Noack volatility test: A new set of upheavals
Just as it appeared the dust had settled on the somewhat controversial Noack Volatility Test, we are now faced with a new set of upheavals. The implementation of the Lubricant Test Monitoring System (LTMS) severity adjustment has helped moderate discrepancies plaguing the bench test in recent times, however, now we consider the prospect of new equipment to measure volatility.
The Noack Volatility Test was originally developed and used in Europe and is a critical measure of motor oil quality. The test determines the mass an oil loses through volatilization during high-temperature service. Results are reported as a percentage of mass an oil has lost during the test — the lower the percentage the better, as this demonstrates resistance to oil volatility and breakdown. The volatility limit for ILSAC GF-5 is 15%. ACEA and GM’s dexos specify a maximum Noack volatility limit of 13%.
Clearly, it is important for OEMs and the oil industry to understand the volume of oil lost from the engine by volatility. When customers complain about oil loss, more often than not it is assumed that the loss is related to the oil entering the combustion chamber because of poor mechanical condition of pistons or rings, as opposed to simple volatility. Still, manufacturers need to understand how much is going out of the tailpipe. A high volatility oil means less in your sump for lubrication, the oil becomes thicker and heavier, reducing fuel economy, and, of course, increasing emissions.
Greg Miiller, vice president of operations at Savant Group, and first vice chair of ASTM Committee D02, says his company is examining the nature of volatiles to understand individual components, and further appreciate environmental impacts. He notes that the test only considers the volume escaping out of the engine. Individual components are not currently measured as part of the ASTM D5800 Standard Test Method for Evaporation Loss of Lubricating Oils by the Noack Method.
ASTM D5800 has three different test procedures — Procedures A, B and C. The test equipment for Procedure A — which had been manufactured by PAC, a global manufacturer of analytical instruments — is not really used extensively anymore because of safety and environmental concerns. Procedure A involves the use of Wood’s metal, which is toxic because it contains lead and cadmium.
When Procedure B was developed by PAC to replace Procedure A, it gave different results compared to Procedure A, owing to a bias that required adjustment to produce equivalency. Many PAC Procedure A instruments have been replaced by their Procedure B instruments. As a consequence, the largest volume of volatility test equipment in the industry is Procedure B.
The Selby-Noack equipment, created by Tannas Company, which is part of the Savant Group, closely matches Procedure A but does not use Wood’s metal. Because it is a very different equipment design, it was included in ASTM D5800 as Procedure C.
ASTM D5800 analyzes oil to see how much of the more volatile components of the lubricant come off. It comprises a one-hour test at 250 degrees Celsius with a slight vacuum. A weight sample is taken before and after the test to determine volatility. In recent years there has been escalating concern about the repeatability of Procedure B. Miiller noted that, “the test method started shifting severe. We saw higher volatility results that were questionable.” Oils were failing when they shouldn’t have. Even reference oils started to show an increase in volatility. “It really upset the industry,” observed Miiller.
In an effort to make D5800 more useful for licensing and auditing engine oils, the D02.B0.07 Bench Test Surveillance Panel implemented a new strategy for LTMS monitoring. Using Exponentially Weighted Moving Averages (EWMA) of monthly calibration runs, instruments that exhibit a consistently severe bias receive a severity adjustment, while inconsistent instruments are excluded from the system. While a common approach in engine testing, this marks the first time this monitoring technique has been applied to a bench test.
To the independent observer, this seems akin to putting your finger in the dyke to halt the flooding. However, Valvoline, one of the first advocates for severity adjustments, says it is performing “pretty well.” Joshua Frederick from Valvoline, who is the chairman of the volatility section of the Bench Test Surveillance Panel D02 B7, reveals that prior to LTMS “25-30% of every calibration attempt failed, now it’s down to 5%. We are still excluding inconsistent instruments, while we’re providing equalizing severity adjustments for instruments that are consistently biased,” he further noted. ASTM has just passed a ballot through Subcommittee 6 to reference the LTMS system in the D5800 standard itself — closing all the loops.
These well-documented severity issues prompted Tannas Company, manufacturer of Procedure C instrumentation which correlated well with Procedure A, to develop a new range of equipment which could be modified to correlate with either Procedures A or B in assessing volatility. Miiller says that the new Noack S2TM equipment is “adjusted to give consistent Procedure B results without the need for LTMS, with the same basic configuration as the original Selby-Noack — but with improvements.” Enhancements include a pre-heated thermal well for consistent heat-up and to avoid long lag times, while maintaining the tune-ability of the equipment — a feature that is absent in the existing PAC product. If Noack S2TM reference value is slightly off, you can retune it back to a certified value. Miiller claims this provides improved accuracy and precision.
Noack S2TM equipment has been available to the market for almost two years but has not yet been involved in the Test Monitoring Center (TMC) reproducibility tests for volatility. In Europe, the Noack S2TM is in the process of getting approval as part of the equivalent L-40 Noack Volatility Test by the Coordinating European Council (CEC). Following two ‘round robins,’ or Inter-Laboratory Studies, the CEC approved the precision in May 2017 and is now making a decision on updating the test method to include the Noack S2TM.
On the other hand, ASTM has been grappling with the changes. Should the instrumentation become part of Procedure B or is an entirely different procedure required? A working group has completed the necessary tests, revised the test method, and concluded the mandatory research report — yet the product narrowly failed an initial ballot in Subcommittee 6, Section B — requiring minor remedial action.
However, an update to F+L Magazine on February 9, 2018, suggests that the Noack S2TM can no longer be accepted as Procedure B. During a recent workshop for the PAC equipment, a previously undisclosed algorithm for test length in the current D5800B was unearthed, which is proprietary information. The situation is still being investigated. A decision was made to make the Noack S2TM test method Procedure D — or D5800D — which was supported by ASTM. The caveat is that the results are considered equivalent to D5800B and this is clearly stated in the revised test method. Miiller says this proposed modification has been balloted and passed in March 2018.
It is now official that the Noack S2TM is ASTM D5800, Procedure D and is considered equivalent to Procedure B.