On Tue, 2008-03-04 at 09:10 +0000, gtr928 wrote:
I now have the oil test printed by Street Commodores in PDF, happy to
forward it on to interested parties. I have also forwarded it to one of
the moderators to await whether it will be placed on this site. It is
interesting if nothing else, draw you own conclusions.
I bought this issue (March 2006) of 'Street Commodores' when I was told of the oil test. I had some concerns about the application of this test to engine oils, and the way 'Street Commodores' applied the test. I actually bought an ASTM standard - which turned out to be a slightly different test but near enough - to evaluate 'Street Commodores'' application of the one it used. I formed the opinion that 'Street Commodores' was likely to be sued, potentially by all the oil companies but Royal Purple.
In particular, the range of the "Pressure Resistance" (1540 to 295,722 psi) beggared belief.
As I recall, in its next issue, 'Street Commodores' stated that it had been advised, and acknowledged, that the test was inappropriate for engine oils. I didn't buy that issue, so I won't speculate on what else may have been said, or the circumstances which prompted the backpedalling by 'Street Commodores'.
Anyone who reads the article should be aware that Royal Purple has cut and pasted what was printed by 'Street Commodores' to avoid direct comparison with Penrite Synthetic 5, the performance of which was equal, quantitatively, to that of Royal Purple 51 (and, to me, looked to have produced a less severe scoring of the test piece).
The Test
'Street Commodores' states in its introduction to the article:
The test we carried out on each of the oils is a measurement of the film strength properties of lubricating fluids, with the test equipment used being manufactured by Falex, a world leader in tribology test equipment. It is known in the industry as the Falex Lubricity Tester and gives a result very similar ‘Timken OK Load Rating Test’.
In the early 1930s, as a result of significant increases in horsepower and speeds in all types of industrial and automotive applications, extreme-pressure lubricants became popular. However, there was no standard to obtain comparative data on these lubricants.
In response, Timken engineers developed a lubricant test machine, which provided an economical and reliable means to determine the film strength characteristics of lubricants. In 1935, the company began producing and selling lubricant test machines. The lubricant test quickly became an industry standard.
The maximum load – in pounds – a lubricant could withstand without
failure due to breakdown of the lubricant film became known as the
‘ Timken OK Load’ rating and is still an industry standard today.
Serious product testing is conducted according to internationally-recognised procedures to ensure that valid comparisons can be made, even when similar products are not tested side-by-side. The pre-eminent standards authority in many fields, including tribiological testing, is ASTM International. (ASTM stands for American Society of Testing and Materials.) Even the ACEA, the European equivalent of the American Petroleum Institute (the API which specifies oil ratings like SM and CJ), utilises ASTM standards for many of its tests.
The standard I acquired is ASTM D2782 "Standard Test Method for Measurement of Extreme-Pressure Properties of Lubricating Fluids (Timken Method)". The D2782 test apparatus differs from that used by 'Street Commodores' in that the rotating "test cup" is lubricated by gravity (ie from above), rather than having its lower edge rotating through an oil bath. Other than that, it appears to be the same.
ASTM standards specify the design of the test apparatus, the test pieces and the test procedure, including (in this case) the rate of load increase, as each test load is applied, to avoid premature breakthrough of the lubricant film. Standards also specify repeatability and reproducibility requirements.
The tests - and test apparatus - used by 'Street Commodore' and that specified by ASTM D2782 are intended to be applied to much heavier lubricants than the engine oils tested. ASTM D2782 states:
NOTE 1—This test method is suitable for testing fluids having a
viscosity of less than about 5000 cSt (5000 mm2/s) at 40°C.
The kinematic viscosities, at 40 degrees C, of the oils tested ranged from 73.2 cSt for the Motul 0W-40 to 162 cSt for the Penrite Synthetic 5 (5W-60). Royal Purple did not state the viscosity grades for "Racing 51" but, based on 'Street Commodores'' observation that it resembled a 20W-50, and the specs published by Royal Purple for its 20W-50 early in 2006, its kinematic viscosity at 40C probably was about 170 cSt.
While the standard does not preclude the extreme pressure properties of such light oils, the facts that the test load is applied in two-pound increments, and scoring occured at a 2 lb load when several oils were tested, indicates that the test apparatus is insufficiently sensitive to properly test these oils. The standard includes several tables of example test data to illustrate the application of the repeatability and reproducibility requirements, and the VARIATION between tests of the same lubricant on the same machine of more than 8 lb appears to be not only acceptable but typical.
Given that 'Street Commodores' appeared to test each oil only once, any unevenness in the application of the load could have caused premature breakthrough of the lubricant film and, consequently, not be an accurate representation of that oil's extreme pressure capability.
The use of the oil bath method of lubricating the test area (via the rotating "test cup" (ie wheel) discriminates against oils of lighter kinematic viscosity. Absolute viscosity is defined as a fluid's resistant to shear (sliding over itself, ie its resistance to flow). Kinematic viscosity is the fluid's absolute viscosity divided by its density. This property indicates the fluid's resistance to flow under its own weight, whether by gravity or centrifugal force or both combined.
ASTM D2782 requires the test cup, which rotates through the lubricant bath and against the test piece positioned above it, to rotate at 800rpm and against the test piece at 123.71 metres per minute.
The lower the kinematic viscosity of a lubricant, the greater its tendency to drain from the test cup, and to be thrown from it due to centrifugal force (rotational inertia).
IMHO, testing oils whose kinematic viscosity covers a range of about 250 per cent of the lightest one, yet represents the results as if they were comparable, is not a fair nor valid comparison.
Having said that, the 'Street Commodore' test results may be indicating that Penrite, Valvoline and Royal Purple had continued to use ZDDP, when other brands had discontinued or minimised its use (bearing in mind that no defensible conclusions can be drawn on the basis of a single test run). The ACEA "A" specifications (for gasoline engines) limit phosphorus content to 0.1 per cent by mass. Until recently, only Penrite and Valvoline revealed the phosphorus content of its oils at all, and only Valvoline their zinc contents. (Valvoline has now dumbed down its online product information for markets outside the US, so you have to ring it to find out the specs for its locally-marketed products.) Back in 2006, for several of its oils, Penrite limited their phosphorus content to 0.095 per cent, almost certainly to enable it to claim compliance with ACEA gasoline engine ratings.
STRANGELY, in the past few months, some lubricant manufacturers have got ZDDP religion, and seem to be falling over themselves to promote their zinc and phosphorus contents, and even trumpet that particular lubricants do NOT meet API SM and ACEA standards.
I wonder whether this has been brought about by the outcry over unprecedented engine wear on numerous classic car web forums like Rennlist?