Morphing motor oil
Future engine demands forcing oil makers to retool thinking, approach to the next generation of motor oil

By Paul Abelson, senior technical editor

Motor oil as you know it will soon change.

Until now, new oil classifications were required every time emissions regulations changed, except in 2010. That time the ever more stringent exhaust restrictions were not achieved by changes inside the engine. Rather, the decrease in emissions was achieved by treating the exhaust downstream from the engine with selective catalytic reduction. No changes took place in the engine that further stressed motor oils. That meant truckers could continue to use the CJ-4 classification that the American Petroleum Institute (API) started licensing in October 2006.

When the next proposed classification, PC-11 – short for proposed classification 11 and likely to be designated CK-4 – takes effect in October 2016 to meet yet another round of EPA regulations, CJ-4 will be the first primary service classifications to have lasted a decade. The oil classifications of CI-4, CH-4, CF-2 and CF are still current, but they are not primary.

The new proposed oil is being developed in response to a request by the Engine Manufacturers Association. The group’s members anticipate the changes in technology needed to meet the next round of EPA regulations. Then they work with API to develop tests to ensure that the oils will perform as needed under the newer, more stringent operating conditions.

“The process is very expensive and time consuming,” said Jim McGeehan, global manager of diesel engine technology for Chevron Lubricants. McGeehan is the former chairman of the API committee to develop new proposed categories.

How oil works

The main function of oil is to keep metal from contacting metal. The engine's moving parts have to be kept from contacting each other or they will wear each other down, expand manufacturing tolerances allowed in the production of the engine, and create friction. Friction creates heat that distorts engine parts, further increasing wear and friction. Engine oil provides the film that separates metal parts in motion.

Oil prevents rust and corrosion. It seals gaps between pistons, rings and cylinders to keep combustion gases from blowing into the crankcase. Oil contributes to engine cooling, absorbing heat and carrying it to the oil cooler. It cleans engine parts by carrying detergents and keeps particles from worn metals and combustion byproducts suspended, delivering them to the filter. Oil must be thick enough to function properly when hot, but thin enough to be pumpable when cold.

Issues that prompted the need for a new oil category include:

  • Proposed regulations on both fuel efficiency and greenhouse gas (GHG) emissions;
  • Higher percentages of biodiesel up to and including 20 percent (B20);
  • Concern about engine oil foaming and air entrainment (the creation of tiny air bubbles);
  • Higher projected operating temperatures;
  • Concern about engine oil shear down (the splitting of polymers that are added to thicken oil), which will lead to a reduction in high temperature viscosity.
  • Concern about piston and/or liner adhesive wear, also called scuffing.

The committee, which is now under the chairmanship of Dan Arcy, global OEM technical manager for Shell, meets to evaluate input from refiners and blenders; additive suppliers; and engine makers. The requirements are defined and quantified, and tests are developed and approved to verify that the new oil does what it is supposed to do.

The greenhouse gas and fuel mileage standards that start in 2014 can be achieved with current engine technology.

The thick and thin of it
“The next round of requirements for 2017 will require higher engine temperatures and pressures,” Arcy told Land Line. “We may see some changes in the traditional viscosity we see today.”

Viscosity is a measure of the thickness of the oil as well as its ability to flow under various temperature conditions. Single viscosity oils (designated by only one number on the bottle such as SAE 30 or SAE 40) have their designation based off their flow characteristics at 212 degrees, roughly the operating temperature of diesel engines.

Winter oils, designated with the letter “W” after a number (15W, for example), are thinner oils. They are usually fortified with polymer viscosity improvers. As temperatures rise, the polymers link together to thicken the oil. A 15W-40 oil, with the common viscosity grade in today’s diesel oils, flows at minus 10 degrees and retains thickness of an SAE 40 oil at 212 degrees.

Synthetic oils are made either with highly refined and closely matched mineral oils, or from synthesized uniform oil molecules. Synthetics have better cold flow characteristics and contain no waxes that thicken when cold. They also require less polymer additives.

Thick oils are a drag on engines, reducing fuel mileage. They also make starting harder and increase wear at startup. Thin oils flow quickly on cold starts but may not offer sufficient protection at higher temperatures. Synthetics bridge the gap, offering both cold flow and temperature protection without using as much additive.

“There is no one magic bullet to reach fuel economy targets,” said Arcy. “But switching from 15W-40 to 10W-30 can, by itself, provide a 1.6 percent improvement.”

The 10W-30 oils flow well at minus 20 degrees. Other cold flow oils are 5W, good to minus 30 degrees, and 0W with cold flow well beyond 30 below.

Because of the projected increases in operating temperatures and pressures, Arcy feels there may be a need for two sets of tests for the proposed new classification of oil.

One problem is caused by mechanical shear, the splitting of polymers under operating conditions.

“We may need a new subcategory, a high-temperature test perhaps at 150 degrees Celsius (302 degrees Fahrenheit). Or there may be new property tests for a heavier and a lighter 30 weight,” Arcy said.

Until now, all new categories of oils have been backward compatible – meaning they are safe and effective for use in older engines.

Arcy believes backward compatibility should not be a problem with 15W-40, but there could be two categories of 30 that may not be backward compatible. Some of the new classification oils may be suitable only for 2014 newer engines.

“It is quite possible that 10W-30 will become the most utilized truck engine oil over time, and we may even go to 5W-30,” Arcy said.

The other major concern is scuffing. Metals, even polished surfaces, are not smooth when seen under high magnification. They have peaks and valleys that look like the Alps or the Rockies. As oils get thinner, they have to maintain enough film strength to keep the peaks apart. Otherwise, friction welding occurs. The “welds” join peaks, which then tears the metal apart. The fragments are picked up in the oil and eventually increase the temperature of the oil because of the friction created by the fragments.

“As oils get thinner to improve fuel economy and reduce (greenhouse gases), they will need to have more synthetic content,” Arcy said. “We will need to differentiate higher viscosity oils from lower ones, but there are still too many unknowns to determine what will be required. There is much research yet to be done.”  LL