By: Steve Sturgess
In response to current and upcoming mandates on heavy duty diesel engine fuel economy, engine manufacturers are looking at ways to increase fuel efficiency and decrease internal losses in the engine.
A path to increased economy is to run the engine hotter. Decreasing losses includes using an engine oil that takes less horsepower to pump it. Both conditions are addressable by establishing a new oil formulation standard and that is what PC-11 is all about.
PC stands for Proposed Category and it will address the additional oxidation potential caused by higher temperature operation. Also, improved shear stability and improved oil aeration are addressed in the changing specification. New in this category discussion is reducing the base viscosity to make the oil easier to pump, reducing one of the “parasitic” loads on the engine. But the challenge is to do so without losing the engine protection that has been gained with the current generation of 15W-40 oils covered by the existing category CJ-4.
Once the final testing procedures have been agreed, and the target is December 2016, the category is no longer proposed: it will likely become CK-4 for the replacement for CJ-4 oils. But there is an added wrinkle that will call for an altogether different classification as well.
Currently, the new standard is being proposed in a split category for the first time. For now, the category is being developed as PC-11A and PC-11B. The first is a direct replacement for the oils currently in widespread use in diesel engines. It’ll be available in the same viscosity grades and oil types (conventional, full synthetic, synthetic blend) currently in use, though with the extra protection for the next generations of heavy duty diesels. And it will be “backwards compatible” to all current vehicles and engines. The new PC-11B engine oils will be available in lower viscosity grades and are designed primarily for next-generation engines. The aim is to help maximize fuel economy without sacrificing engine protection. But the PC-11B oils may have limited backwards compatibility and the labeling will spell out a warning that this is the case. Because they are new, it is likely they will be categorized as FA-4.
It appears the two categories can both have SAE 10W-30 viscosity grades so the consumer will have to make sure they are looking at the correct API performance category: CK-4, more viscous/thicker or FA-4, less viscous/thinner, depending on the engine manufacturer, model year and application. Oil companies, truck and engine makers are currently testing PC-11B, FA-4 lubricants in a range of applications to demonstrate that there isn’t any loss in engine protection associated with lower viscosities.
So that’s basically the task of the committee that’s setting the standards that the test procedures for the oil manufacturers and marketers will have to meet in order to put the American Petroleum Institute’s “Donut” on their packaging.
The Deeper Dive
Now we have to look deeper into the terminology to understand why these new oils can deliver the durability we have come to expect from high quality diesel engine oils. The term High Temperature, High Shear (HTHS) viscosity is associated with both PC-11A AND PC-11B and is another method of expressing viscosity. It is measured differently from the more familiar kinematic viscosity, which is used to identify the high temperature portion of SAE Viscosity grades.
HTHS requires measurement at higher temperatures than kinetic viscosity. But, like kinematic viscosity, the lower the number the “thinner” the oil. There’s been a lot of research that shows that HTHS is the measurement that is most highly correlated to fuel economy performance. Historically, there has been a limit in lube standards requiring HTHS viscosity cannot be lower than 3.5 centipoise. And that’s the paradigm that’s been broken with this new category. In order to offer fuel economy improvements, the research dictates a lower HTHS number is required. That is the essence of PC-11B low viscosity category. The low-viscosity limit is between 2.9 and 3.2 centipoise, where the conventional lube will continue to be 3.5 or higher.
Oxidation stability has to be enhanced for the next generation engines as they are likely to be operated at higher temperatures. Oxidation of the oil and additives doubles with each 10 degree rise in operating temperature and oxidation is one of the primary causes of oil breakdown. In developing the new categories, this must be taken into account.
Finally, aeration occurs when tiny bubbles are trapped in the oil and they impact the lubricants’ ability to keep metal parts from contacting each other by breaking through the oil film. There’s a new Caterpillar test in the battery of category requirements. Not coincidentally, the hydraulic electronic unit injectors (HEUI) developed by Sturman Industries; used by Navistar and Caterpillar was based on engine oil pressure. Hydraulic amplifiers generated injection pressure. Along the way, the high-pressure pumping would force air into the lube causing the oil aeration issues.
Testing Tells All
While the PC11 committee meets on a monthly basis, the oil companies are hard at work with the additive providers to build engine oils that will meet the upcoming standard with no loss of performance. Then, independent testing, conducted by companies like San Antonio-based Southwest Research Institute (SwRI) verifies that the lubricant does pass all the tests.
Companies such as Shell go one more step which includes real world testing for including oil consumption, wear performance and other performance testing in high-mileage engines. The engines are torn down at around 500,000 miles to measure the effects of different oil formulation to ensure no wear issues are present, especially in the lower viscosity PC-11B lubes. There are excellent photographs on the Shell website www.whatispc-11.com showing wear on different engines: Detroit DD15, International MaxxForce, Paccar MX, and Volvo D13. Inspection of cam lobes, main and rod bearing shells, small-end bushings and piston carbon deposits show no discernable difference between PC-11A, B and current CJ-4, indicating no sacrifice in engine durability. In fact, with the new testing and formulation there is a likely gain in engine durability and the torn-down engines could all go back into service for another 500,000 plus miles!
Shell’s site also gives a good idea of the testing that goes into the development of the new oils. For PC-11 the company will have had to pass nine regulated engine tests and rigorous testing in more than 400 vehicles in the real world across truck fleet, construction and agricultural equipment and diesel pick ups. In all, these vehicles will accumulate mileages that equate to 803 times around the world.
What It Means To You
If you’re running an older truck, then switching to the new CK-4, backward compatible oil in the same viscosity you use today. It’ll be that seamless and you’ll get the added protection from the latest formulation. If you’re running a really modern truck – especially if its factory filled with a 10W-30 oil, then you’ll need to consult an engine manufacturer’s rep to see if the latest FA-4 is approved for use. It may be, or it may be you’ll have to stay with the CK-4, again, at the grade you’ve been using which is presumably what the manufacturer called for when you acquired the truck.
But if FA-4 is approved, you can be confident that you have the equivalent engine protection but with the added bonus of a one to two percent improvement in fuel economy. And that’s well worth having at today’s fuel prices.
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