Decades of Declining Viscosity
“How low can you go?” holiday revelers shout at the limbo dancer. Formulators ask the same of original equipment manufacturers wanting to lower engine oil viscosities, squeeze every last drop of fuel efficiency and reduce carbon dioxide emissions by the gram.
Engine oil viscosities have been getting ever lower over the past few years. The SAE’s J300 standard, which defines the viscometric properties of engine oils, was last revised in 2015, when it established two new high-temperature viscosity grades, known as SAE 8 and SAE 12. This was done to formalize viscosities that enabled a definition of grades to achieve even higher fuel economy, which has become one of the major drivers for performance in new engine oils.
As always, parameters have been set for both kinematic viscosity at 100 degrees Celsius and for high-temperature, high-shear, which take the former down to minima of 4 meters squared per second and 5 m2/s.
HTHS, which is a measure of the lubricant viscosity in an engine’s bearings, are down to greater than 1.7 and 2 millipascal seconds, respectively, to support even greater fuel economy. This now allows the blender the ability to formulate SAE 0-W8 and 0W-12 engine oils.
So far, there are only a few of these grades on the market, and they are mainly promoted for hybrids, as OEMs have not yet accepted these viscosities.
This process of formulating “thinner” higher-performance oils has taken more than a century. Things have come a long way since the first engine oils were used in the early internal combustion engine cars of the 19th Century.
One wonders exactly what oil was used in the landmark long-distance journey that established the motor car as a viable form of transport in 1888, when Bertha Benz took her two sons the 106 kilometers (66 miles) from the birthplace of the Benz Patent Motor Car Model III in Mannheim to her own birthplace of Pforzheim.
The oil was probably a mixture of refined mineral oil, which had just started to be available, and a stable fatty oil drip-fed into the engine from a copper reservoir. At 10 liters per 100 km (28 miles per gallon), the fuel economy for this journey was already at an acceptable level, even by today’s standards. But it is unlikely that the oil’s viscosity played much of a part in this.
This pioneering trip garnered an enormous amount of publicity and was a key event in the technical development of the automobile, as well as for the Benz motor company in particular.
The next 40 years, until the early 1930s, was a time of refining progress, when fluids made from mineral oil with a wide range of qualities were used for engine oils. During this period, oil drain intervals shot up from once a week to more than 1,600 km (1,000 miles) due to the improvements made in base oil quality and the introduction of the first additives to combat oxidation and corrosion. It is believed that in the mid-1930s, British lubricant company Castrol produced the first oil in the world to contain these agents, more than 10 years before they became generally popular.
In parallel, another well-known British firm, Duckhams, was also developing improved oils. They became the specified oils for more than 60 British car manufacturers. Eventually, one premium grade called NOL 40 was selected by one of the major manufactures, Morris Motors, which at one time had a market share of 40 percent. Morris would even put a can of this oil under the bonnet (or hood, for our American readers) of new cars. This was a straight run SAE 40, as many engine oils were at the time. Until the mid-1940s, the only classification for these types of lubricants was based on viscosity alone.
The SAE’s J300 standard, which had been established in 1911, more than a century before its latest revision, was used to classify these monogrades, with the grade numbers defined by the average flow rate in seconds in a viscometer. This was for the new motorists to more easily understand the suitability of an oil for their engines. Times have certainly changed.
Quality was mainly judged on field performance, until initially U.S. Military specifications and then the API’s also became widely used in the mid-1940s with SAE finally recognizing the need to define cold-weather grades – designated W for winter – in 1952.
The lubricant specifications for gasoline and diesel-powered vehicles, as defined by the API and then European OEMs and the Committee of Common Market Automobile Constructors, or CCMC in French, included a wide range of engine tests. These evaluated oil’s performance, especially resistance to oxidation, wear and sludge production. Thus began the need for good quality base fluids with the right viscosity and appropriate additives to be able to pass these performance tests.
Suffice it to say that in the intervening 60 years, there have been enormous changes since Alexander Duckham launched the first multigrade engine oil, Duckhams Q 20W-50, which is still available today, until the point where 0W-XX oils could take 35 percent of the global market in the next 10 years.
The challenge for formulators of these new oils now is to meet fuel economy and emission targets set by legislators and demanded by OEMS, while not sacrificing engine protection, reliability and extended drain periods.
What does this mean for the future of the base oils needed to address these viscosities and all those that are still popular in the market? And will there be the resources and willingness to meet these specifications with the emphasis being shifted to electric vehicles?
Mike Peters has more than 45 years’ experience in the oil and petroleum additives industries, having had technical, marketing and sales management roles at Afton Chemical and SIP since 2001. He is currently SIP’s technical support and development manager. He can be contacted for comments at info@LubesnGreases.com