The basic rule of lubrication says, if the engine starts, the oil must flow for the entire life of the oil in the engine, regardless of engine type, SAE viscosity grade or temperature, she said. Failure to follow this simple rule can result in catastrophic engine failure.

Oliver identified three major trends in the lubricants arena, and described the importance of viscosity modifier selection in formulating oils in light of those trends. The three key trends, she said, are higher performance and longer drain lubricants; increasing use of hydroprocessed Group III base stocks; and growth of biodiesel fuels.

Formulating for Longer Drains
Oil life monitors and consumer awareness are slowly driving oil drain intervals up in North America, said Oliver, where passenger car drain intervals have climbed from about 4,000 miles to 6,000 miles in the last decade. Recommended drain intervals of most of the premium European passenger car engine oils have double in the last 10 to 15 years, and are two to three times longer than those in North America, she added.

Lubes are subject to numerous stresses in the engine, and extended drain intervals further exacerbate these conditions, Oliver continued. To clarify the impact of viscosity modifier choice on low temperature performance in aged oils, Infineum formulated two premium SAE 5W-40 oils, differing only in VM type, and aged the oils in vehicles on a rolling road chassis dynamometer. The test vehicles were placed in a cold chamber, and oil pressure sensors were placed in various parts of the engine.

The two viscosity modifiers were dubbed VM A, an amorphous viscosity modifier which is completely soluble in base stock over a wide range of temperatures, Oliver told Lube Report; and VM B, a high ethylene olefin co-polymer viscosity modifier which has crystalline segments that may be prone to interaction with waxes in the base stock, impacting low temperature pumpability. The premium VM A and conventional VM B are both widely available commercially, Oliver said.

The oil formulated with VM A reached critical engine parts within a few seconds of startup, even after 10,000 miles in service, said Oliver. But the oil with VM B, after just 8,000 miles of service, was unable to develop any pressure, even three minutes after startup, starving the engine of lubrication. The VM B oil formed a non-flowing, gelatinous mass at low temperatures, she said.

Formulating for Group III
Group III base stocks, often considered key to meeting the high performance standards of top-tier lubricants, may respond differently to additives, depending on their individual processing or composition, Oliver said.

Wide use of modern base oil processing technologies is resulting in significantly higher levels of branched wax in the base stocks, she said. Additive technologies with inherently low sensitivity to waxes are highly advantaged in formulating with these base stocks.

Infineum tested base oil sensitivity in aged SAE 5W-40 oils formulated with six different Group III base stocks, to measure the performance of VM A and VM B with each base stock. (The fresh oils all showed satisfactory fluidity.) Risk of lubrication failure, as measured by the yield stress in the MRV TP-1 test, said Oliver, was severe with VM B in four of the six oils. Risk of failure was nil in all the aged oils with VM A.

Formulating for Biodiesel
Biodiesel use is growing, Oliver said, and one key problem for lubricant formulators is biodiesels tendency to accumulate in a crankcase, because of its significantly lower volatility than conventional diesel fuel.

Infineum developed an engine test cycle to simulate biodiesel dilution of the crankcase lubricant in service, and showed that while dilution is minimal in high temperature highway driving cycles, it reaches 1 to 5 percent in low temperature city driving cycles. The researchers then looked at the impact on low temperature pumpability of fresh 5W-40 oils, formulated with VM A or VM B, diluted with different biodiesels.

The results, said Oliver, showed that the oil with VM A showed no risk of failure in dilutions of rapeseed or soy-based biodiesels, and only low risk with palm-oil-based fuels. On the other hand, the oils with VM B showed low to medium risk of failure in the rapeseed and soy-based dilutions, and medium to severe risk with palm oil.

Properties of an oil can change dramatically with aging, and extended drains and biodiesel contamination can stress the oil even further, Oliver concluded. Formulation choices are key to sustained performance, and must be compatible and consistent with trends in fuel, base stock and performance requirements.