For years, some fleets have turned to synthetic engine oils for easier starts in cold-weather climates and to help them extend oil drain intervals.
Today, the business case for synthetic oils goes beyond that, as synthetics and synthetic blends help oil makers deliver lower-viscosity oils that help improve fuel economy and stand up to the higher pressures and temperatures of today's engines.
You've probably heard about the growing use and acceptance of lower-viscosity engine oils, down to 10W-30 and even 5W-30. Several engine makers in Europe are now factory filling with 5W oils, and North American engine makers are getting comfortable with 10W-30.
Daimler, for one, has given the nod to some synthetic products, provided they meet the OE's standards, but cautions they aren't the exclusive ticket to extended oil drains.
"Synthetic oils may be used in Detroit engines provided they are approved by a Power Guard Oil Specification," explains Brad Williamson, manager of engine and component marketing for Daimler Trucks North America. However, he says, "the use of synthetic oils does not necessarily ensure the extension of the recommended oil drain intervals beyond the limit."
Oils and fuel economy
Lower-viscosity engine oils can improve fuel economy by reducing internal friction and the resulting parasitic losses. And oil makers often turn to synthetics or semi-synthetics to help design lower-viscosity oils that still offer the protection needed in today's diesel engines.
"Low-viscosity oils such as 10W-30, 5W-30 and 5W-40 can provide several benefits, including improved fuel economy from 1% to 3% on the average," says Mark Betner, heavy-duty lubricants manager for Citgo.
For instance, Shell says its RotellaT5 10W-30 synthetic blend gives fuel economy benefits of up to 1.6% in on-the-road field testing in medium-duty trucks compared to traditional 15W-40 oil. And earlier this year, Chevron released Delo 400 LE Synthetic 5W-30, which it says can deliver up to 4.5% fuel economy improvement.
While petroleum-based oils are still very much in the game, tougher greenhouse-gas-reduction and fuel economy targets due in 2018 could solidify the case for synthetics, or at least semi-synthetics.
Engine makers have asked the American Petroleum Institute to develop a new diesel engine oil classification that will help them meet those greenhouse gas/fuel economy standards. The category is currently referred to as PC-11, for proposed category 11.
In addition to moving toward lower viscosity ratings, the new oil category will demand that these oils maintain that viscosity under certain high-temperature, high-stress conditions.
"The new category of NAFTA engine oils that will be released for 2016 will have a lower viscosity category component," Williamson says. "This will likely increase the trend of synthetic oils on the market. However, synthetic oils will not be necessary."
To balance the demands of the new category with fleet demands for affordable oils, you may see oil makers turn to semi-synthetic oils.
"Semi-synthetics are made up of base oils, performance additives, viscosity improvers," explains Dan Arcy, global OEM technical manager for Shell Global Solutions. "A portion of the base oil is synthetic, blended with mineral oil. You won't get all the performance benefits of full synthetic, but it costs less."
Extended drains and more
The problem with synthetic engine oils is the cost. It's hard to justify draining $20-a-gallon oil at roughly the same intervals as $8-a-gallon mineral oil. In both cases, it's not the base stock that wears out; usually it's the soot load in the oil or change in the TBN (total base number, a measure of the oil's ability to neutralize acid) and the breakdown of various additives that prompts an oil change.
Synthetic oils are often touted for their ability to help fleets extend oil drain intervals, which helps improve the business case. However, pushing out oil drain intervals isn't something to do lightly. To get the full benefit of the exercise, you need the full support and cooperation of your engine maker, your oil provider and the filter providers.
PAM Transport of Tontitown, Ark., under the supervision of Carl Tapp, now retired and offering maintenance consulting, managed to pull off an astounding 150,000-mile drain interval with the help of full synthetic oil prior to the advent of diesel particulate filters. After that, he scaled back to 100,000 miles using semi-synthetic. Although there's not enough room here to tell the whole story, the results are worth mentioning, because they illustrate what's possible.
Will it work for everyone? Absolutely not.
Drain intervals are very, very fleet- and application-specific, Tapp says.
"Soot is a combustion byproduct, so a fleet that burns less fuel, i.e., has better fuel economy, could get away with longer drain intervals than a fleet with poor fuel economy," he points out.
An engine at idle creates more soot than an engine at rated power, so fleets with high idle time will have more soot in the oil. Some engines just have a higher propensity for creating soot. Engines with larger sumps can hold more soot in suspension because the percentage of soot is relative to the volume of oil. There are many other factors, such as winter or summer fuel, eastern or western fuel, ambient humidity, engine load factor, etc.
Mack's Director of Powertrain Sales, Dave McKenna, calls the PAM test interesting, but emphasizes that you can't simply take that data and spread it around other applications.
"This is rocket science," he says. "Extending drain intervals is very complex. You can't say just because they did it, I can do it too. The value proposition for synthetics might not be there for everyone in improved performance, but in certain applications, you could get away | with extending drains if you're careful."
Because lower-viscosity oils provide less oil resistance at start up, the engine turns over more readily. That's why some fleets operating in extremely cold climates use low-viscosity synthetic and semi-synthetic oils. Even in milder climates, the easier starts improve battery and starter life, says Citgo's Betner. That's what Tapp found in his experience at PAM. "You need a certain rpm at the flywheel to get the engine to fire," Tapp says. "When it's cold and your oil is thick and your batteries are marginal, you might not get the 80 to 90 rpm you need."
Several factors are at play here, he says. All post-2010 engines are running much tighter internal tolerances than previous engines, making them harder to crank. High-pressure common rail fuel injection adds even more load to the starter.
In addition, because of the need for some deep cycling to support hotel loads on the truck, he says, the cranking capacity of the dual-purpose cycling/starting batteries in common usage today is slightly compromised - enough to create problems when trying to start in the cold.
Tapp's experience shows that a 5W-30 oil compared to a 15W-40 oil improved the startability of the engine considerably.
"That was a minus 20 degrees Celsius cold temperature test, but in even milder weather with marginal or weak batteries, the oil viscosity makes a difference," he says.
Today, everything is on the table when it comes to fuel economy.
"The days of engine makers getting a 1.5% to 2% gain in fuel economy with a single design change is probably behind us," McKenna says. "Now, we're bundling a lot of small changes together to get maybe 1% to 1.5%. Oil is going to be part of that."
To get there, Tapp says, "We have to reformulate the oil spec. Eventually, the only thing that will make sense is syn thetic oil. I don't think conventional mineral oil will ever get down to those specs. Forget the dollar amount; I don't think you'll have a choice."
Synthetic lubes shine in driveline applications
Wouldn't it be grand to go 500,000 miles between engine oil drain intervals? If not for the heat, soot and other combustion byproducts present in the engine crankcase, that might be possible. In transmissions and differentials, where combustion usually isn't an issue, synthetic lubes will last half a million miles.
"Synthetic base oils last longer in a vehicle's drivetrain because they do not degrade as rapidly as classic petroleum base oils," says Bruce McGlone, senior chemist, materials engineering at Meritor. "Lower temperatures in gear boxes allow a synthetic lubricant's [heat-activated] EP additives to last longer before they are depleted, so they can go longer between changes."
They also withstand extreme stresses, temperatures and friction better than non-synthetic alternatives, says Mangesh Ingle, service solutions manager for Eaton Vehicle Group.
"They contain special high-pressure and anti-wear additives that protect and clean metal parts and cope better under the intense, gear-face pressures present in transmissions and differentials," he explains.
Most driveline factory fills use synthetic oils. When certain approved lubricants are used, extended warranties are sometimes offered.The operative word here is "approved," which generally refers to a certain OE or SAE J2360 performance specification.
"Lubricants that do not meet the Dana specifications also may have a negative impact in component performance," says Steve Slesinski, director of global product planning for commercial vehicle products at Dana Holding Corp. "This occurs primarily in the areas of seal performance, gear wear and bearing wear, all of which can lead to gear noise, or worst case, gear and axle failures."
Of course, synthetic oils are more expensive. "It is cheaper to remove crude oil from the ground and refine it than it is to make oil molecules via synthetic chemistry," explains McGlone. However, when you look at that longer drain interval, the cost per mile of synthetic oils is often less than petroleum-based oils.
To get the most from your synthetic lube investment, Meritor recommends the following best practices.
- Monitor the correct oil level in axles and wheel ends. Reduced levels of oils will reduce hardware life and performance.
- Use the correct and hardware-approved multi-viscosity oils in axles and wheel ends.
- When possible, use axles equipped with magnets in the housing, as well as the small drain plug.This reduces wear dramatically.
- Use off-the-shelf additives in the axle oil.These additives will almost always interfere with protection provided by at least one of the oil's additive packages.
- Drown the hardware. If the axle and/or wheel ends have been covered in water during use, change the lubricant as soon as possible.
- Exceed the hardware manufacturers' limits on contamination. Used-oil analysis is a minor expense that can save big money.
From the December issue of HDT.