Heavy-duty Tests Scrutinized


Engine tests are the most expensive and time-consuming parts of engine oil specifications, so its no surprise that developers take time to consider how well those tests serve their purpose and whether any of them can or should be eliminated.

Such questions are being raised now as part of the industrys review of the newest heavy-duty diesel engine oil categories, API FA-4 and CK-4, which were launched in December. There appears to be significant sentiment that some tests should be retired either because they are no longer necessary or because it is becoming impractical to maintain them. The challenge, in some cases, will be to develop new tests to replace them.

On March 28, APIs Diesel Engine Oil Advisory Panel discussed some of these issues in a meeting held in conjunction with ASTMs Heavy Duty Engine Oil Classification Panel. The Diesel Engine Oil Advisory Panel concluded that API should create a Category Life Oversight Group, partly to consider what should be done about tests.

Lube Report conducted subsequent interviews with numerous individuals who attended the meeting about the discussion and their own sentiments. Those comments, given on condition of anonymity, are the basis of this article.

CK-4 and FA-4 include nine engine tests: one primarily for oxidation resistance; one for air entrainment; another for dispersancy; two for deposit control; and four for wear resistance, although they may be used to measure other parameters in some cases.

Among the tests cited by industry sources as candidates for removal is the Mack T-11 test from the API FA-4 category. One source said it seems tenuous because it was developed to address a particular need related to soot generated in Mack ASET (Application Specific Emissions Technology) engines, which were introduced in 2002 but discontinued a couple years later. In addition, the T-11 limits are based on soot levels up to 6.7 percent in the engine oil.Thanks to better combustion control and high pressure common rail – a fuel injection system found in modern diesel engines – its uncommon today for oils to contain more than 2.5 percent soot when drained. For these reasons some sources say the T-11 could be discarded or its soot cap lowered.

Some say the industry could also try to eliminate a wear test that it attempted to replace for the new categories – the Mack T-12 test for piston ring and liner wear. Originally the developers of FA-4 and CK-4 intended to replace the T-12 with a new test, the Volvo T-13, which was also meant to test for oxidation. However, the industry was unable to generate ring/liner wear in the T-13, so category developers kept both tests.

During the development of the DD13 scuffing test, Daimler was also not able to create ring/liner scuffing and ended up using rings without chrome coating in its test. This has led some to conclude that modern engines do not suffer ring/liner wear and that the T-12 could be eliminated.

Some industry sources have recommended eliminating the Roller Follower Wear Test (RFWT). It is a relatively low cost test, but is based on a 1980s GM design that is long out of production and not representative of todays technology.FA-4 and CK-4 also include two other tests – the Cummins ISB and Cummins ISM – that gauge ability to prevent valve train wear in sooted oils, and some observers contend the RFWT does not assure performance not seen in the Cummins tests.

One industry source said that some tests are getting long in the tooth and won’t make it to PC-12, the next heavy-duty diesel oil category.He cited several tests – the Cat 1N, the RFWT and even the Cummins ISM – that use older hardware. As engines and replacement parts to support these tests become more challenging to acquire, OEMs have added incentive to reconcile their relevance – especially when new tests enter the scene. At the same time, there is incentive to keep tests that are still relevant because of the cost of developing replacements.

The topic of how to reduce the number of existing tests is especially compelling since more tests are on the way. DEOAP and HDEOCP discussed the fact that Ford has developed a 6.7L diesel wear test and that Daimlers new DD13 Scuffing Test has been standardized. Neither of those tests were ready in time to be included in API CK-4/API FA-4, but they are viewed, at least by their sponsors in each case, as critical to defining the performance of oils used in their engines.

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