This share had been dropping for years, primarily because of the push to multigrade engine oils. That push is due to a desire by light-duty truck and automobile manufacturers to gain as much fuel economy benefit as possible. The heavy-duty truck market also has pushed for multigrade engine oils, due to their improved performance in engines with exhaust gas recirculation and other emissions controls, as well as improvements in fuel economy.

Single-grade oils seemed on their way to a quiet extinction. However, its never as easy as it seems. Recently, Dan Larkin, formerly the lubricants expert at Detroit Diesel and now an industry consultant, posed a question to the American Petroleum Institute. Since APIs Lubricants Group has declared the CF heavy-duty engine oil category to be obsolete, he wanted to know: What API category is recommended if a customer wants an API-licensed SAE 40 oil?

Larkin was particularly interested in what he could safely recommend for use in large marine engines such as ALCO or Fairbanks Morse engines, which specify API-licensed SAE 40 engine oils. He recalled that there had been technical issues with single-grade oils passing all the required tests for the newer categories, such as API CH-4 and higher, yet he noticed that some SAE 30, SAE 40 and even SAE 50 grades are licensed to the API CH-4 category. So he wondered, had there been some accommodations made for monogrades in CH-4? Or put another way, if I suggest an API CH-4 SAE 40, would that be a valid recommendation?

Hes not the only one whos interested in how current engine oil categories can address single-grade products. I also have received requests for guidance from Europe. One reader writes that the decision to eliminate the API CF category will result in single-grade oils being marketed with current API specifications such as CH-4; given that single-grade oils cant pass the CH-4 test requirements, what can he tell potential customers?

Some API category history is in order here. Lets go all the way back to 1955, when API category CD was introduced for certain naturally aspirated and turbocharged engines. In 1985 the CD-II category was established to take into consideration the unique needs of two-stroke cycle (2-cycle) engines, particularly Detroit Diesels.

In 1994, CD was replaced by CF, and CD-II by CF-2. This was due to a change in engine tests (from the Caterpillar 1G-2 to the Caterpillar 1M-PC). The application was for off-road, indirect-injected and other diesel engines including those using fuel with over 0.5 percent weight sulfur.

Meanwhile, the API CF-4 category had been introduced in 1990 as an upgrade from API CE (introduced in 1985) for both naturally aspirated and turbocharged high speed diesel engines. In 1995 the API CG-4 category was introduced for severe duty, high-speed, four-stroke engines using fuel with less than 0.5 percent weight sulfur and was for engines meeting 1994 emission standards. (Are we clear so far?)

1998 brought us the API CH-4 category for high-speed, four-stroke engines, designed around that years stricter emissions standards. CH-4 oils were specifically compounded for use with diesel fuels ranging in sulfur content up to 0.5 percent weight. Unfortunately for straight grades, some of this categorys required engine tests (such as the Caterpillar 1P and 1K, Mack T-8E and Cummins M-11) have a strong bias for monograde engine oils.

This is where the straight-grade issue became critical. Prior to CH-4s debut, it was possible to approve straight grades using the industry-accepted base oil interchange and viscosity grade read-across guidelines established by API in concert with ASTM and the American Chemistry Council (ACC). But the multigrade bias in CH-4 is so strong that the 1P and M-11 dont even include read-across guidelines for straight grades.

The type of base oil used also impacts engine test performance. API Group II base stocks perform better in multi-cylinder diesel engine tests, where the higher degree of saturation appears to help with control of soot loading in the oil. Multi -grade oils also seem to be superior in oil consumption control. One school of thought is that this is due to a relatively thinner film of oil on the liner, meaning less oil is swept into the combustion chamber on each upstroke of the piston and thus less oil consumed.

Of course, all was well as long as CF and CF-2 were current categories, and could cover the single-grade needs. That changed in late 2009, when Cat announced that it would no longer support the Cat 1M-PC engine test or produce any more parts for it. Since the 1M-PC was an integral part of both categories, the demise of the test signaled the end of APIs heavy-duty single-grade babies, as they were thrown out with the CF and CF-2 bath water.

However, as Dan Larkin and other sources point out, there are markets and customers who still require single grades and want products that meet API licensing requirements. SAE 30 diesel oil is an important category for some people, one oil marketer insisted plaintively. Am I missing something, or is API?

Is there a legitimate way to certify single grades for API CH-4, or will there have to be a shadow system that covers single grades with additive systems that are CH-4 level but cannot meet all of the API requirements?

I checked in with Kevin Ferrick, engine oil licensing manager at API in Washington, D.C., to get his take on the situation. While the issue has been discussed, he indicated that APIs Lubricants Group has shown little interest in developing any new category for single-grade oils, or even developing some sort of accommodation for them within current categories.

Greg Shank and Steve Kennedy were no more encouraging. Shank, who is with Volvo/Mack, chairs the lubricants group in the Engine Manufacturers Association (EMA); along with ExxonMobils Kennedy he co-chairs the Diesel Engine Oil Advisory Panel (DEOAP). Both men emphasized that modern heavy-duty diesel engines are designed for use with multi-vis engine oils. This trend has been going on for a number of years.

Kennedy pointed out that the DEOAP years ago discussed the concept of allowing oil marketers to license monograde oils using an additive package that is CH-4 qualified. The idea was that API would establish a CH category, and marketers could manufacture monogrades containing the same additive used in a licensed CH-4 multigrade; these oils then could be licensed with no additional engine testing. However, this concept did not gain enough support from oil marketers or OEMs to move forward at that time. The scheme resurfaced during some of the more recent discussions when the terminations of CF and CF-2 were being considered, and there was still no support, he said.

Kennedy also noted that there have been no changes or adjustments to CH-4 to accommodate qualification of monograde oils. Any monograde oil licensed as CH-4 would need to have supporting documentation consistent with the published requirements for this category.

Lets assume for the moment that the industry can get behind an accommodation for straight-grade engine oils that would fit into API CH or some other category (seems unlikely). What would it take to make this a fait accompli? Actually, there is a process that would allow for this, outlined in Appendix D of API 1509, the document governing the Engine Oil Licensing and Certification System. The process is designed for creating new, more advanced categories rather than back-filling any holes in the system. However, it would also work for a simple modification to an existing API category.

It is essentially a three-phase process. Phase one determines whether or not the request represents a real need. To begin with, anyone can request a new category. The DEOAP, which is a joint group supported by API and EMA, would appoint a team to review the request and to answer such questions as: What is the change and why is it required? When is it needed? What impacts would it have on engines, consumers and the environment? Are there tests available to evaluate performance? Do the perceived benefits outweigh the costs to develop the category?

If that goes well, then phase two begins. That is the category development process and is managed by a New Category Development Team. This team works with representatives from API, EMA, ASTM, ACC, SAE and other interested groups such as JAMA or CEC. Their goal is to coordinate the efforts of the various organizations in developing the new category.

When phase two has been successfully completed, phase three, category implementation, takes over. API and EMA working jointly through the DEOAP assure that all of the goals have been met and follow the API 1509 process guidelines.

From start to finish, this process could take anywhere from one to three or more years. That shouldnt come as much of a surprise to industry insiders but is probably a real eye-opener to everyone else. There is always give and take between the oil marketer and the engine builder. Oil wants reasonable costs and engine wants maximum performance. Consensus always takes time, as do engine test development and/or test review as well as data analysis.

Given the caveats and the response from industry, the questions that have been raised and the weak market demand, I think that any new single-grade category – API CH or whatever – will be a long time in coming. I sure dont see a monograde heavy-duty engine oil category in our immediate future.

So the obvious question is, what way is there to cover heavy-duty single-grade needs? For now, current existing formulations (additives and base stocks) which meet the now-obsolete CF specifications will have to stay around. Meantime, those engines calling for single grades must be evaluated for performance using modern multigrade oils. If they perform successfully, then the single-grade death spiral will be accelerated.

If they dont perform successfully, the various governing bodies (API, EMA, etc.) will have to go back to the drawing board. Any way you slice it, there will be a lot of time and money spent to resolve the dilemma.