Back in the mid-to-late 1970s, the idea of a mixed-fleet or universal engine oil was really catching on. The U.S. military had led the way with a specification for universal oil that dated to 1964. The idea was to make it easy for commercial fleet operators to carry only one product that was suitable for both gasoline- and diesel-fueled engines. The American Petroleum Institute helped out by allowing licensees to show both C (heavy-duty) and S (light-duty) categories on qualifying products, such as API CD/SE or API CD/SF.
Twenty years later – by which time ILSAC GF-1 gasoline engine oils had appeared in the market and API CH-4 diesel engine oils were moving into place – the automakers top concerns were emissions systems and fuel economy. Some OEMs started lobbying against universal oils and they havent stopped since, even though many customers love the one-drum convenience of these products.
What made the idea so appealing then and so difficult now?
Prior to 1970, the OEMs all had their own variations on passenger car engine oils. All of them met what was called API MS (for Motor Severe) while the heavy-duty folks had API DS (Diesel Severe). However, most OEMs had some additional hurdles or tests that were theirs alone; for example, the Ford Falcon rust test.
The first categories to become part of the modern motor oil story were API SD and CD. Both these categories were created in 1970 to describe the fighting-grade engine oils that existed in the marketplace. The obsolete oils of the day were dropped into the reject bin, as API SA, SB or SC. When I went to work in 1974 at Edwin Cooper (now Afton Chemical), we already were developing API SE oils, and six years later at Pennzoil, we were pushing for API SF oils.
There were engine tests for each of these categories but there was no oversight of the tests and test conditions were able to be manipulated. Dont get me wrong here – there was no overt dishonesty, just the recognition that within the test parameters it was possible to make a test run mild.
One example of this is the Caterpillar 1H. At Edwin Cooper, we noticed that when this piston-deposit test was run in the winter, it tended to be a bit less severe. When it ran in the summer, it was more difficult. We figured out that the humidity of the intake air affected the test results. That was a parameter that wasnt controlled by the Cat 1H tests procedures… so we did it ourselves.
(Some old-timers also remember the battle cry of Give us the easy engine! That referred to engine test stands in the contract laboratories which were known to run a bit mild. If you wanted to pass a test, you had a better chance with one of these engine stands. The American Chemistry Councils Code of Practice put a stop to this ploy over 20 years ago. But I digress.)
In the late 70s and early 80s – just like today – there were many fleets with mixed gasoline- and diesel-powered equipment. Maintenance needs called for two different engine oil types, and the fear was that the wrong oil (primarily S-series gasoline engine oils) would be put into diesel engines and would be unable to handle what was then 1 percent sulfur fuel. If we could only make an oil that met both the S-series requirement as well as the C-series requirement, we would be foolproof.
The engine tests required for API SE passenger car engine oil were the Labeco L-38 for bearing corrosion and oxidation, plus shear stability for multigrades, the Sequences IID (rust), IIID (high temperature oxidation) and VD (sludge) engine tests, and some bench tests. For API CD diesel engine oils, the requirements were an L-38 and Caterpillar 1G2. There were no restrictions on phosphorus content, total base number or sulfated ash. Typically then, these oils had phosphorus levels around 0.13 percent, sulfated ash as high as 1.5 percent and TBN levels in the 10-14 range, as well as the requisite engine test results.
The only fly in the ointment was Detroit Diesels requirements. Detroit Diesel sold 2-stroke cycle engines, of a much different design than the 4-stroke models available from all of the other manufacturers. The primary effect of these differences was that DD engines needed an oil with 1 percent maximum sulfated ash and TBN levels around 7. Formulation-wise, they also had an appetite for bright stock as a lubricity agent, and were predominantly monogrades.
The additive suppliers were pretty smart and figured out how to make multigrade engine oils that would meet the Detroit requirements. API also helped by creating a category specifically for 2-cycle engines. The industry knew these as API CD-II and CF-2.
Detroit Diesel notwithstanding, universal oils became a part of the marketplace and were mainstays for a number of years. However, there were concerns voiced, especially whenever performance requirements advanced. As emissions and fuel economy became more important to the automakers, the levels of phosphorus became an issue.
Ford presented papers at SAE and elsewhere showing that phosphorus in the form of zinc dialkyl dithophosphate produced a compound called zinc pyrophosphate which blocked the honeycomb structure of exhaust system catalysts, making them nonfunctional. The zinc story was made more complicated by the fact that the type of zinc used differed between S-series engine oils (better wear protection) and C-series oils (better antioxidancy).
When the ILSAC GF-series of gasoline-fueled engine oils were introduced, the automotive OEMs insisted that any universal oil must meet all of the requirements of the GF category, which differed from the API series primarily in emphasizing fuel economy. Sulfated ash was also a consideration, since high TBN wasnt really an issue for gasoline-fueled engines, and later, phosphorus became a target.
ILSAC GF-1, introduced in 1992, didnt have any phosphorus limit so there was still a window for universal oils, provided they met both current C and S category requirements. This was especially true for the heavier viscosity grades like SAE 10W-40 and SAE 15W-40 that were extraneous to the OEMs drive for fuel economy. All of GF-1s limits were shared by API SH – except for enhanced fuel economy.
When GF-2 came into existence in 1995, the paths began to diverge more. GF-2 phosphorus levels were limited to 0.1 percent max. GF-4 trimmed phosphorus in 2004 again, to just 0.08 percent max, where it remains.
Today, in Annex G of API Document 1509, the Engine Oil Licensing and Certification System, youll find the requirements for each viscosity grade for the current Service categories: SJ, SL, SM and SN. Youll also see some footnotes relating to universal oil that make some allowances for potentially conflicting test requirements. Notably, ILSACs GF categories, which are identified by the API Starburst Certification Mark, are not included in any of these adjustments.
In all cases from API SJ forward, and for all viscosity grades, Annex G says that if a commercial engine oil category such as CH-4, CI-4 or CJ-4 is shown first in the API Donut and there is no API Starburst logo on the product, then there is no requirement to pass the Sequence VG, Ball Rust Test, and Gelation Index test. That makes the window just a little bit bigger for universal oils to squeeze through.
There is some easing of other requirements, too, on a category-by-category basis:
In Category SL, the phosphorus limit of the ILSAC oils doesnt apply.
For Categories SM and SN, the phosphorus limit does not apply, and sulfur and TEOST MHT limits dont either.
However, for API SN there is the requirement that the sulfur and phosphorus limits associated with API CJ-4 must be maintained (i.e., 0.12% max phosphorus and 0.4% max sulfur).
There is a cautionary note that goes with all of these relaxations in limits, which reads as follows:
…these C category oils have been formulated primarily for diesel engines and may not provide all of the performance requirements consistent with vehicle manufacturers recommendations for gasoline-fueled engines.
The market introduction of API CK-4 and FA-4 heavy-duty engine oils at the end of this year raises the issue of just what adjustments will be made to accommodate the new categories. What may happen to the permissive footnotes in Annex G?
The current thinking is that the footnote that identifies test limits that will not be required will not apply to CK-4 and/or FA-4. APIs senior engine oil program manager, Kevin Ferrick, stated it pretty succinctly when he told me that marketers of API CK-4 and FA-4 oils that also wish to claim SL, SM or SN - or API SP when it finally sees the light of day – would not be allowed to exceed the phosphorus limits for those S categories.
Still, Ive heard from several major oil marketers who all say that universal oils have a continuing place in their plans. They all expect that they will be able to sell products meeting both gasoline and diesel engine requirements.
Im guessing that those smart additive suppliers have broken out the Harry Potter gear for their formulating wizards, who are hard at work on low-ash, -phosphorus and -sulfur oils that meet both the latest C category and S category test limits. Dont be surprised if something appears before long.
A key word got dropped from my opening paragraph in June: The Sequence VIII test measures weight loss in copper lead bearings, not copper bearings.
Industry consultant Steve Swedberg has over 40 years experience in lubricants, most notably with Pennzoil and Chevron Oronite. He is a longtime member of the American Chemical Society and SAE International, where he was chairman of Technical Committee 1 on automotive engine oils. He can be reached at firstname.lastname@example.org.