Currently, there are in excess of 12.6 million trucks in service on U.S. roads. Sales of new Class 8 trucks were just shy of 250,000 units in 2016, and sales of medium duty Class 5-7 units (which include buses, RVs and vocational vehicles) were 229,000. Looking ahead, 2017 sales are projected to be about 500,000 Class 6-8 tractors, almost 100 percent of them diesel powered.

Market research firm Kline & Co. forecasts that between 2015 and 2025 the use of Group I base stocks in heavy duty engine oils will drop by over half, to just 10 percent of formulations. Meanwhile, the share of Group II and II+ will more than double to around 70 percent from their current level of about 30 percent. Group III will increase from 4 percent to 6 percent, and Group IV (polyalphaolefin) barely registers.

On a global basis, Kline projected that change will come slowly to the mix of heavy duty engine oils. As a general rule, monogrades are declining, 15Ws holding their own, and 10W and 5W growing in step with new vehicle introductions. Regionally, though, the changes in viscosity grades are more complex.

North America continues to rely on SAE 15W-40 (about 80 percent of the market), although 10W-XX and 5W-XX are rising. Monogrades are not a factor here, although so-called universal oils for mixed fleets still claim a persistent share of the North American market.

Europe is similar to North America although the viscosity spread is a bit bigger (more SAE 5W-XX and 10W-XX). Monogrades remain relatively constant at about 15 percent share.

Asia-Pacific and Latin America are SAE 15W-40 strongholds (half the markets), with monogrades in the range of 20 percent to 30 percent. That leaves just 10 percent or less for SAE 10W and other light grades.

That is, heavier grades are dominant in most corners of the world, but North America and Europe are leading the way to lighter grades. And in North America this may be snowballing at a faster rate than anticipated. In a presentation last May to the Society of Tribologists and Lubrication Engineers, Chevron Lubricants Shawn Whitacre projected that SAE 10W-30 diesel engine oil would increase in volume in North America over the next several years and reach parity with 15W-40 around 2025.

Whitacre noted that the majority of on-highway fleets will be using API CK-4 SAE 10W-30 by 2022. APIs fuel-saving grade, FA-4 SAE 10W-30, will be coming into use a bit later. Owner-operators and drivers of light duty diesel pickups will be slower to adopt the lower viscosity, he observed.

Theres no question that the key parameter to improved fuel economy in heavy duty engines is high temperature, high shear rate viscosity (HTHSV). Historically, 3.5 cP has been the minimum specification for this important property. Using SAE 15W-40 and the new CK-4 category as a baseline, simply reducing the viscosity grade to SAE 10W-30 will deliver a 1 percent to 4 percent improvement in fuel economy-without lowering the HTHSV limit. Further improvements (2 to 5 percent) can be made by lowering the viscosity of the oil to an SAE 5W-30. The use of FA-4 engine oils with a HTHSV of 2.9 to 3.2 cP will add additional fuel economy benefits.

In a field test run by Lubrizol and Daimler Trucks North America, a fleet of DD-13 powered trucks using CK-4 oils showed 0.5 percent to 1.5 percent better fuel economy when run on SAE 10W-30 versus SAE 15W-40. As reported in a webinar by Fleetowner magazine, a further 0.4 to 0.7 percent improvement could be gained by changing the 10W-30 from CK-4 to FA-4. Mike Roeth, head of the North American Council for Freight Efficiency, says that fleets currently using SAE 15W-40 engine oils can secure one of their fastest returns on investment simply by capturing the fuel savings of lower viscosity oils.

One concern voiced by many in the industry is that lowering HTHSV limits may result in reduced durability. At the ICIS World Base Oils & Lubricants conference in London in 2016, Anders Pettersson of Volvo Group assured listeners that potential issues with oil film thickness, engine wear and lower oil pressure have been addressed and can be managed successfully. Pettersson based his conclusions on the performance of oils with 2.6 cP in the field and in Volvos new T-13 engine test. In fact, the European OEMs are all factory filling their engines with SAE 10W-30 and lower engine oils meeting Euro VI emissions limits. And truck and engine builder Iveco factory fills with an SAE 0W-20 oil having 2.1 cP HTHSV.

In North America the fuel economy benefits of lowered HTHSV along with good durability are being demonstrated in ongoing field tests, track trials, chassis dynamometer work and engine stand tests. With Decembers introduction of the API CK-4/FA-4 category, all North American factory fill is SAE 10W-30 CK-4 (or its proprietary equivalent, such as Mack Trucks EOS-4.5 oil). The exception is Daimler NA, which recommends SAE 10W-30 FA-4 as both factory fill and service fill.

The introduction of the CK-4/FA-4 category also sparked a general extension of oil life. Broadly speaking, all of the major engine builders have added 5,000 to 15,000 miles to their drain interval recommendations for equipment in all types of operations with the new oils, based on 2017 greenhouse gas mandates.

API CK-4 and FA-4 are identical in all aspects except HTHSV. CK-4 continues with the historic SAE J300 standard of 3.5 cP minimum HTHSV, to allow total backwards compatibility with API CJ-4 and earlier oils in any engine. FA-4s HTHSV is 2.9 to 3.2 cP, which effectively eliminates backwards compatibility. Some OEMs even are offering limited backwards compatibility, but for most pre-2016 model year vehicles, its expected that owners would stay with CK-4 products.

All of this sounds good, but some disconnects must be resolved. As Volvos Pettersson pointed out, there is a body of evidence indicating that lower viscosity results in better fuel economy. This is the result of reduced internal friction in the base oil and reduced hydrodynamic losses. Likewise, GHG emissions are reduced with lowered viscosity, a direct result of improved fuel economy.

Besides the durability issue, another question arises from the move to lighter weight oils: the potential for higher oil volatility, which translates to evaporative losses, oil thickening and shorter life. How do these issues get resolved?

Where durability is concerned, CK-4 and FA-4 offer improvements in several performance areas versus CJ-4. Oil oxidation resistance, aeration control and fuel economy are all improved with only a marginal reduction in soot control performance. However, soot control is less important now that on-road diesel fuel contains less than 15 ppm sulfur.

Volatility is a more difficult issue to resolve. It is an inherent property of base oil and cannot be modified or treated with additives. It is controlled by the boiling range of the base oil cut. For any given base oil viscosity, volatility varies by the breadth of the boiling range and by the chemical structure of the base oil. API CJ-4s limit on evaporative losses (per the ASTM D5800 Noack volatility test) is 15 percent max. For CK-4 and FA-4, its 13 percent max.

Controlling base oil volatility by narrowing the boiling range results in significant refinery yield losses since removing the more volatile front of the cut must be matched by removing some of the back of the cut, in order to maintain the same viscosity.

Base oil refinings influence on volatility is shown in the table on page 27, which compares the typical Noack volatility range for various base oil groups. As you can see, the key to lowering viscosity while maintaining volatility limits is to use higher volumes of Group III and IV base stocks.

Group III base oils offer other advantages. According to Mike Brown, vice president, technology at SK Lubricants Americas, Group III base oils feature low aromatics for better low-temperature oil flow; higher isoparaffins, which boosts viscosity index and lowers volatility; fewer chemical impurities, and a stable chemical structure. These latter properties are key to additive response and to improving oxidation and thermal stability.

Of course, proponents argue that Group III and Group IV base oils are a solution to the volatility question. But the solution comes with added cost, which engine oil marketers can find difficult to pass along to customers.

In addition, Group III customers face steep testing costs under APIs Engine Oil Licensing and Certification System, Document 1509, which defines the test requirements and limits for active engine oil categories. Annex E, Base Oil Interchange, lays out a process for utilizing existing data to effectively reduce the number of tests needed for an oil approval. This system uses the known properties of the various base oil groups to compare test results and determine whether or not a particular test is required.

The advantages of this process are that test program costs are lowered, supply flexibility is increased and there is greater cost containment. The drawback is that while there are reams of data to support interchange for Group I and Group II base oils, theres virtually none for Group III. (See Why is Group III Interchange So Hard? in the January 2017 issue.)

The cost of running the full battery of CK-4 tests can exceed $1 million, and eight of the 10 engine tests must be rerun if a change of greater than 10 percent of the original base oil mix is made. Once a formulation has been approved, this discourages base oil interchanges. The net effect is that program costs are much higher, Group III producers can stall in their efforts to penetrate the heavy duty engine oil market, and new producers have only limited access to this lucrative market.

Despite these hurdles, Group III base oils have seen expanded use to meet some of the more stringent requirements of newer engine oil categories, and the signs appear favorable for continued growth.

The signs all appear to be aligning. First, OEMs are designing their engines around lower viscosity oils, to help meet the new and more stringent emissions and fuel economy targets.

Second, the lower viscosity grades such as SAE 10W-30, SAE 5W-30 and even SAE 0W-20 are growing at the expense of traditional 15W-40 and monogrades.

Third, there are new oil specifications in both North America (API CK-4/FA-4) and Europe (ACEA 2016). Both specifications improve on fuel economy and are designed to handle any durability issues, which appear to be under control.

And fourth, it appears that there is ample Group III base oil available for current demand. Currently there are over 20 manufacturers of Group III base oils worldwide, and more projects are on the drawing boards.

However, the final piece of the puzzle-base oil interchange-is missing and needs to be established if Group III base oils are to achieve greater velocity in the heavy duty vehicle marketplace. This will allow blenders and additive suppliers a wider range of sources, and have a positive impact on costs and demand.