Going back to my now well-worn and crumpled report on 1980 lubricant sales from the National Petrochemical & Refiners Association, I see that straight grades (such as SAE 20 and SAE 30) accounted for about 52 percent of U.S. engine oil sales. By 1990, the volume had dropped to around 28 percent and by 2000 it was 11 percent. In the final year for which NPRA published comprehensive volume data (2006), their share had dropped to almost 4 percent. In all years, total engine oil sales volume was on the order of 1 billion gallons per year.

During Decembers ASTM Committee D2 meeting in Anaheim, Calif., the American Petroleum Institutes heavy-duty engine oil categories that currently support straight-grade engine oils were declared to be obsolete. Effective at the end of 2009, API Categories CF-2 and CG-4 are gone. API CF-4 already had been dropped in June 2008. These categories, all introduced in the first half of the 1990s, died because the engines used to test for compliance are no longer available.

In addition, API CF is all but dead. Caterpillar, which loyally sponsored the single-cylinder oil test engine program for literally decades, has announced that the venerable Cat 1M-PC test will no longer be supported, and that Cat will no longer make parts available. The engine test labs indicate that they may have enough Cat 1M-PC parts for about six months – but after that, no more.

The only question was when to declare API CF obsolete. APIs Lubricants Committee balloted the issue and decided that December 2009 would be the end for licensing the category, after ExxonMobil asked for six more months to make an orderly transition to other specifications, especially outside the United States in parts of the world where CF is a recognized level of performance. So CF becomes obsolete Dec. 31, 2010.

A post-mortem exam of straight grades might begin with the question, what happened? What factors drove the steady change from monogrades to multi-grades, and what impact will this have on future sales of engine oil and related products? I want to explore this a bit and suggest what happened.

Why Theyre Dying

Single-grade engine oils were the only game in town until the mid-1950s, when the first viscosity index improved engine oils appeared. V.I. improvers were probably novelties when they debuted (Im not that old!), but as time went on, it became apparent that multigrade engine oils offered some benefits that were not available in straight grades. For one thing, it wasnt necessary to change oil grades for winter or summer service. They were a great sales tool, and gave oil marketers a chance to potentially improve margins.

Gradually, the auto manufacturers began to move to multigrade recommendations for their engines to gain the advantages of cold-start capability. GM owners manuals last referenced straight-grade engine oils in 1983 – and then only for use in warm temperatures. With the energy crises and air quality standards which came in the 70s, lower-viscosity engine oils became more important.

One technology that virtually demanded multi-viscosity engine oils was the four-cylinder engine. Since there is only one ignition stroke for each crankshaft revolution, starting and maintaining the start became a real issue. The starter could easily turn the engine fast enough to get it to start but, if the oil was too thick (read straight grade) the engine would immediately stall. The simple solution was to use multi-vis engine oils, which flowed well at both higher and lower temperatures. Since then, the push has been to lower and lower viscosity.

On the heavy-duty side, the change was slower in coming. The straight-grade market remained strong for a number of years, primarily supported by Detroit Diesels two-cycle engine market. In fact, it wasnt until DD introduced its first four-cycle engine series that it even recommended multigrade engine oils. There was some validity in this position, especially for the companys large displacement engines. I have seen power curves generated on 16V-149 Detroit Diesel engines that clearly showed a loss in power at higher output when multi-grade engine oils were used. (The V.I. improver in that case was a very shear-stable, gear-oil-type polymer in an SAE 25W-50 engine oil.)

However, the major over-the-road engine manufacturers all saw the advantages of multigrade engine oils. One of the clearest benefits to be identified was reduced oil consumption with multigrades.

On the face of it, that seems illogical (youd expect heavier oils to stay put) but it is true. Multigrades form a thinner – but still adequate – oil film on cylinder liner walls, so when the piston moves up in its travel, there is less oil to push into the combustion chamber to be consumed.

Theres another problem with straight-grade engine oils in heavy-duty applications: They tend to form more deposits than do multigrades. This is probably due to the use of higher-vis base stock cuts in straight grades.

Of course, the question of emissions also comes into play for the heavy-duty engine OEMs. Progressively more stringent emissions requirements make control of oil consumption critical since that is the most common oil-related contribution to emissions. Volatility is important, too, but the fact of reduced consumption due to oil film thickness is a critically important part of the equation.

Fallout for Other Products

So now we are down to 4 percent or less of U.S. automotive engine oil sales being straight grades. Some product applications that may still depend on these oils are certain transmission fluids, hydraulic oils, gear oils and general purpose lubricants. Each of these applications, if they havent already, will need to find replacement products and specifications to cover their former use of straight-grade engine oils, once they are finally obsolete.

Groups that write standards for gear oil and transmission fluid, for example, will have to review their existing standards to see if these orphaned applications can be covered by other specifications. Hydraulic fluids are already covered with proper viscosity grades. For general purpose products, users will have to search the product lines of oil marketers to find suitable substitutes.

Now it should be obvious that straight-grade engine oils will not disappear overnight. Oil marketers will continue to have customers for these products and, given enough volume, will continue to produce them. Some customers just dont want to change since they believe the product they buy is exactly what they want.

Take for instance the case I saw in the mid-1990s, of a major oil marketers niche-brand gasoline engine oil, which at best met API Category SC (circa-1967) quality. Its customers were adamant that they were not going to change. The oil marketer tried to convince them that a current oil (API SG at the time) would do just as well or better, but without success. For logistical reasons, the current SG engine oil was substituted for the niche-brand formulation (technically OK, because being backward compatible, SG covered SCs minimal spec) and the price was even raised above the current oil. Even then, some customers stuck with what they thought was the old SC- quality oil! As long as the volume was sufficient to continue to justify it, the brand didnt die. Only when volumes dropped below that level did the oil marketer cancel the brand.

What does that suggest oil marketers will decide to do with the straight-grade market? I suspect that straight grades will be made with the same dispersant-inhibitor (DI) additive package that is being used in their multigrade engine oil, just leaving out the V.I. improver. I also suspect that they will use the heavy-duty diesel additive package, rather than the one for passenger car engine oils, so that one set of blends can cover all engine types. Its even likely that gasoline engine straight grades will be eliminated, and only HD straight-grade products sold. It would solve a lot of logistics problems.

A New Specialty?

Certainly, straight-grade engine oil volumes will continue to fade. Some oil marketers will decide to drop them altogether, while others will continue to supply. One of the tenets of product life cycles is that as a product goes into the latter stages of its life, fewer companies will supply it. Only those which are well situated to serve a market will continue to produce the product. In addition, the price will probably go up due to fewer sources.

To illustrate this point, many oil marketers have de-emphasized or eliminated SAE 20W-50 engine oil from their product slates. Only a few still actively market this grade. The result is that, although the total U.S. volume of 20W-50 sold in 2006 was not large (about 24 million gallons), one or two oil marketers had a significant portion of that volume. Its now being promoted as a specialty engine oil grade for SUVs, high-output engines and off-road applications.

Straight grades are not going to disappear overnight. The questions will be how they are labeled, and how their performance level described. No current API category and more importantly no viscosity grade read-across on engine tests will support the licensing of straight grades. Although it can be done, no one will be likely to run straight grades in any engine tests, so it is unlikely that there will be any demonstration to confirm the products performance. That could open the door to some potential mislabeling. Another possibility is that labels could talk about API categories that are now obsolete. In any event there will be a period of adjustment before all of this gets squared away.

The bottom line is that progress always involves both gain and loss. Those out there who believe that straight grades are the only way to go will become increasingly anxious about the oil they buy, or even if they will be able to buy it at all. Astute marketers will make sure that straight grades will be available for those folks and in so doing may capture a small but loyal marketplace. For everything there is a season.