Handling the heat and gunk left over from combustion is an engine oil’s biggest challenge. The introduction of the lower emission standards means oil’s job has gotten even tougher. With a 40 percent drop in NOx (the diesel pollutant that’s arguably hardest to control) and a 90 percent drop in particulate required under the Environmental Protection Agency’s 2007 regulations, engine oil has significantly more heat and soot to deal with than ever before.
Most engine makers are using water-cooled exhaust gas recirculation technology, familiar to operators of 2002 engines, to control NOx. In the new engines, though, EGR will recirculate as much as twice the exhaust as in 2002 models. The diesel particulate filter will pull particulates out of the exhaust stream.
Feeding all that exhaust back into the air intake at about 300 degrees Fahrenheit creates two challenges. The first is an increase in heat, both between the piston and cylinder liner, and underneath the piston, where the oil cools the piston.
The second is more soot. Increased exhaust in the combustion chamber reduces the oxygen concentration, making it difficult to burn diesel without a lot of soot forming in the process. Soot must be kept in suspension or the oil could thicken into sludge, causing reduced lubrication.
Beyond the stresses from increased EGR, the DPF presents additional challenges for oil. The DPF continually burns off the soot it collects, while also trapping ash, which eventually must be cleaned from the DPF. The ash comes mostly from oil additives that end up in the DPF due to normal oil consumption.
To extend the time between DPF cleanings, oil developers reduced the amount of ash in the oil by adding less detergent and total base number additives. These additives combat acidity in the oil, and keep deposits from forming. Oil providers also had to guarantee reduced oil consumption via better refining. Fortunately, the ultra-low-sulfur diesel fuel required for use with 2007 engines not only helps reduce particulates, it significantly lowers acidity as the acids in the oil derive mostly from fuel sulfur.
To help the new engines meet these challenges, oil producers developed the CJ-4 formulation. CJ-4’s benefits “include a decrease in oil consumption, reduced piston deposits, better viscosity control and better oxidation stability,” says Steve Goodier, director of CJ-4 technology for BP Castrol.
With the new oil, “rings and lands stay cleaner, which reduces oil consumption, meaning more time to build ash in the DPF,” says Dan Arcy, technical marketing manager for Shell Lubricants. And that means longer intervals between DPF cleanings.
While CI-4 still will be available until about 2010 because of market demands, and CJ-4 can be as much as 15 percent more expensive than the earlier formulation, oil company experts urge consideration of CJ-4, even for those continuing to run pre-2007 vehicles. It’s the “most robust” category ever defined by the American Petroleum Institute, says Jim McGeehan, Chevron global manager of diesel engine oil technology. “The oils have to pass nine fired-engine tests and six bench tests. Five of those tests are run on the earlier, 500 ppm low sulfur fuel.”
The Caterpillar C13 ACERT test, for example, runs for 500 hours at full power and then measures piston deposits and oil consumption. The Cummins ISB test looks at valve train wear, injector screw wear and lifter life. It runs the oil at 6.5 percent soot levels and then inspects parts such as the rocker cover for sludge.
“I would prefer CJ-4 even in a 2004 truck,” Citgo’s Betner says. “CJ-4 is better, even with the earlier higher sulfur fuel, and more so with ULSD.”
Shell found wear rates dropped by 38 percent with CJ-4, Arcy says. The company is so confident about the performance of CJ-4 that it began offering it exclusively in the packaged oil market in October, though CI-4 Plus will still be available to bulk buyers, Arcy says.
Using CJ-4 in combination with an older engine and exclusive use of the new fuel could greatly extend oil change intervals because much less acid is likely to form in an engine’s crankcase. However, experts recommend tracking any interval beyond the manufacturer’s recommendation with an aggressive oil analysis program.
As to running older oil with a new engine, there is some agreement that using CI-4 won’t damage the DPF, but will only make it necessary to clean it more frequently. Check with the engine maker to make sure using CI-4 won’t compromise any of the engine systems or void your customer’s warranty.
For More Information:
ExxonMobil Lubricants and Specialties
www.exxonmobil.com
(800) 443-9966
Chevron
www.chevronlubricants.com
(952) 842-1000
Shell Oil Co.
www.shell.com
(713) 241-6161
ConocoPhillips
www.conocophillips.com
(281) 293-1000
76 Lubricants
(800) 435-7761
BP Castrol
www.bp.com
(877) 582-3727
Citgo
www.citgo.com
(800) 248-4684
