SAN DIEGO – Is it time to rethink engine oil viscosity to allow multigrades even lighter than today’s SAE 0W-20 oils? Is there a technical need for such exotic blends as SAE 5W-10 or 5W-5, or even 0W-0? That’s the puzzle facing a task force which met here last week during the SAE Powertrain, Fuels & Lubricants meeting.
The SAE J300 Engine Oil Viscosity Task Force has been considering the addition of some lower-viscosity, non-winter grades, which automakers want to help address their need for fuel economy. Non-winter grades currently stop at SAE 20, with nothing lower, and changing that will require writing new viscosities into SAE J300, the document that defines engine oil grades.
The task force, which is chaired by Chris May of Imperial Oil, had issued an exit poll on the subject to interested parties at last summer’s ASTM meeting in Kansas City, and reviewed the results here on Oct. 26.
The poll covered three possible grades, SAE 5, 10 and 15, and offered three possible alternatives for defining them, as follows:
1. Add SAE 10 and SAE 15 grades with minimum high-temperature/high-shear viscosities of 2.0 mPas and 2.3 mPas, respectively. They would have the same lower and upper limits on kinematic viscosity at 100 degrees C as the current SAE 20 grade (5.6 mm2/s and <9.3 mm2/s).
2. Similar to Proposal 1, but adds an SAE 5 grade with a minimum HTHS of 1.7 mPas. Studies by SAE’s Low HTHS Working Group have indicated that the kinematic viscosity of this grade would have to be less than 5.6 mm2/s; for the purposes of the straw poll a minimum 4.1 mm2/s was used, equivalent to the current SAE 10W grade.
3. Use the same HTHS minimums as in Proposal 2, but incorporate separate kinematic viscosity limits for each of the new grades (with SAE 5 having a minimum kinematic viscosity of 4.5 mm2/s), based upon blending studies conducted by the Low HTHS Working Group.
The poll’s results were not definitive. While all three concepts drew interest, none of them elicited overwhelming support. At last week’s meeting, Ford commented in writing and Shell made a presentation on possible ways to bring consensus to the subject.
Ford stated pretty emphatically that it didn’t want to see overlaps in kinematic viscosity at 100 C between grades. It believes that having common KV100 limits for the proposed grades could cause problems with certain engine components that use engine oil as a hydraulic fluid. The automaker’s own data from blend studies using different base stocks show that it is possible to blend to a separate KV100 limit with appropriate HTHS viscosity limits, wrote Ford’s Ron Romano.
Romano also expressed some concern that the new grades will be confusing to engine oil consumers, since some “W” grades and non-W grades will have the same number; for example, both 10W and 10. This invites the risk of 10W-XX being used where XW-10 might be recommended, and vice versa. The same would hold true for other viscosity grades (e.g. 5W-XX and XW-5). Romano suggested it may be possible to resolve this concern using a different numbering system.
Bob Sutherland of Shell Lubricants also presented data to show how the viscosity grades overlapped both on KV100 and HTHS viscosity, as demonstrated with blends of different base stocks including synthetics as well as various viscosity index improvers. Shell’s data mirrored Ford’s in many ways and seemed to show that two grades rather than three would be most workable.
Shell proposed using HTHS viscosity to define the grades, and having only two grades below SAE 30 rather than three or four. One of its concerns is that with more than two grades, the limits are so compressed as to make blending to the proper grade difficult.
The company agreed to review its data with regard to blend and composition details so the rest of the task force could replicate the tests to see how their results aligned with Shell’s numbers.
In written responses, Honda offered a proposal for setting HTHS viscosity limits by grade and asked for an SAE 0, while Toyota stated a concern that engine wear might well increase if HTHS viscosity dropped below the range of 2.3 to 2.4 mPas.
Valvoline’s Thom Smith also expressed concern over multiple viscosity grades having overlapping kinematic viscosities, and questioned the need to add viscosity grades at this time. The oil marketer believes the industry should not risk introducing grades that may not meet future needs before those needs are clearly defined.
Smith indicated that his company would prefer to delay any decision until after the task force’s proposal is published (as SAE paper 2010-01-2286, “Extending SAE J300 to Viscosity Grades Below SAE 20”), but at this time Valvoline doesn’t particularly like any of the proposals.
At the end of the day, the task force decided that ILSAC, the lubricants committee representing North American and Japanese automakers, should better define the need for new low-vis grades before SAE pursues this any further.