DPF Cleaning

John Baxter | October 01, 2011

Careful DPF maintenance will boost both your uptime and bottom line.

When the diesel particulate filter was introduced with the change to 2007 engine technology, manufacturers were careful to explain the importance of cleaning the filter to remove engine oil ash that accumulates.

Visible soot is easily dislodged, but going into small passages to clean out soot, especially if it’s gooey or hardened, is much more difficult.

However, because carbon can be sticky stuff, there’s another DPF maintenance concern. A small amount of carbon may adhere tightly to the DPF’s ceramic walls, forming gooey or even hard deposits, especially if the engine is not operating properly. It’s similar to what happens as spark plugs in a car deteriorate and need to be replaced.

Cleaning this stuff out can be far more challenging than getting rid of the relatively powdery ash. Inadequate cleaning can compromise the unit’s life and warranty, while thorough cleaning may result in better fuel economy and more miles before cleaning needs to be repeated.

Due to the DPF’s complicated construction and the tendency of carbon to bond to ceramics, cleaning the DPF is a science. Even cleaning out the ash, which stays fairly loose, is a tedious job because it’s distributed through nearly all the passages.

Because getting a DPF back to 100 percent of its original performance level is so complex, picking the right service provider and ensuring use of the right equipment are critical.

When to clean

The system has a microprocessor that provides warning of troubles or the need for routine maintenance. “The warning lights recognize the miles, fuel used and other factors,” says Detroit Diesel Engine and Component Marketing Manager Brad Williamson. The processor knows the difference between a gradual accumulation of ash and a rapid buildup of soot due to low exhaust temperatures.

In the Cummins Filtration DPF, the diesel oxidation catalyst is on the left, and the particulate filter is at the center. While the catalyst does not need routine maintenance, it can be harmed by engine problems such as head gasket leaks.

Yet most experts believe you shouldn’t wait for a warning light. They advise a more pro-active approach that anticipates the need for cleaning.

“Dashboard warning lights simply indicate when regeneration is required or occurring,” says Paccar Parts Business Development Manager Larry White, “but they are not an indicator of a required DPF cleaning.” In addition to observing the published service interval, other ways to determine it’s time to clean should also be considered: “A driver needs to also pay attention to an increase in the frequency of active regeneration cycles, loss of power, and a decrease in fuel economy,” he says.

Bob Giguere, a product support manager at Inland Power Group of the WheelTime Network, recommends first determining your duty cycle. “Is the truck used for long-haul, regional or local pickup and delivery service?” he says. “Does it idle eight hours a day? Each situation needs to be treated differently. Under ideal conditions, in over-the-road service, you can go 300,000 miles, but with a lot of idling, or local service, you’ll see shorter intervals.” He believes it is often practical to follow manufacturers’ recommended intervals for DPFs operated under favorable conditions.

What’s favorable? Giguere says the amount of oil consumed and engine hours are key factors. A primary reason for clogging is ash from oil the engine consumes, and idling engines use more oil because the piston rings work less effectively. They depend in part on the higher cylinder pressures created under load to work at their best. Idling also means poor combustion of fuel and more soot, potentially fouling the DPF.

Navistar Customer Service Organization rep Mark Ehlers says you should use the interval “published in the operation and maintenance manuals. It’s a best practice to recheck in later manuals, with the dealer, or via the engine maker’s website to see if they have published an update later.”

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