by Sean Kilcarr, FleetOwner.com

Lubricant makers are aiming to develop new testing procedures for proposed category 11 or “PC-11” engine oil to account for the potential benefits as well as risks posed by switching to new lower viscosity formulations.

At the recent 2014 Technology & Maintenance Council (TMC) annual meeting in Nashville, TN, Lilo Hurtado, applications engineer at ExxonMobil, moderated a technical session that reviewed the impact of switching from the typical 15W-40 engine oils used in today’s diesel truck engines to lower viscosity 10W-30 and 5W-30 blends; blends expected to characterize at least one of the possibly two PC-11 formulations being tested.

“At the end of the day we need to be mindful of the 2017 and proposed post-2018 greenhouse gas (GHG) federal regulations that aim to conserve fuel consumption by heavy trucks,” Hurtado explained. “Lower viscosity oils are going to help us deliver on that.”

John Loop, technical manager for Lubrizol, noted that as of right now, CJ-4 is the blend dominating the 1.4 million metric tons of global heavy duty engine oil (HDE)) market representing 67% of all diesel truck engine oil blends sold followed by CI-4 at 25%.

Yet many of those CJ-4 oils are low viscosity blends, he stressed with some OEMs factory-filling their truck engines with such blends – noted Daimler Trucks North America, which has factory-filled its Detroit branded engines with 5W-30 oils since 2006.

When you talk about liquids, Loop added, “viscosity” really relates to the degree with which fluid resists flow under an applied force. Thus lighter-weight oil requires less energy to pump within the engine cylinders, meaning engines don’t work as hard and thus consume less fuel.

In comparing 10W-30 and 5W-30 blends to their 15W-40 brethren, Loop said the lower viscosity oils helped boost fuel efficiency in Class 6 truck operations by 3% to 6%, depending on application, with Class 8 trucks seeing a 1% to 2% fuel economy gain, again dependent upon application.

Yet Greg Shank, executive staff engineer for Volvo Powertrain, stressed that fuel economy can’t come at the expense of other critical needs being demanded of PC-11 oils, specifically: maintaining engine durability, biodiesel compatibility, maintaining current oil drain intervals, and the trickiest of the bunch, backward compatibility.

He added that PC-11 tests are going to begin in the second quarter this year as the deadline for the introduction of an official PC-11 formulation is April of 2016.

Shank noted the critical test metric is what’s known as “high shear/high temperature” or HTHS and the lower the HTHS number the better the oil will be in delivering fuel efficiency improvements.

As a result, PC-11 is expected to be split into two formulations: a “carryover” blend dubbed PC-11-A with a 3.5 HTHS rating and a fuel efficient PC-11-B blend with a 2.9 to 3.2 HTHS rating.

He added that PC-11 testing expected to cost between $2.5 million and $3.5 million, with the cost split three ways, between the American Chemical Council (ACC), the American Petroleum Institute (API), while the Engine Manufacturers Assn. (EMA) and Truck Manufacturers Assn. (TMA) splitting the last third between them.

Where the lower viscosity PC-11-B blend is concerned, Jeremy Dean – DTNA’s supervisor of chemical technology – said tests need to be developed to examine the potential issue of what’s called “liner scuffing,” where oil does not adhere properly to the cylinder and piston head lining, thus leading to cracks and oil leaks.

“There’s been no scuffing issue with CJ-4 oils but then we did not conduct adhesive wear tests with it,” Dean explained. “That’s why we’re developing an engine scuffing test for the new oils.”

That’s one reason why additive packages for new PC-11 oils will need to be “optimized” in order to prevent scuffing while also boosting fuel economy, said Dan Nyman, technical advisor for chemical technology at engine maker Cummins.

He explained that without engine oil optimizers, the fuel economy gains from lower viscosity PC-11 oils would only range from 0.75% to 1%, while gains would increase to between 1% and 3% with optimized additive packages.

ExxonMobil’s Hurtado closed out the discussion with several cautionary notes for fleets as the new PC-11 oils get readied for introduction: first, to be very careful if considering using such oils in older model engines and to be very clear when ordering them from lubricant suppliers as their labeling could potentially be very similar to the lower viscosity oils used in gasoline engines.

“Be very specific to order oils with lower viscosity for diesel engines as the same nomenclature is used for low viscosity oils developed for gasoline-powered car engines,” he said.