E&MU: Battle of the Engine Oils
By Stephenie Overman, Contributing Writer, Special to E&MU
This story appears in the May/June 2011 issue of Equipment & Maintenance Update, a supplement to the May 16 print edition of Transport Topics. Click here to subscribe today.
The performance claims of engine oil manufacturers are being put to the test by fleets, engine makers and service centers who study the relative benefits and limitations of conventional, synthetic and semi-synthetic blends.
“We do spend a lot of time looking at oil,” said Russell Thompson, vice president of equipment and shop operations for Swift Transportation. “We have an in-house testing and quality group.” The Phoenix-based carrier uses just under 1 million gallons of oil a year, he said.
Swift conducted a trial study of synthetics on a group of trucks but determined that the pricier blends did not make sense for its needs, said Thompson, who also serves as first vice chairman of the engine study group of the Technology and Maintenance Council of American Trucking Associations.
Swift ranks No. 10 on the Transport Topics Top 100 list of the largest U.S. and Canadian for-hire carriers.
“We wanted to see how far you have to go to make your ROI [return on investment] work,” Thompson said. “We couldn’t see that big a return.”
The company decided to stick with conventional oil.
“Conventional oil continues to get better; the top-tier oils continue to improve,” he said. “The cost-benefit hasn’t been strong enough for us to change over.”
In more severe applications, however, synthetics can deliver results, said Shawn Whitacre, director of materials engineering for engine maker Cummins Inc. For example, he said they stand up well to temperature extremes in both hot and cold climates.
“That’s one attribute [where] synthetic base oils shine,” he said.
One of synthetic oil’s strengths, Whitacre said, is a high viscosity index. Viscosity is a measure of oil’s flow characteristics, or thickness, at certain temperatures. It also is referred to as the motor oil’s weight.
“As oils get hot, they get thinner. As oils get cold they get thicker,” he said. “Ideally, the oil would have the same viscosity regardless of the temperature. You want it to perform as well when you start up the engine as when you’re running in Death Valley.”
Whitacre said he recommends synthetic oils such as 0-W40 when engines are being used in extreme environments. The number before the W indicates how well the oil operates in low temperatures. The lower the number, the more cold it can withstand.
“A fleet of mine in northern Canada that operates in the dead of winter gets a lot of use out of 0-W40,” Whitacre said.
Synthetics also have a high degree of oxidation stability, a measure of how well chemically they stand up to exposure, he said.
Oxidation is more important than it was, say, 10 years ago, because modern engines run hotter, said Greg Shank, manager for structures and materials and also fluids-technology coordinator at Volvo Group North America.
“Reduced oxidation allows us to run the oil at higher temperature for longer periods of time without degradation of the oil,” he said. “Theoretically, it means longer oil life.”
Shank said synthetics have inherently better cold flow and oxidation performance, while semi-synthetics offer less cold flow and oxidation.
He noted that while conventional oils with antioxidant additives are available, the additives drive up the price. However, conventional oils infused with them are still somewhat less expensive than full synthetics, he said.
In between full synthetic and conventional blends are semi-synthetic oils. Created by combining conventional and synthetic blends, semi-synthetics split the difference between the others.
“You get some of the benefits, but it won’t be nearly as expensive” as synthetic, said Brent Calcut, supervisor for chemical technologies for Daimler Trucks North America. “And cost in the heavy-duty engine market is extremely important.”
This issue of return on investment is key for fleets, but producers of synthetic engine oil believe it has advantages that justify the cost. Synthetic oil “helps keep the engine clean through improved sludge, deposit and varnish protection . . . and helps reduce overall engine wear under extreme operating conditions,” Shell Lubricants said in a research brief.
ExxonMobil Lubricants & Specialties did not respond to a request for comment for this article.
Len Badal, commercial sector manager for Chevron Lubricants, described as “myth” the notion that semi-synthetic or synthetic oils provide significant benefits over conventional oils.
Based on Chevron’s research and general information provided by several large heavy-duty engine manufacturers, Badal said the performance benefits of semi-synthetics versus premium formulated heavy-duty engine oils are “marginal at best and typically don’t justify the additional price a customer must pay for them.”
Others, meanwhile, question the limits of how far drain intervals should be extended.
“We still have to stop the truck every 30,000 miles” for maintenance, said Swift’s Thompson. “So, the only thing you’re saving labor-wise was you didn’t have to drain the oil.”
“A truck still needs visual inspection,” added Chris Harrison, who coordinates maintenance for CIT Group Inc., which owns and operates a chain of truck sales and service centers in Illinois. “It needs grease. It needs the filter changed. No matter what
you do, the maintenance facilities still need to put eyes on that truck.”
Cummins’ Whitacre said some fleets find no advantage to extending oil-drain intervals unless a shop visit can be skipped. “If not, you have to take a unit out of service more often, rather than less,” he said.
“When making oil-drain recommendations,” Whitacre said, “we believe that the life of the oil is driven more by the nature of the additive package and by the way the engine is operated, not on whether conventional or synthetic oil is used. They all meet the same pretty demanding specifications.”
The Right Ingredients
Conventional oil is derived from crude oil, while synthetic oil is chemically manufactured, said Shawn Whitacre, director of materials engineering for engine maker Cummins Inc.
Chemical engineers work with “a handful of tools” when formulating oils, he said. The biggest factors in achieving good oil longevity, he said, are “the quality of the base oil and the combination of the additives.” About 80% of engine oil is the base oil; the other 20% is the additive package, he said.
The American Petroleum Institute established five categories of base oil stock to better regulate the performance and formulations of various types of lubricants. Shell Lubricants compiled a list of these five categories:
• Group I is the least-refined base stock. It is most often used in straight-weight, conventional motor oils.
• Group II base stock is refined further than Group I to remove impurities and improve its properties as a lubricant. Group II stock often is used when creating multigrade conventional motor oils.
• Group III base stock is refined to the point that it will perform at the levels of a synthetic base stock and is called a synthetic.
• Group IV base stocks are polyalphaolefin synthetics.
• Group V includes base stocks that do not fit into the other categories, such as esters and polyolesters.
Brent Calcut, supervisor of chemical technologies for Daimler Trucks North America, said that although Group III legally is considered a synthetic, it is in fact an “extremely highly refined mineral oil.” Group IV is the only “true synthetic,” he said, because it is the only type developed “one molecule at a time.”
The additive package, Whitacre said, is a mix of different chemical compounds: detergents, anti-wear agents, dispersants, antioxidants and viscosity modifiers.
“In the end, it becomes a combination of careful scientific experimentation and trial-and-error,” he said.