NASHVILLE, Tenn. — Reducing maintenance costs related to exhaust aftertreatment systems requires fleets to develop their own preventive maintenance (PM) schedules and not rely solely on OEM recommendations.
That’s the advice from Bryan Stewart, director of maintenance with Jones Logistics, who was part of a panel dubbed A Deep Dive Into Emissions Aftertreatment System Maintenance held at the spring meeting of the American Trucking Associations’ Technology & Maintenance Council. The fleet he oversees consists of 164 tractors out of Columbia, Miss.
“It seemed our trucks were behind a wrecker as much as they were on the highway delivering product,” Stewart lamented. “We decided we needed to look internally at our PM process. We started defining a checklist and adding new components. Once we had the checklist in place, we defined processes to ensure the same work out of each technician each and every time.”
The result was a four-page PM checklist that took 3.5 hours to complete. Some changes implemented by the company included a “no driver fill” policy for coolant, so the maintenance department could better track whether coolant was leaking and causing issues for the aftertreatment system.
“We needed technicians to know how much coolant we used,” Stewart said, “so we implemented a coolant management system.”
Other components, not directly related to the aftertreatment system, were also more closely monitored. A stronger focus was placed on battery cleanliness and the fleet moved to absorbent glass mat (AGM) batteries because of their higher current and deeper cycles. Terminals were kept clean, as were grounds and cables, with extra attention given to any terminal that touches an aluminum component, which is more susceptible to corrosion.
Jones Logistics purchased video scopes for the inspection of diesel exhaust fluid (DEF) tanks and had technicians regularly check the debris screens. A refractometer was used to evaluate the quality of the DEF itself.
“We started having the technician inspect the doser valve,” Stewart said. “We found instances where the valve had become loose and got salt buildup around it.”
Exhaust components, including gaskets, clamps, and bellows, were all inspected. A ceramic-type bellow was adopted to address issues in which fiberglass material was escaping.
Diesel particulate filter (DPF) housings were another source of concern, with components coming loose because of insecure clamps that were overlooked. So DPF housings were added to the checklist.
“The amount of heat a DPF puts out would cause zip ties used to secure wiring harnesses to become brittle,” Stewart observed.
The fleet implemented an oil analysis program to determine how often DPF cleanings would be required, rather than relying on the OEM recommendations. Stewart paid especially close attention to total base number (TBN) figures and used falling TBN numbers as an indicator a DPF needed cleaning.
“We wanted our TBN to be no less than 3.5,” Stewart explained. “We set our DPF service interval based on TBN values.”
Generally, that baseline saw DPFs being pulled at 250,000 miles or 5,000 hours of service. The company chose to stock extra DPFs so it could have its own filters cleaned rather than swapping filters through an exchange program.
“I didn’t want to worry I was picking up someone else’s problem,” Stewart reasoned.
DEF filters are swapped out every 100,000 miles and drivers were educated to watch for contaminants entering the DEF tank.
“We had numerous failures because a driver allowed contamination,” Stewart said. “We’re constantly preaching about cleanliness when filling the system.”
Air filters also received some extra attention, which Stewart said is one of the most overlooked items in fleet maintenance.
“It filters 18,000 gallons of air per gallon of diesel fuel (consumed),” Stewart said. “We opted to change air filters every service. We measured a 3/10ths of a mpg increase in fuel economy.”
That improvement netted an annual savings of US$1,656.38 per truck, he added.
“We have to change our mindset and look more at predictive maintenance than preventive maintenance,” Stewart urged. “Use the data you have available to determine what your fleet needs.”
Tom Chase, director of maintenance at 200-truck fleet Bellavance Trucking, agreed with the need for customized service intervals.
“Every PM we monitor aftertreatment codes. Don’t only look at the active codes, look at the inactive codes too,” he suggested. “Let the computer talk to you and tell you a story. Our average DPF (cleaning interval) is 250,000 miles between changes. Use the OEM number as a guideline.”
This is especially important as OEMs continue to push out DPF cleaning interval recommendations to as much as 600,000 miles.
Keeping it clean
Mark Collins, director of maintenance and engineering with UPS, shared a way his fleet reduced its DPF problems by adding a wet wash to the cleaning process. In February 2016, UPS had a 46% DPF fallout rate. Contributing to this were cracked substrates (50%), damaged housings (25%), melted substrates (13%), contaminates (7%), and flow issues (5%). By October 2016, the fallout rate actually increased to 51%, leading UPS to take action.
Collins said the company moved to a single-source provider of DPF cleaning to bring more consistency to the operation. It was using the bake-and-blast cleaning technique in which the filter is baked at high temperatures and then the ash is blown from the filter.
The company decided to test a wet wash system on filters that couldn’t pass the bake-and-blast process and noticed some improvements.
“It removes softened ash with no damage to the cells and cleans each cell individually,” Collins explained, noting it’s especially effective at improving flow.
UPS chose to combine the two cleaning methods and now runs all DPFs through the bake-and-blast cleaning process before putting them in the wet wash.
“We have seen an additional half pound of ash removed by using the wet wash process,” Collins said.
By January 2017, UPS saw its DPF fallout rate decrease to 37%.