New oil choices: Thick or thin

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.”