply because contaminants such as soot, and acid gasses from traces of sulphur in the fuel degrade the oil. Good synthetic oils use a very shear-resistant viscosity improver polymer in the oil formulation to keep the viscosity up to spec.

Are synthetic oils too expensive / too good for my car?

You can't go "too good". If you use a suitable oil of the correct viscosity and specification, you'll benefit from the properties of a good synthetic oil. For older vehicles that use a lot of oil or are almost ready for the scrap yard, you might want to keep your spending down, but using the wrong oil can hasten a vehicle's demise. For cars that are worth maintaining, the right types of synthetic oil are a cost-effective way of retaining 'as new' performance, low fuel consumption, and reducing maintenance costs.

Want to know more, or need advice?

If you have any questions or need any advice, we can help. We have what we think is the largest selection of synthetic oil available in one place, from many different oil manufacturers. We're independent, too, and will recommend what we believe is best for your vehicle.

You can call us Monday – Friday 8.30am to 5.30pm on 01209 202944, email us at or use our online oil recommendation tool.

We have a variety of other oil-themed technical articles that may be of interest.