How true are the performance claims of synthetic engine oils?

Choosing an appropriate engine oil for your vehicle can be utterly confusing. A vast selection of oil brands exist, each with specific performance properties. Synthetic engine oils are routinely touted as superior to conventional oils, with stated benefits such as high-temperature stability, high film strength and a naturally high viscosity index.

Lubricant manufacturers and automakers claim these attributes are advantageous in modern engines operating at higher RPMs and temperatures. They advise synthetic lubricants will keep your engine cleaner, minimise engine wear, improve oil flow in low temperatures and deliver better protection at high temperatures. The theory goes that conventional oils break down faster under extreme engine conditions presented by leading-edge engines.

Conventional motor oils are refined petroleum products, derived directly from crude oil through a process of hydrocracking or solvent refining. API (American Petroleum Institute) Group II is the most common base stock used in the production of quality conventional oils. Similarly, synthetics start out as crude oils but undergo a more advanced refining and distillation process. The procedure removes impurities, and includes a mix of high-performance additives and fluids, allowing oils to be tailored to the demands of the latest engines. Semi-synthetic engine oil products are also available, manufacturers pronouncing they have similar benefits to “full” synthetic, but at a lower price.

Lubricant manufacturers commonly promote synthetic oils as an upgrade from conventional oils, and price them accordingly. A recent survey of 3,423 American Automobile Association (AAA) Approved Auto Repair (AAR) providers across the United States considered the typical cost of a conventional versus full synthetic oil change, highlighting a USD32 price differential. An average synthetic oil change will set you back USD70, compared to USD38 for conventional lubricants. Even do-it-yourself types require an additional USD17 investment for five quarts of synthetic oil, according to the AAA survey.

We pay more for synthetic oil, and marketing departments place growing emphasis on transitioning to these lubricants. So, are the performance claims of synthetic engine oils genuine, or is this simply marketing “spin”? To determine the validity of assertions surrounding synthetic oils, AAA recently conducted independent research into the differences between conventional and fully synthetic oils. The investigation included an analysis of several performance characteristics, as well as manufacturer recommendations and consumer trends. The results of the research were released in May 2017.

AAA is a federation of affiliated automobile clubs with more than 56 million members in the U.S. and Canada. The independent, not-for-profit association, provides a variety of member services and acts as an advocate for motorists, safer roads and vehicles, better educated drivers and the rights of travellers. Thus, its findings would carry more weight than any lubricant manufacturer’s claim.

The research compared five engine oil brands, commonly available in the United States, using eight ASTM tests to evaluate the performance characteristics of each engine oil. The selected tests evaluated shear stability, deposit formation, volatility, cold temperature pumpability, oxidation resistance and oxidation-induced rheological changes. To be considered for the study, licensing to the latest engine oil specifications API SN and ILSAC GF-5 was mandatory, and individual brands were required to produce the range of conventional and fully synthetic engine oil products.

To ensure the independence of the study and the integrity of the results, AAA engaged two independent ISO (International Standards Organization) 17025 certified testing laboratories to administer the tests, each with considerable experience in ASTM testing for engine manufacturers and oil companies.

The headline research outcomes reinforce claims of improved engine performance for synthetic oils. After combining and averaging percentage differences from each test, AAA found that “synthetic engine oils performed an average of 47% better than conventional oils,” said John Nielsen, AAA’s managing director of Automotive Engineering and Repair.

“With its superior resistance to deterioration, AAA’s findings indicate that synthetic oil is particularly beneficial to newer vehicles with turbo-charged engines,” he said.

All vehicles can benefit from using synthetic engine oils suggests AAA, and following the results of the research AAA Sponsor publicly urged drivers to consider switching to synthetic oils. Interestingly, this push to synthetics is not as pronounced from vehicle manufacturers, with only a limited number of OEMs specifically requiring the use of synthetic oils.

As part of the study, AAA analysed fluid requirements for 2016 model year vehicles, discovering only two low-volume, high-performance vehicles mandated the use of synthetic oils. Most vehicle manufacturers simply require engine oils approved to the latest API and ILSAC specifications, alongside “proprietary internal specifications” for warranty purposes.

The AAA investigation seemingly dispels misguided consumer opinion around synthetic oils. Results confirm meaningful performance benefits and engine protection in extreme operating environments, with aging, and potential to minimize engine wear throughout a vehicle’s life. The scale of performance benefits may be questionable; a similar study would benefit from a broader range of engine oil products and larger sampling, to reduce the impact of product outliers on research outcomes.

However, it appears that consumers remain skeptical. A telephone survey of 1,007 U.S. adults indicated 44% of drivers are either uncertain, or do not believe synthetic oils are better for their engine.

“It’s understandable that drivers may be skeptical of any service that is nearly twice the cost of the alternative,” said Nielsen.

The price of synthetic oil is certainly preventing greater uptake; 43% of the drivers surveyed use conventional oil because they say synthetic motor oil is too expensive.

However, Nielsen said the “extra USD30 per oil change could actually save money in the long run by protecting critical engine components over time.”