Maintaining and Servicing Diesel Particulate Filters

August 2011, - Feature

by Tom Berg, Senior Editor, Senior Contributing Editor - Also by this author

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Diesel particulate filters trap soot from the exhaust and ash from motor oil. Most soot is burned off in the course of a truck's operations, but ash stays in the filter's honeycomb substrate and is removed through periodic servicing.

Exhaust in highway trucks is usually hot enough to burn off most soot in a process called "passive regeneration." However, those involved in stop-and-go operations or that idle a lot don't get their exhaust hot enough. The latter must "actively" burn out soot from the substrate by injecting extra fuel just upstream of an oxygen catalyst or by plugging in an electric heater when parked.

Active removal of soot through on-board regeneration can occur one or more times a day, depending on its type of operation, manufacturers say. Often it goes unnoticed by the driver, who may or may not see the indicator light in the instrument panel. But sometimes a warning gets more insistent through the light indicators and the driver must stop and initiate an active regeneration.

Ash from motor oil stays in the filter's substrate and must be periodically blown or washed out. This is done by removing the DPF from the truck and placing it on a special machine. It sends compressed air through the substrate in a series of measured puffs. Detroit Diesel's filters are pressure-washed with de-ionized water, then dried.

Most filters seen by Cleaire Advanced Emissions Controls, which air-cleans DPFs it has previously made and sold, collect about 200 grams (7 ounces) of ash. Some come in with as much as 600 grams (21 ounces).

Blowing or washing out of ash must be done every 50,000 miles or once a year. This, too, is indicated by a warning light. Large fleets have purchased machines to do the cleaning themselves, but most owners take filters or entire trucks to dealers and independent shops for cleaning.

Some owner-operators running out of the Port of Oakland, Calif., have used state money to retrofit their older trucks with DPFs, only to discover they need frequent removal and cleaning. So it's important to ask upfront what the cleaning requirements will be, how long they will take and how much they will cost.

Sometimes an engine produces extra soot or spits out unburned fuel and burned motor oil. These, too, are captured by the DPF, and usually it can't burn them out through normal processes. So occasionally the substrate must be removed from the DPF, then heated and baked in a special machine to burn out the crud. About 10% of filters brought in for servicing need this, manufacturers say.

Cleaning DPFs

Once a mechanic gets at a truck, it usually takes about 60 to 90 minutes to remove the DPF, set it on a machine, clean it for about a half hour, then reinstall the filter on the truck. If baking is required, it may take up to eight hours in the machine. The advantage is that the original DPF stays with the truck, which might add to resale value because its owner can show complete servicing records.

An alternative is the owner removing the DPF and taking it, or a batch of them, to a servicing shop. Here the owner gets back his DPFs, even if he moves them among like-spec'd vehicles in the fleet. This requires him to keep a stock of new or cleaned DPFs to install when loaded up units are removed. An advantage is low downtime for individual vehicles.

Some DPF makers offer an exchange program. Owners send in dirty DPFs and get already cleaned ones to use on their trucks. This reduces the need to stock many DPFs, and the cleaned units are warranted - but the owner doesn't know where they've been. As long as they work well, most owners don't care. A new exchange program by Cleaire charges $450 to $650 to swap a dirty filter for a cleansed one.

Recently, each DPF manufacturer has had to approach CARB for approval of this exchange program. Swapping refers to the movement of the same DPFs among different vehicles within the same common-ownership fleet. Re-designation means the movement of a used DPF from an appropriate engine and application to another, within the same fleet.

Not all manufacturers allow component swapping and/or re-designation. So in some cases, the original filter must remain on the original vehicle in order to stay within CARB compliance.

A manufacturer may deny a warranty claim if swapping or re-designation is performed by a fleet owner, and either the policies approved by the manufacturer are not followed or if the policies are not approved in writing by CARB.

If you have a large fleet and want to look at cleaning your own DPFs, you can purchase machines from several manufacturers, such as Donaldson, FSX and OTC/SPX.

From the August 2011 issue of HDT.


  1. 1. John Webb [ February 03, 2016 @ 07:29AM ]

    I have been told by a so called expert who wanted to sell me a truck without an APU that idling does not clog a DPF because the engine runs very clean at idle. This seems unlikely to me.
    I've also heard that idling is very bad for the DPF because the system isn't running hot enough to burn out the soot and therefore clogs the DPF sooner. Which is true?

  2. 2. Rob [ March 26, 2016 @ 01:39PM ]

    What is true is whether idling or not the dpf will need to be cleaned/serviced at its periodically maintenance schedule. They are easy to clean too.

  3. 3. Eric [ April 08, 2016 @ 06:15AM ]

    Idling is bad for dpf's. If you are running your unit in less than a long haul application, the dpf gets clogged faster. The ideal situation to prolonging a dpf is running your unit on a highway for over a 5 hour period, enabling the truck to run at optimum engine temperatures. Where we see dpf's getting shorter life is , trucks used for farming, garbage truck, busses, construction vehicles and other applications like that.
    When it comes time for cleaning, just blowing it out isn't as effective as a thermal baking. Thermal baking, generally retires efficiency to 97%. Blowing it out, only restores the efficiency of the filter to 75-80% efficiency. Using a liquid cleaning process is a very good method of cleaning also, but it has to be done right. The key part with this process is making sure the dpf is totally dry. If the substrate filler between the core and the outer shell is still wet/damp and then dpf is used the substrate could begin coming apart and damaging the core.

  4. 4. Damon [ July 20, 2016 @ 01:48PM ]

    We service all types of DPF's and we burn out each one, we found that air cleaning was causing our customer base to send them back more often and costing the more $$, with burning each one out they last up to or past the PM miles/hours on the truck or equipment. We also request to go ahead and burn out the DOC, we have found that sometimes it's as dirty or worse the the DPF.

  5. 5. Rick [ August 26, 2016 @ 04:00PM ]

    Urban delivery mostly in town, have to manual regen at least three times a week is this normal for in town driving.

  6. 6. Sarah Smith [ February 14, 2017 @ 01:36PM ]

    My dad had a diesel truck and is worried about his DPF getting dirty. I had no idea that the DPF should be clean out once a year or every 50,000 miles. Another thing to consider is to get your DPF cleaned professionally. That way, you can be sure the job is done correctly and that there will be no problems.

  7. 7. Jonathan Burris [ April 23, 2017 @ 10:38PM ]

    As we have discovered on our Fleet one of the most critical items to "Aftertreatment System " longevity is preventive maintenance. The more we find out as to how a part fails the better steps we can develop to prevent it from happening too early again. We do an annual major set of repairs on our trucks since they are Petroleum transportation units and require an annual vapor tightness test. We have been replacing cranckase filters, cleaning DPF AND DEF dosers to ensure proper delivery of fuel and def to their corresponding systems, changing def filter, checking and cleaning the egr valves- which if are opened will allow spent air into the cylinders essentially cooling down exhaust gases allowing increased soot which will plug up vgt style trubos causing them to malfunction prematurely by sticking. While the def doser is out we inspect for build up and clean accordingly. We also monitor Regen history and pressures if a unit is regening too often or has high pressure we will swap to clean it. We are going to start smoke testing all Intake and exhaust system for leaks. This will allow us to make sure that there is no leaks to have decreased exhaust temperatures and decreased volumetric efficiency of the engine. These practices allow us to go about 120,000-
    150,000 miles between dpf services and at times even more. We have also found out that some of the DPFs we are utilizing have came down in price, which makes swapping out for a new one more efficient in truck down time rather than waiting for it to be cleaned and reinstalling it....


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