PC-11 will become the first API HDDEO spec to include an engine test from outside the United States, the Daimler DD-13. Its also possible that PC-11 will extend a Noack volatility minimum requirement of 13 percent by weight to the SAE 10W-30 grade. This 13 percent limit was previously introduced for all viscosity grades except10W-30 when CJ-4 was adopted and has been part of European standards for many years.

A bigger change is that the 10W-30 grade in PC-11 will be split into oils that are safe to use in engines built before the initial model year for this specification (scheduled to be 2016) and those that are not. The backward compatible subcategory will have a higher minimum limit for high temperature/high shear viscosity, 3.5 millipascal seconds. The non-backward compatible subcategory goes all out for fuel economy and will have a lower HTHS minimum of 2.9 m Pa.s. As a result, the fuel economy version could see some increased use of higher quality Group III oils to get the required balance of lower base oil viscosity and adequate volatility control.

For engines operating at largely steady temperatures, such as on-highway trucks, HTHS is probably the principal determinant of lubricant-derived fuel economy. It mainly determines the hydrodynamic viscous resistance in the engines large main bearings and piston skirts – one of the main lube energy loss mechanisms. Since the additive package contributes significantly to overall viscosity in low-viscosity lubricants that have high additive treat rates, such as 10W-30 HDDEOs, its the base oil viscosity that will be squeezed for fuel economy. But lighter base oil blends will need good Noack scores.

In the U.S., 10W-30 is the largest volume light multigrade for trucks. However, this grade is unlikely anytime soon to replace 15W-40 as the favored grade for owner-operated trucks. The 13 percent Noack requirement has for a while been achievable in 15W-40 oils with Group II base oils, mainly because of the higher base oil viscosity of this lubricant.

For PC-11, it seems the improved volatility requirement is not just for the sake of controlling oil thickening and, hence, fuel economy. It is also aimed at minimizing base oil derived deposits on diesel particulate filters and improving compatibility with after-treatment systems such as selective catalytic reduction. Again, this could push the base oil blend toward a small proportion of light Group III even for the market leading 15W-40 grade.

The Truck and Engine Manufacturers has requested that PC-11 provide improvements in oxidation stability, aeration control and compatibility with biodiesel blends, as well as shear stability and scuffing/adhesive wear. At least the first three of these can be improved by base oils choice. Antioxidant response generally improves with higher paraffinic content in the base oil, which correlates with higher viscosity index. Aeration generally improves with lower aromatics content, which could reduce Group I content in diluent oils for additive packages and viscosity modifier concentrates – the sole remaining use of Group I base oils in recent category crankcase lubes. Compatibility with biodiesel blends is aided with lower solvency base oils, again another nail in the coffin of Group I, even for diluent oils.

GF-6 is a fuel-efficient passenger car category. While the fuel economy engine test gets a minor update, fuel economy improvement comes mainly from introduction of a new SAE viscosity grade, SAE 16, under GF-6B designation. This follows on the successful introduction of SAE 0W-20 for passenger car motor oil fuel economy oils in GF-5. The historic SAE multi-grades will fall within GF-6A.

XW-16 grades will have a lower HTHS minimum of 2.3 m.Pa.s and will require very good quality Group III base oils to be thin enough to meet HTHS requirements and yet be nonvolatile enough to meet Noack requirements. It will be interesting to see if this grade requires any special diluent oils such as Group III for viscosity modifier concentrates.

If GF-6 is to have genuine fuel economy retention capability, it does beg the question of whether the Noack cap can remain at 15 percent by weight. Ive not seen any indication that it will be brought into line with the proposed 13 percent maximum for PC-11 oils, despite the fact that there will inevitably be wider use of high quality Group III oils in GF-6 grades for other reasons. Hence, they could meet a lower Noack limit. Evaporation of light ends from the base oil is just as likely to cause problems meeting fuel economy retention requirements as oxidative thickening of the lube.

So to return to the question posed at the beginning, will PC-11 and GF-6 put new demands on base oils? The balance of higher quality Group III versus Group II may well shift. Will they require an out-and-out new base oil? I dont think so.