How Not to Hate Your Diesel Particulate Filter
This cutaway reveals the insides of a diesel particulate filter and shows how the small tubes through which the exhaust passes could get clogged with soot.
Photo by Les Smart.
We all know by now that the mandated 2007 and 2010 emissions standard rules radically changed on-highway diesel-powered trucks and tractors. To reduce emissions to satisfy the Environmental Protection Agency-mandated level of soot and NOx, engines needed to add technology to meet the new standards.
As a result, the infamous diesel particulate filter (DPF) came into being in 2007, and diesel exhaust fluid (DEF) was introduced in 2010 into the exhaust stream to reduce particulates and NOx. While this change was a benefit to the environment, the introduction of both brought tales of woe from truck owners regarding the added expense, maintenance, and failures.
The DPF’s Job
The sole intention of the DPF is to catch and retain particulates, or “soot” in layman’s language. The DPF requires periodic soot removal cycles, termed “regeneration” or “regen” for short. These regens burn the accumulated soot out of the DPF at extremely high temperatures. Most of these “passive” regens occur almost unnoticed at highway speeds.
While the filter burns off soot at speed, soot will accumulate during idling or slow traffic. Trucks that don’t accumulate a lot of mileage, those in extended idle periods such as stop-and-go duty cycles in urban environments, or stationary power take off (PTO) applications may require the driver to commence an active, or manual regen.
Regens are generally accomplished by activating a switch on the dash of the truck. An active regen takes approximately 20 minutes, depending upon how clogged the DPF is. When a regen is commenced manually, the vehicle should be parked and away from buildings, brush, people, and animals.
This should be the only maintenance necessary on the DPF system in the first 100,000 to 150,000 driving miles. However, if high idling occurs regularly during the duty cycle, regens will be more frequent.
Teach your drivers to pull over in a safe place and park if a manual regen is required. Hopefully, your duty cycles will have the truck doing automatic regens all or most of the time.
Keep it Clean
According to Dan Whittle, service manager for Cumberland Trucks, an international dealer serving Tennessee with its headquarters in Nashville, the following issues will cause premature clogging of the DPF filter:
- City driving with a light load
- Stop-and-go traffic
- Excessive use of engine brakes
- Inappropriate engine oil type: engines using non-low ash oil meeting the API performance classification CI-4/SL will retain soot and ash prematurely
- Operator error
With operator error, there are many issues to consider. Failing to run an active regen when the truck asks for it, or interfering with the truck in any way that does not allow it to complete an active regen, will cause problems. Drivers need to know the difference between the exhaust temperature light and the DPF light. If the driver never sees the DPF light come on, that’s a good thing. This means the truck is doing what it is supposed to do. Whittle says drivers bring their trucks in for service because the DPF light never comes on.You’ll know when the truck needs a manual regen because the regen light will come on.
Do it — don’t bypass this, even temporarily. If your truck is equipped with a gauge in addition to a light, the gauge will progress from green to orange to red. Do not increase engine load after the regen light comes on, Whittle says.
Manual regens should be run when the gauge is orange. By the time your gauge is in the red, you will be experiencing a power derating of the engine.
This FSX Pneumatic Cleaning Machine is used by dealers to clean DPFs. The thermal cleaner on the far left is connected to the dust collector, which is connected to the pneumatic cleaner. The air flow test bench sits on the far right. The DPF must be removed from the truck to use this system.
Photo courtesy of FSX Equipment.
A Job for Professionals
There are plenty of truck components that can be serviced DIY — but a DPF is not one of them. Using shop air to blow off soot or ash will not clean the filter. Restoring a DPF to its optimal performance level is a science; specialized equipment is needed.
In terms of how often to service, it is essential to observe your truck’s published service interval. Severe duty cycles may increase the frequency of active regenerations, which is a good warning to service the DPF sooner than the published interval.
Regarding where to service, the best course of action is to follow the truck manufacturer’s recommendation. Most truck dealers clean DPFs, though truck service centers and diesel emission service specialists also offer this service.
Trucks can be brought in for servicing or the filter can be removed and brought in by itself. Other services offer pickup and delivery. Some DPF makers offer an exchange program in which dirty DPFs can be swapped for remanufactured clean ones. Consult your specific manufacturer first, as some manufacturers forbid component swapping, which will cause denial of a warranty claim.
If you are looking into a third-party service to clean your filter, ask the provider if it warranties the cleaning and make sure to understand the details of the warranty. Some third parties work with franchised dealers. If so, call one of those dealers for a recommendation.
In general, exercise extreme caution if you’re thinking of having your DPF serviced by a third party. Going through your manufacturer’s franchised dealer, which typically charges about $200 to $500, is the safest way to ensure you won’t face any warranty issues if a faulty DPF causes damage to other components.
While that cost seems high, this cleaning can greatly extend the life of the component while reducing maintenance downtime and costs. This cost is relatively inexpensive when compared to the total cost of the vehicle when purchased. The DPF cleaning can also be combined with other scheduled service work to further minimize downtime.
During a dealer cleaning, a baseline reading is taken of the restriction of airflow through the filter using the air flow test bench. Most OEM filters have a baseline of what is considered acceptable air flow. If needed, the filter will be baked in a controlled cycle to burn any soot and convert it to ash.
Once the DPF has gone through the cleaning process, its air flow is tested to ensure that it meets the manufacturer’s specs for a cleaned DPF. The DPF is then remounted on the truck.
This process could take up to 90 minutes, though baking the filter could take up to eight hours.
When to Clean
This exhaust pipe comes from a brand new medium-duty truck that had just undergone a 2,000-plus mile trip to the up-fitter from the factory, with most of the journey at highway speeds. You can see by the discoloration of the metal the high temperatures that were generated in only 2,000 miles with auto regens at highway speeds. DPFs are delicate instruments — you can’t use some elbow grease and a shop vac to clean them.
Photo by Les Smart.
Trucks that make frequent stops combined with heavy-duty cycles will need their DPFs cleaned around 100,000 miles. Trucks with less severe duty cycles may wait until 150,000 to 200,000 miles. The specific use of your trucks will dictate when cleanings are necessary.
Replacement of the DPF is much costlier than cleaning one. A new filter will cost more than $2,000; a used one can be had for $1,200 to $1,600.
So, what’s the $64,000 answer as to how long my DPF will last in my service? I have seen Class 6 and Class 7 trucks with 6- or 7-liter engines regularly go up to 150,000 miles or more before needing to clean the DPF. Their ultimate life could be in the range of 250,000 miles.
Class 8 trucks with 12- to 15-liter engines should attain 250,000 miles and could go as long as 400,000 to 500,000 miles. The hours and mileage will vary, of course, depending upon your duty cycle. Using good, clean, low-ash diesel is a key to longevity.
Learn to appreciate having DPFs on your trucks. We all deserve to have cleaner air to breathe — especially our children and our grandchildren.