New oil choices: Thick or thin

Nov. 11, 2013
Viscosity may determine which oil—or oils—fleets will stock

Complications are never a good thing in trucking, especially when they involve routine maintenance tasks such as changing engine oil.  That’s one of the reasons lubricant makers struggled mightily over the years to craft engine oil blends that not only met strict chemical limits related to exhaust aftertreatment technology, but also to make them backward compatible so they could be used in new and old engines alike.

Going forward with Proposed Category 11 (PC-11) oils, however, that won’t necessarily be the case.  There’s not one but two new blends being created in the category to meet federal greenhouse gas (GHG) rules for heavy trucks being phased in between model years 2014 and 2018.

“Unfortunately, this trend is a sign of the times,” explains Mike Wyant, technical services manager for Universal Lubricants.  “It’s very possible that an end user will need to carry multiple engine oils to cover the requirements.  We’ve seen that occur in automatic transmission fluids and other lubricants.”

The GHG rules jointly announced by the Environmental Protection Agency and the Dept. of Transportation back in 2010 cover three distinct sets of trucks, each with their own compliance timeline.

For tractor-trailers, those engine and vehicle standards begin with the 2014 model year and establish a 20% reduction in carbon dioxide (CO2) emissions and fuel consumption by the 2018 model year.  The rules for heavy-duty pickup trucks and vans call for separate gasoline and diesel truck standards to be phased in starting with the 2014 model year.  These standards would be expected to achieve up to a 10% reduction for gasoline vehicles and 15% reduction for diesel vehicles by the 2018 model year (12% and 17%, respectively, if accounting for air conditioning leakage).  Finally, the standards for vocational vehicles would kick in for the 2014 model year and are targeted to meet up to a 10% reduction in fuel consumption and CO2 emissions by the 2018 model year.

Performance metrics

Meeting such fuel economy mandates necessitated change across numerous truck components, systems, and materials, especially engine oils, notes Dan Arcy, OEM technical manager for Shell Lubricants.  “The PC-11 performance category is being developed with targeted improvements in several performance areas,” he explains.

Such changes include:
  • High-temperature oxidation control, as some engines will be running up to 18 deg. F hotter.
  • Protection from adhesive wear, as a move to low viscosity or “thinner” oils requires good protection against wear and metal-to-metal contact.
  • Improved aeration control, as it will boost the ability of engine oil to release air that can get trapped within it. This requirement may necessitate the replacement of current aeration testing procedures.
  • Boosted shear stability, as the mechanical shear of polymers used in current oil can result in the loss of viscosity, meaning the oil becomes too thin.  That may also require changes to current shear stability tests.

In addition, the new PC-11 designation will feature two “subcategories,” says Arcy, with one featuring oil viscosities much like what exists today and the other formulated with lower (thinner) oil viscosity geared to provide improved fuel economy and reduced CO2 emissions.

“At this time, I cannot comment on the new components or chemical that may be used in PC-11 engine oils,” Arcy stresses.  “But if you look at the performance improvements targeted for PC-11 oil, we will need new or additional oxidation inhibitors, new or improved anti-wear components, and a different mix of base oils, to name a few of the changes.”

All of that may impact the backward compatibility of the new PC-11 oils, especially the lower viscosity grades, he says.

“We will need to look at PC-11 a little differently since we are looking at two subcategories,” Arcy explains.  “The heavier viscosity grades are targeted at being fully backward compatible.  For example, a PC-11 SAE 15W-40 will be able to be used in applications that call for a CJ-4 performance SAE 15W-40.  In addition, the PC-11 SAE 15W-40 will provide the additional benefits listed above.”

Yet the second subcategory, or lower viscosity, PC-11 oil may not be backward compatible, he warns.  “These thinner oils may not provide the protection in older equipment,” Arcy explains.  “At this time, the engine manufacturers have not provided details on which of the older engines may or may not allow the use of PC-11 low-viscosity oil.”

Not backward

Still, Arcy believes it may be a little too early to tell whether a one-oil-fits-all engine oil strategy is definitely a thing of the past.  “This really will be determined by what happens with the backward compatibility issue,” he says.  “It may be that for a period of time, a year or two, a fleet may have to carry two different oils, one for legacy engines and one for the new lower CO2, more fuel-efficient engines.  More information on this will be forthcoming.”

Universal’s Mike Wyant thinks it’s unlikely the new low viscosity PC-11 oils will be backward compatible.  “PC-11 will be unprecedented,” he says.  “The new category will be the first of its kind to establish two new subcategories, initially being identified as PC-11A and PC-11B.  The PC-11A will be a traditional robust subcategory with typical viscosity grades like a 15W-40, 5W-40, and 10W-30.  But the PC-11B will be more of a ‘fuel economy’ version, with lower viscosities and lower high temperature/high shear (HTHS) values.  The viscosity grades will drop down to 10W-30, 5W-30, and perhaps even lower.”

In short, “the PC-11B subcategory will not be backward compatible as the viscometrics and base oil combinations will be too light to sufficiently protect former engines,”  explains Wyant.

Mark Nyholm, technical product manager for Amsoil, points out that the reason the PC-11B formula most likely won’t or can’t be backward compatible is because gaining better fuel economy is the main research goal.
“It is industry known that lowering the HTHS number can improve fuel economy; however, it can also reduce wear protection,” he says.  “Some engines [from the] past were not designed to operate on lower HTHS and viscosity numbers.  Additionally, older engines still on the road [using] lower viscosity oils may not get the proper wear protection they need for continued service.  That or their oil consumption may increase significantly, resulting in cost increases from additional oil as well as increased emissions out the exhaust pipe from burnt [engine] oil.”

According to Len Badal, commercial sector manager for Chevron Products Co.,  a fleet may have to stock two engine oils if it decides to use high temp/high shear products to gain higher potential fuel economy performance.

“In a case like this, the fleet may only be able to use the new oils in newer engines and with ones that the OEMs are comfortable with recommending these lower HTHS products in their engines,” he explains.  “If a fleet also operates older engines, then the fleet may have to use a second oil with normal HTHS to protect those engines and ensure they perform appropriately.”

Natural gas

Universal’s Wyant adds, though, that the adoption of truck fuels such as natural gas complicates the development of future engine oils to a degree as well—and may force the need to use multiple engine oils. 
“Testing will be required in not only conventional diesel fuel but in alternative fuels as well,” he says.  “Always consult the owner’s manual when determining what engine oils to use when faced with alternative fuels.”
Wyant points out that natural gas engine oils, in particular, occupy an unusual spot as they are somewhat of a hybrid between diesel fuel and gasoline oils.  “They are formulated differently to handle the different issues associated with the combustion of natural gas,” he explains.

Chevron’s Badal thinks most alternative fueled engines—even in the natural gas space—should be able to use the new PC-11 formulation, though important caveats remain.

“PC-11 oils will be able to handle all the fuel types that fleets may opt to run, from biodiesel blends (assuming a maximum 80/20 mix of petroleum-based diesel and biodiesel) to dimethyl ester,” he says.  “Fleets should not worry about utilizing these fuels with their diesel engines, assuming they use premium PC-11 diesel engine oils for lubrication.”

Badal emphasizes that it is a little more complicated with   natural gas,  since it depends on the type of engine technology being deployed.  “If a spark-ignited CNG (compressed natural gas) engine is being used, then an approved CNG oil should be utilized to prevent spark plug fouling, valve guttering, and ash buildup on the piston crowns,” he explains, as such deposits “are detrimental to CNG engines and can cause early potential engine failure.”

But Badal points out that if the truck engine has been adapted for dual-fuel engines running on both liquefied natural gas (LNG) and diesel or just pure LNG, then a fleet may be able to use PC-11 oils  depending on engine configuration.

“If a fleet has a mix of diesel and CNG engines, the fleet will most likely have to stock two oils to provide optimum performance,” he says.  “But if the fleet has a combination of diesel and pure LNG or diesel/LNG dual-fuel engines, then it may be able to use one oil—PC-11—for both.”

Amsoil’s Nyholm explains that one reason for the differences between pure diesel and natural gas engine oils is the difference in the by-products of combustion and the additive package components, such as detergents and dispersants.

“For example, diesel oils have chemistry to combat the negative effects of soot, a by-product of combustion, in the engine oil,” he notes.  “By contrast, natural gas engines do not have these same chemistries, as soot is not a by-product of natural gas combustion.”

Understanding the different by-products of combustion also requires lubricant manufacturers to study their interaction in the engine’s oil sump and modify the additive packages to protect the engine from wear and corrosion.  “Different fuels burn at different temperatures, exposing the lubricant to varying temperatures,” Nyholm adds.  “Oxidation resistance is an important aspect to controlling viscosity creep over time due to high and higher engine temperatures.”

Still, Nyholm believes that the concept of a maintenance facility stocking a couple of different engine oil products won’t be too outside the norm, as this process is already in play today among diesel-only engines.
“With the rapid advancements of technology, engine OEMs are further specifying lubrication requirements, making it increasingly difficult to satisfy all of them with one product,” he says.  “And it’s likely to get worse before it gets better.”

Lubricant makers confess the real struggle will be to get the end user to accept the lighter-weight, low-viscosity oils themselves.

“While there is certainly a noticeable trend of lighter viscosity engine oils entering the marketplace, there is still an adherence to heavier weight engine oils,” says Universal’s Wyant.  “There are end users convinced that lighter weight engine oils won’t perform adequately for engine protection [thus] there will tend be that stigma of the lighter weight oils not meeting the needs of the engine.”

That view is echoed by Amsoil’s Nyholm.  “As long as there is the belief that my application is more severe than yours, SAE 40 viscosities will not go away,” he says.  “There are people today who still do not budge away from the old 15W-40.”

Shell’s Arcy points out, however, that there’s been increasing use of lighter viscosity oils such as SAE 10W-30 grades simply because they offer improved fuel efficiency and pumpability versus SAE 15W-40 blends. “Most of the Class 8 truck/engine manufacturers either factory-fill with SAE 10W-30 or offer it as an option for factory-fill,” he adds.  “And most of the Class 8 truck/engine manufacturers allow SAE 10W-30 as an option or primary recommendation for service-fill.”

Over time, Arcy expects to see an increase in the use of light viscosity oil and a decline of the heavier viscosity oils. “Fleets are always looking for ways to reduce their operating cost and/or maximize operating efficiencies of their fleet,” he explains.  “There will continue to be movement in the direction of products, operating condition, etc., that can help improve fuel economy, driving a reduction in operating cost.  Improved efficiency by optimizing maintenance intervals and improving uptime will continue to help improve the bottom line.”

Looking to the future, Arcy says there will be a continued push towards lower viscosity, synthetic or semi-synthetic lubricants that will provide improved fuel economy benefits and help reduce CO2 emissions.
“Those issues are big in the engine oil industry,” adds Universal’s Wyant.  “End users desire longer drain intervals and better fuel economy.  Thus, future categories will continue to optimize and further improve engine oil quality in those directions.” 

About the Author

Sean Kilcarr | Editor in Chief

Sean previously reported and commented on trends affecting the many different strata of the trucking industry. Also be sure to visit Sean's blog Trucks at Work where he offers analysis on a variety of different topics inside the trucking industry.

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