Truck News


Generating differences

CK-4 and FA-4 oils delivering better shear stability, longer drain intervals

Engine oil is as versatile as it is vital. Not only does it lubricate an engine’s moving parts so there’s no metal-to-metal scuffing, it also disperses heat.

Now it performs better than ever.

The CJ-4 oil category had been around for years when its replacement was officially introduced in December 2016, as equipment manufacturers prepared for the latest round of emissions-related rules. But this time there was no single replacement. Instead, the change gave birth to a pair of categories – CK-4 and a fuel-efficient FA-4.

The CK-4 oils are now the most widely used formulas on the market today, in part because they are fully backward compatible with former CJ-4 oils. In other words, you can pour CK-4 in older engines that once ran on CJ-4 without worrying about possible damage. Most engine manufacturers also use CK-4 oil as their factory fill, as equipment rolls off the assembly line.

While FA-4 offers the promise of better fuel economy, they are not always backwards compatible with legacy equipment. There are exceptions, though. Detroit engines are among them. Freightliner and Western Star trucks with DD13, DD15 and DD16 engines have been factory filled with FA-4 oil since January 2017. Models as old as those made to meet EPA 10 emissions standards can use it as well.

Other newer engines, such as Cummins’ X15, can use either CK-4 or FA-4 oils. “X15 on-highway engines have permitted FA-4 use. Key engine platforms are investigating FA-4 oils to understand their backwards compatibility,” says Autumnlynn Glass, engine fluids chemist and engine oil industry liaison with Cummins.

But the CK-4 formulas clearly seem to enjoy a significantly larger market share than FA-4.

“If the number of licences is any indication, there seems to be a greater desire for CK-4 at this point,” says Kevin Ferrick, manager of the American Petroleum Institute’s (API) engine oil licensing and certification system. So far, the API has certified 947 CK-4 products compared to 96 for FA-4, which is roughly a 10:1 ratio.

But asking whether CK-4 or FA-4 is a better choice would be a misleading question. The most important thing is to use the oil that’s better for your engine as per the OEM’s recommendation.

“I know it sounds like a very simple thing, but you’d be surprised how often we have this conversation with people,” Ferrick says. “There’s a reason why the engine manufacturer recommends a particular viscosity and performance level. I’m not sure you want your engine to be something that you use as a test.”

Relying on the manufacturer’s recommendations is precisely what Darryl Watkins, fleet maintenance manager for Commercial Transport Northern, did.

“I talked to the manufacturer [of the Paccar MX engine] about what we should be using. This is what they recommended and that’s what we switched to,” he says about the CK-4 that smoothly replaced CJ-4 in the fleet he oversees.

Better shear stability

While each has unique properties, the CK-4 and FA-4 oils share many attributes that better their CJ-4 predecessors.

For one, the new oil categories are thinner and offer better shear stability. The latter feature measures the oil’s ability to maintain a viscosity despite mechanical stress — something usually associated with higher operating temperatures. The categories are also formulated to better protect engines against oxidation, says Cummins’ Glass, referring to the oxidation stability of CK-4 oils.

The engines are also known to be “tighter” than models that came before them. Essentially, oil has to penetrate between moving parts that are moving closer to one another than ever before.

“Engines are built much more precisely. Their tolerances are much smaller because they [engine manufacturers] try to bring out as much power, as much efficiency as possible

from these engines,” API’s Ferrick says, referring to a focus on aeration control, which helps to reduce the threat of air bubbles in the oil.

With engine parts so close together, any air in the oil paths could lead to gaps in the all-important lubricating film, threatening the engine’s integrity.

Longer drain intervals

All these enhanced oil capabilities ultimately lead to longer drain intervals. The vital additives last longer. So drain intervals associated with CK-4 and FA-4 oils are up to 60% longer than those associated with CJ-4.

The exact improvement in terms of drain intervals will vary, for course, but they are real.

“For appropriate customers, based on their duty cycle, a 60% longer oil drain interval may be realistic. However, this may not be ideal for all engines and all customers,” Glass says.

A good real-life example comes from Sudbury, Ont., where Commercial Transport’s new Paccar engines show a 50% increase drain intervals, even in harsh applications, according to Watkins. “We went from 40,000 km to 60,000 km,” he says of the switch to CK-4 from CJ-4. “It just seems to work for us.”

Thicker is not always better

While the new oils are essentially thinner than the CJ-4 formulas they replace, even with the same viscosity grade, deciding on a thicker grade than the one recommended by a manufacturer would be a bad idea, Ferrick stresses.

“There is sort of this idea out there that thicker is better. In today’s engines, that’s not necessarily true. If it’s a heavier viscosity grade, the engine has to actually work harder. Its moving parts work harder because there’s a heavier viscosity grade, which is actually impeding the performance of the engine,” he says.

Cummins’ Glass agrees. “If there is an instance where a customer desires to make a viscosity grade change for improved fuel economy or cold weather performance, it is always recommended to consult the service literature,” she says.

That difference in viscosity may very well be why Commercial Transport’s Watkins noticed a slight drop in oil operating pressures since switching from CJ-4 to CK-4. Another thing he noticed was the coolant temperature running a little higher. Maybe a new generation of coolants will eventually need to accompany new generations of oils.

“Running engines hotter has been an intentional change in recent years to meet emissions regulations. As engines design change, optimizing fluids performance is always on the forefront of our minds,” Glass responds, when asked if that would be needed.

Technically, the use of CK-4 and FA-4 oils instead of the old CJ-4 could also translate into respective fuel savings of up to 1.5% to 2%. But that would be a little optimistic, according to Cummins’ expert. “In general, we have seen a more modest increase in fuel economy between 10W-30 CK-4 and FA-4 oils. However, the actual benefits depend heavily on the engine’s duty cycle,” Glass says.

Still, the benefits should be there, regardless of the specific measurements, says API’s Ferrick.

“There is an old adage that the lighter the viscosity grade of the oil, the better the fuel economy. There is a direct relationship, and this is a long-established principle.”

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