Automotive Lubricants

The PC-12 Picture Becomes Clearer


The PC-12 Picture Becomes Clearer
© Sergey Terebov


Back in December 2021, the questions about PC-12 were flying around like a swarm of bees looking for a new hive. The New Category Evaluation Team was in conversations to decide what and when we would need to address the next generation of heavy-duty engine oils. As I write this column in late January, the needs and wants are becoming clearer. In December I was concerned that there would be more tests proposed while the existing tests would continue. Kind of like Ronald Reagan’s famous quip that the nearest thing to immortality is a tax.

Below are some of the necessary changes for PC-12. Some of them are pretty similar to what we have now.

The viscosity grades are the same. The current CK-4 category has a minimum high temperature, high shear viscosity limit greater than or equal to 3.5 centiPoise, so there is no change there. The current FA-4 fuel economy viscosity covers only XW-30 engine oils at 2.9- 3.2 cP, but PC-12 has added XW-20 oils greater than or equal to 2.6 cP. This may cause a bit of grief within the heavy-duty market. After all, that is a pretty low viscosity limit for a diesel-powered engine. 

However, European vehicle manufacturer IVECO has been specifying SAE 0W-20 oils for several years. I became aware of this when I presented a paper on the future of heavy-duty engine oils formulated with Group III base oils at the 2017 ICIS World Base Oils & Lubricants Conference in London. At that time, IVECO had an 8.5% market share in Europe as well as a factory fill requirement satisfied by an SAE 0W-20 Euro VI performance product. 

PC-12 likely will not offer much change in the engine deposits area. A lot of that work was done for API categories CK-4 and FA-4. Deposit tests—which include the Caterpillar C13, Caterpillar 1N and Caterpillar oil aeration (COAT) tests as well as the Volvo/Mack T-11 test, which measures soot deposits—are in place. There may very well be changes in limits, however.

The biggest change in my opinion is the significant changes in wear tests. While API CK-4 and FA-4 had not one but four wear tests, PC-12 is targeted to have just three. That’s the good news. Two of the three tests are already developed and will need precision matrices developed for them. This is where it sometimes gets tricky, as was the case for the Sequence IVB. The tests must be able to pick winners and losers reliably, and sometimes the hardware or test conditions do not cooperate. The third test is the Mack T-12, which may be replaced or in some way be deemed equivalent to another test.

Soot dispersancy is an interesting situation. While soot in the oil can contribute to ring sticking, an increase in viscosity and problems with emission controls, the current ultra-low-sulfur fuels contain a maximum of 15 parts per million of sulfur, which actually makes soot formation less likely. Nevertheless, it will be necessary to find a way to measure soot levels reliably. The Mack T-11 has been the soot measurement tool for the API CK-4 and FA-4 categories but may be replaced by some equivalent test, just as the Mack T-12. 

The Category Life Optimization Group, commonly referred to as CLOG, has been tasked with determining what existing test can be used (with different limits or procedures) to give equivalent results. If it turns out that nothing will work, then a new test will need to be developed. A single test hardware set with different procedures might be a good choice, but that remains to be seen. 

Oxidation resistance is always a top concern on the part of the original equipment manufacturers. I’m sure that PC-12 is no exception. The current API CK-4 and FA-4 test procedure, the Volvo/Mack T-13, is the tool used to measure oxidation resistance. That test is currently under serious review, and CLOG is working toward finding an existing test method or recommending that a new test be developed. You’ll want to stay tuned to see what happens, since the T-13 has been the workhorse test method for some time.

Chemical limits have yet to be defined. That’s not a real surprise given that new federal regulations have yet to be established for emissions and other such things, and they probably won’t be until late this year. Current chemical limits for CK-4 and FA-4 are 1.0% maximum sulfated ash, 0.12% maximum phosphorus and 0.4% maximum sulfur. My guess is that all three may be reduced somewhat. The ash content will move, but not by much. Phosphorus will definitely drop, but to what level? I’m not sure. And sulfur will also become somewhat lower. As much as anything, that is the result of the greater use of Group III and synthetic base stocks combined with what I suspect will be lower-ash additive packages.

Elastomer compatibility is yet another procedure to be reviewed and probably updated. API CK-4 and FA-4 have test requirements for five classes of seals that are evaluated for changes in volume, hardness, tensile strength and elongation at break. PC-12 may have new seal materials and/or new limits on these parameters. That will be determined later.

Bench tests are a necessary part of any standard, and PC-12 is no exception. The current list of API CK-4 and FA-4 bench tests can be found in the latest iteration of API 1509, Engine Oil Licensing and Certification System. 

The ASTM D4683 High Temperature, High Shear Rate Viscosity test is a part of the SAE J300 viscosity classification system and represents the special limits set for SAE 10W-30 oils. The remaining tests are used specifically to measure copper corrosion, shear stability, volatility and foaming. The last test is related to the Mack T-11 (ASTM D7156) and measures low temperature, low shear rate viscosity with sooted oil. I am sure that these tests will also be a part of PC-12.

There is still one last, vital item to discuss: base oil interchange, commonly referred to as BOI. API 1509, often called EOLCS for short, defines base oil interchange as follows:  

“Not all base oils have similar physical or chemical properties or provide equivalent engine oil performance in engine testing. During engine oil manufacture, marketers and blenders have legitimate needs for flexibility in base oil usage. The API Base Oil Interchangeability Guidelines (BOI) were developed to ensure that the performance of engine oil products is not adversely affected when different base oils are used interchangeably by engine oil blenders.

“The API Base Oil Interchangeability Guidelines define the minimum prudent physical and engine testing necessary to ensure that engine oil performance is not adversely affected by substitution of one base oil for another. The Guidelines are based on actual engine test data, using different base oils, for both gasoline and diesel engine oil performance.”

To put it as simply as possible, base oils can be interchanged for both logistic and economic reasons. However, it is vital to note that the replacement base oil must perform the same as the base oil that it replaces. The guidelines are determined by various tests, SAE viscosity grade and API base oil group. In fact, the API base oil group designations were developed for this purpose. The grouping system has expanded well beyond base oil interchange and has become a de facto base oil definition system. Whenever there is a new category test method, BOI data are developed to ensure that this system is maintained.

So, there you have it. The march to PC-12 is now well underway. A process is in place, and schedules for team meetings have also been established. Team members have been identified, and the real work begins. If history is any gauge at all, this will run more smoothly than the development of PC-11 did, since we all learn from our mistakes.  

Steve Swedberg is an industry consultant with over 40 years experience in lubricants, most notably with Pennzoil and Chevron Oronite. He is a longtime member of the American Chemical Society, ASTM International and SAE International, where he was chairman of Technical Committee 1 on automotive engine oils. He can be reached at