Diesel particulate filters appeared in 2007 model-year trucks. After nearly 10 years we are still grappling with maintenance issues.

Diesel particulate filters appeared in 2007 model-year trucks. After nearly 10 years we are still grappling with maintenance issues.

Aftertreatment system maintenance is proving to be more costly than tire maintenance, making it possibly the single most expensive maintenance item on today’s trucks. Parts costs are prohibitive, the associated downtime can be crippling, and much confusion still exists about the care of these systems even after eight years in the field.

“When they were first deployed, they were supposed to be a hands-off, self-maintaining component that would look after itself behind the scenes with some simple cleaning procedure required sometime in the future,” says Scott Perry, Ryder Fleet Management Solution’s vice president of supply management. “We’ve learned since then that’s not always the case.”

Perry says while overall understanding of the systems is improving, Ryder has customers who are just now taking delivery of their first aftertreatment-equipped trucks. Fleets with extended trade cycles and those that put off buying such equipment for as long as possible are now at the front end of that learning curve. They will benefit greatly from early adopters’ hard-learned lessons, but it will be some time yet before the industry is comfortable with and confident about maintaining these things.  

One fellow with a bird’s-eye of the confusion is Darry Stuart. He calls himself an independent “limited-time executive” who provides maintenance and operational expertise for dozens of fleets, and he’s a frequent moderator at the American Trucking Associations’ Technology & Maintenance Council’s Fleet Talk and Fleet Forum sessions. The tire cost comparison is his, and he says fleets need to take a more predictive approach to aftertreatment system maintenance.  

“We’re just now beginning to accept that we have to do things differently from what we have been doing all our lives in order to maintain the aftertreatment system,” Stuart says.

At the Shop Talk session at this year’s TMC general meeting in Nashville, he asked the crowd if anyone is doing anything differently at PM time about aftertreatment system maintenance. Nobody put up their hand.

“What I got out of that was that very few people accept the fact that they have to change and do more preventive aftertreatment system maintenance,” he says.

While Stuart agrees some aftertreatment systems have issues of their own, he maintains much of the trouble fleets have with them are caused by upstream failures.

“The delicacy of the aftertreatment system can be disrupted by many things,” he says. “Any upstream failures, many of which you may not even be aware of, can have disastrous consequences. For example, something as simple as a leaking exhaust manifold gasket cannot be tolerated today. We can’t let those things go anymore. They can cause heat loss that affects the passive regen performance.”   

The list of upstream failures can include but isn’t limited to:

  • leaky injectors
  • excessive idling
  • leaky exhaust pipes, manifold gaskets
  • coolant leaks
  • EGR (exhaust gas recirculation) cooler leaks
  • the so-called 7th injector (doser valve)
  • turbo failures
  • sensors and wiring harness failures

Fleets have spent years streamlining their preventive maintenance processes to be as efficient as possible, but Stuart says being proactive on aftertreatment systems may mean the 2.5-hour PM is a thing of the past. Among other things, diesel particulate filters are subject to a lot of vibration and possible impact damage, so canisters should be inspected regularly for possible damage, cracking and breakage. Stuart also suggests inspecting and cleaning the sensors and their exposed contacts to ensure they have good electrical connections and they are not gummed up by contaminants that could cause false fault codes.

Stuart also has been pushing his fleets to do forced regeneration during PM services. It may add an extra hour of labor, but considering the possible cost of not taking that extra step, it’s a bargain, he says.

“Drivers are always up against hours of service, and taking an hour at roadside to do a parked regen doesn’t work for them,” he says. “They will push the truck as far as they can to avoid that unpaid hour. Some push it too far and then we have a very expensive service call to deal with. Considering the towing cost, the cleaning cost and the downtime, never mind the drivers’ lost wages and how unhappy they will be, an hour in the yard doing a forced regen at PM time looks pretty good. We have to start thinking that way to stay ahead of these things.”

A clean DPF, following the air and thermal cleaning process.

A clean DPF, following the air and thermal cleaning process.

Not one size fits all 

The greatest challenge in establishing a predictive maintenance routine for aftertreatment systems is that no two trucks are the same. Even when there are no additional mechanical problems affecting the system, the condition of the diesel particulate filter is highly duty-cycle dependent.

“Long-haul trucks running consistently high exhaust temperatures may never need a parked regen,” Perry says. “On the other hand, a stop-and-go duty cycle, or applications with a high percentage of idle time, such as concrete mixers, will result in a situation where the aftertreatment system cannot maintain itself. In those instances, forcing parked regens on a consistent basis could be beneficial.”

Perry says the industry remembers the hard-target 300,000- to 400,000-mile cleaning intervals suggested by the OEMs in the early days. Since then, however, some have learned that cleaning may be required sooner and more frequently, depending on the duty cycle as well as possible oil contamination that can cause sulfated ash to build up in the DPF.

“Getting more frequent requests for parked regens probably means the DPF needs to be cleaned,” he says.

Performing regular checks of the oil and coolant levels is highly recommended. If any of these are found chronically low or there are signs of contamination, there is a high risk of face-plugging the diesel oxidation catalyst, which will increase backpressure, says Mario Sanchez-Lara, Cummins’ director of on-highway marketing communications.

“After an ineffective active or even passive regen, the system monitors will trigger fault codes and activate a dash lamp to recommend inspection,” he says. “Ignoring those warnings will trigger the engine protection system to derate or to limit vehicle speed.”

While all OE systems will perform similar functions, sometimes the warning, fault codes or dash indications will be different. That can get confusing in a mixed fleet like Ryder’s.

With thousands of vehicles in different age groups, in different applications and different brands of chassis, engine and aftertreatment systems, Perry has kept up with the performance indicators and now has a pretty good idea of when certain trucks need attention.

“We look at the history of the vehicle and its applications and we apply a service recommendation based on mileage, fuel consumed and hours in service,” he explains. “The data we’re getting from the newer vehicles is improving and they are able to give us a better indication of the soot load, etc. There’s more insight and visibility there now. But the older vehicles still require planning and scheduling of a cleaning cycle as opposed to the system telling you when a cleaning is due. And I fully expect that will improve with the coming generations of vehicles.”

Oil contamination builds up on the inlet side of the DPF.

Oil contamination builds up on the inlet side of the DPF.

Repair and replace

Repair costs have escalated since EGR and DPFs first appeared. Randy Obermeyer, terminal manager of Indiana-based Batesville Logistics, says his exhaust system maintenance and repair costs jumped from about $400 per year per truck in pre-EGR days to over $2,400 post-DPF and pre-selective catalytic reduction (he hasn’t yet nailed down a number for that addition to the system.) In other words, he’s spending 290% more today than a decade ago. A poor-performing DPF will also allow fouling of the downstream NOx catalyst, which is itself a pretty expensive piece to replace. 

“In the past we would let small things on the engine slide, like minor oil or coolant consumption, charge-air cooler or exhaust manifold leaks,” Obermeyer says. “You can’t do that today. Practically everything that can fail out in front of the aftertreatment system will harm the DPF, and those minor problems become a major expense.”

A dirty DPF undergoes cleaning in an FSX cleaning machine

A dirty DPF undergoes cleaning in an FSX cleaning machine

Kurt Swihart, Kenworth marketing director, notes that “oil and/or coolant consumption all play a factor with DPF contamination and will result in the engine controller commanding more frequent regenerations due to the excessive backpressure created by the oil/coolant contamination. Drivers should monitor oil and coolant usage and notify their maintenance department immediately if usage increases.”

In previous engine generations, oil and coolant leaks were obvious because of the smoky exhaust. That’s all trapped in the DPF now, so monitoring oil and coolant usage (and using the correct oil formulation) is critical now.

“If [oil or coolant] levels are dropping with no external signs of leakage, you have to know it’s going somewhere,” notes John Moore, product marketing manager, powertrain at Volvo Trucks North America. “Check fuel filters for blackening that may result from crankcase oil mixing with fuel from a leaking injector. Check the fuel tanks for blackening of fuel, which indicates a mixing with crankcase oil.”

Doug Gunter, director of warranty at Peterbilt, cites several ways to minimize DPF-related downtime and maximize the life of the aftertreatment components:

  • Follow the recommended maintenance schedule for the vehicle, including the aftertreatment system.
  • Use quality diesel exhaust fluid. Not only is there an indicator light for low DEF, but also if the DEF quality is detected to be below acceptable levels.
  • Reduce idle time to save fuel and extend DPF service intervals.
  • Do not disable the regeneration process. “This will create a buildup of soot that could eventually cause the engine to derate and can reduce the life of components.”

Black oil deposits line the exhaust manifold. All this material winds up in the DPF and turns to ash.

Black oil deposits line the exhaust manifold. All this material winds up in the DPF and turns to ash.

Heat is your friend

Even some traditional parts are no longer any good to you, like off-the-shelf spiral-wound exhaust tubing. Proper DPF performance requires that exhaust systems be leak-free from the engine through the treatment system, and that as much heat as possible is retained by the piping.

“In the past, the engine outlet and the treatment system were commonly joined using a strip-wound metal hose,” says Scott Swank, vice president of engineering at Tru-Flex LLC, which makes exhaust products. “However, after new EPA standards were enforced, the nominal leakage rate and lack of thermal insulation associated with the original metal hose approach made it obsolete. Bellows formed from a solid steel tube were found to be the most suitable replacement.”

Cummins recommends placing the aftertreatment as close as possible to the engine and using double wall exhaust piping or insulation wrap to retain heat.

“An aftertreatment architecture that has less surface area exposed to elements will retain heat and reach temperature ranges needed for passive or active regeneration more easily,” says Sanchez-Lara.

And here’s a final word to the wise for used truck buyers. The vehicle’s first owner probably spec’d and maintained the

vehicle to run to the trade-out point and no farther. Chances are they tried to avoid a second DPF cleaning or replacement interval, and may have even ignored problems with the system in its final weeks or months of service. When buying used, you can almost count on have to put money into the aftertreatment system. It might be better to get it addressed up front, roll that cost into the price of the vehicle and build it into the payments, than to shell out anywhere from $5,000 to $20,000 in the first weeks or months of ownership due to an unpredicted failure.

“Diesel particulate filters have become an interesting part of the maintenance puzzle,” says Stuart. “They have been around since 2007 and they aren’t going away. They are getting better but we still have a lot to learn about them.” 

About the author
Jim Park

Jim Park

Equipment Editor

A truck driver and owner-operator for 20 years before becoming a trucking journalist, Jim Park maintains his commercial driver’s license and brings a real-world perspective to Test Drives, as well as to features about equipment spec’ing and trends, maintenance and drivers. His On the Spot videos bring a new dimension to his trucking reporting. And he's the primary host of the HDT Talks Trucking videocast/podcast.

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