PC-11 Team Ponders New Viscosity Grade

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PC-11, the heavy-duty engine oil category upgrade being developed by diesel engine manufacturers and the lubricants industry, continues to make progress towards its April 2016 market debut. Meeting last week in Chicago, the New Category Development Team voted on the most critical tests that need to be included in the coming category, and also debated whether a new SAE viscosity grade might best ensure that these oils deliver their promised fuel economy in diesel trucks.

One of the primary tasks facing this group, which is chaired by Dan Arcy of Shell, was to agree on the slate of engine tests that should be included in the oil category. Three new engine sequence tests had been proposed, one each from Mack/Volvo, Caterpillar and Daimler.

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Sponsors of Macks T-13 test for thermal stability and oxidation and Caterpillars aeration test said these tests were ready for inclusion in PC-11, and both were voted in to the new category. Both tests already had the support of the American Chemistry Council, which represents lubricant additive companies.

Daimlers DD13 test, which is intended to measure piston and liner scuffing wear, presented a more knotty issue. The additive companies had not accepted this test yet, and the engine manufacturers themselves acknowledged that its reproducibility and repeatability are not ideal. Although Daimler expressed confidence that the test can be ready in time for PC-11, it asked for more time to complete its development work, so the New Category Development Team voted not to include the DD13 at this time. It still could be added later.

The accepted tests now will move towards a precision matrix, which involves repeated runs of the fired engine tests – a very expensive proposition. Steve Kennedy of ExxonMobil, speaking for the PC-11 Funding Group, advised the meeting that only about $2 million to $2.5 million is available to defray matrix test costs, and his group hopes to get API, ACC and EMA to share equally in the expense. If EMA, the Truck and Engine Manufacturers Association, would contribute more, so would API and ACC, he believes. Two independent engine test laboratories, Southwest Research Institute and Intertek Automotive Research, also said they will try to fill a gap in funding by providing discounts of up to 10 percent on the matrix tests.

The meeting also wrestled with the issue of how best to differentiate the new oils for consumers. It has been known for a while that PC-11 will actually be two oil categories. PC-11A will cover current viscosities like SAE 15W-40 and will be backward compatible with earlier oil categories, including todays API CJ-4 oils. PC-11B will address lighter diesel grades, such as SAE 5W-30 and 10W-30, and enhance their fuel economy contribution by focusing on their high-temperature high-shear viscosity. These lighter weight oils would be suitable for future diesel power plants, beginning with the 2016 model year, but not for older engines.

The American Petroleum Institutes Lubricants Group in September had discussed the ongoing question of how to most clearly label the difference between these two specifications. For PC-11A, the Lubricants Group is comfortable with a likely designation of API CK-4, which continues the current progression of letters associated with its heavy-duty or C category. For the PC-11B category though, discussions centered on how to establish an evergreen category while minimizing the number of characters, and while clearly differentiating between PC-11A and PC-11Bs distinct viscosities.

The New Category Development Team took up this discussion at their Jan. 30 meeting. There seems to be little debate that PC-11A will continue to have a minimum 3.5 cPs HTHS viscosity limit, as is the case with CJ-4 and earlier oil categories. This provides the needed backwards compatibility for existing engines in on- and off-road applications. However, there is a recognition that SAE XW-30 oils should provide fuel economy benefits versus SAE 15W-40, and engine builders want to wring as much fuel economy as they can from the new oils.

Hence, for PC-11B the goal is to gain fuel economy without sacrificing engine durability. One way to achieve this, the meeting heard, may be with a new viscosity grade tentatively referred to as SAE 26, which would be defined using either HTHS viscosity between 2.9 and 3.2 cPs or by kinematic viscosity of 9.3 to 10.5 cSt at 100 degrees C. This might result in a more limited backwards compatibility which would be OEM, engine and application dependent. Pursuing this idea will also require drafting a formal proposal to SAE to amend its engine oil viscosity classification system, SAE J300. This issue should go to APIs Lubricants Group for action, the development team decided.

The upside of a new SAE grade would be even better fuel economy than current SAE 15W-40 while being distinctly different, advocates said. It also would allow the API category (CK-4) to be uniform across all grades, allow the performance nomenclature to remain evergreen, and open the way for subsequent categories (such as CL-4 and beyond) to cover additional heavy-duty viscosity grades such as SAE XW-20. This scheme also maintains the naming consistency of the other previous categories. For consumers, it means that they can continue to order products by brand name and viscosity with confidence of getting the oil that their vehicles need.

The NCDT meeting also discussed the actual nomenclature of the PC-11 category, given the inclusion of both higher and lower viscosity products. After a review of seven options, the group felt that two might be suitable. One would be to use API CK-4 as the name for both higher and lower HTHS viscosity products – with the proviso that the former would be backwards compatible while the latter would not. The other proposal, and the one that seemed to garner the most support, is to call the higher viscosity product CK-4 and the lower viscosity product DK-4. The same caveats on backwards compatibility would hold, with the D version offering a parallel path and coexisting with CK-4. The issue next goes back to APIs Lubricants Group for review.

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Regulations Specs & Testing    Specifications