The DPF – or soot trap – “filters” harmful diesel exhaust soot particles that should be emptied
regularly (regenerated) to maintain performance and the life of the filter. The DPF needs to be
cleaned regularly, through a process called regeneration (active, passive or forced regeneration).
Regeneration burns off soot at a temperature of 1100 F to leave only a small residue of ash,
effectively renewing or regenerating the filter, making it ready to take on more pollution from the
engine. When a normal regeneration is no longer effective, maintenance will be required.
Why does my DPF get clogged up or full?
Every vehicle type and engine combination can have different reasons why the filter gets clogged.
The rate of particulates generated by the engine, the quality of the fuel, quality of the oil, driving style,
even the location of the DPF in the exhaust system can all contribute to the filter blocking or not
regenerating fully. Things to consider:
- Use a Low Ash Engine Oil – Not using the correct oil specified for your engine can significantly
add to the soot buildup in the DPF.
- Bio Diesel Fuel – Using bio fuels can also contribute to extra soot build up loading in your DPF
as the bio fuel may not burn as “clean” as your regular diesel fuel.
- City driving – Short haul/low speed driving builds up more soot than extended long haul runs.
- Temperature – with exhaust/emission systems, heat is your friend. Regeneration happens at
1100 F, so a lot of short trips, low speed driving will not provide the exhaust system with a high
enough temperature to begin or complete a regeneration, so the filter will plug up faster. Also,
any leaks of exhaust will bring the temperature down and not allow burning soot into smaller
- High Miles – As vehicles with DPF systems age, filter regeneration is harder to complete. Like
any part of a vehicle, they wear out and can no longer be repaired.
Generally, problems arise primarily due to around town stop and start driving where the regeneration
process might not complete. A warning light on the dash will illuminate, or a message indicating the
DPF is full. If you continue to drive in the same manner, the soot build up will increase until other
warning lights illuminate and the vehicle will go into “limp” mode where driving speed is restricted. At
this point, you must get a mechanic involved to do at least a forced regeneration.
Ash is the material that is left when all the carbon on the filter is oxidized to carbon dioxide (CO2).
The primary constituents of Ash in the DPF are:
- Remains of the lubricating oil additive package
- Engine wear metals
- Fuel contains almost no ash
- Most fine particulate matter is filtered out of the fuel before it gets through the fuel system
- Fuel contains almost no dissolved constituents that are not carbon based
- Ash will remain permanently in the filter until cleaned
- Over time, this ash build-up reduces the soot handling capability of the filter and requires more
frequent regenerations to maintain exhaust flow and fuel economy.
- Most manufacturers recommend cleaning ash at a regular fixed interval.
- Some fleets have begun to clean DPF filters as part of a regular Preventive Maintenance
activity (i.e. every 120,000 miles). Cummins new 2017 L9 engine series recommends
maintenance every 200,000 miles for the DPF and DEF filter.
What do I do if my DPF warning light is on
Follow vehicle manufacturer’s handbook on procedure to unblock the DPF. It should be possible to
start a complete regeneration and clear the warning light simply by driving for 20-40 minutes or so at
speeds greater than 50 miles an hour.
If you ignore the light and keep driving in a relatively slow, stop/start pattern, soot loading will continue
to occur until around 75% filter capacity. Then you can expect to see other dashboard warning lights
illuminate too. At this point driving at speed alone will not clear the blockage and the vehicle must go
to a mechanic for a forced regeneration. If regenerations start to occur frequently, this is a sign of a
problem and/or an old full DPF.
DPF Cleaning or Replacement Intervals:
- DPF’s are designed to run for 200,000 to 500,000 miles or more without cleaning as long as
conditions are IDEAL:
- Ultra Low Sulfur Diesel is used (ULSD)
- CJ-4 Low Ash Oil is Used
- High Speed driving that regularly generates On-Truck Passive Regeneration Activity
- Properly Working Turbo and EGR Systems
- If any of the above conditions are not satisfied, DPF’s will require cleaning or replacement
much earlier than 200,000 miles.
- OEM Replacement filters can cost over $5,000. This makes cleaning or exchanging of the
DPF the best option for most operators.
- Prices charged for DPF Cleaning range between $350 and $500, depending on location and
cleaning method used.
- Some manufacturers offer exchange programs in lieu of cleaning, which usually run between
$600 and $800.
The DPF cleaning service for Class 4-8 trucks is in the 50,000- 215,000 miles. Frequency depends
upon the duty cycle.
Options for cleaning my DPF, beyond regenerations
The three major options for cleaning DPF’s beyond the forced regenerations are:
- Cleaners that help a forced regeneration
- Removing the DPF and use air burst machines that blow particles out of the filter
- Removing the DPF and cooking the Soot into Ash and blowing it out.
The options above are in order of lowest risk to highest risk to the DPF and also in order of cost of the
maintenance procedure. Any time you have to remove the DPF from its assembly, being a ceramic
material, it can be damaged or broken.
There are various cleaners on the market that purport to:
- Increase the temperature of regeneration through Fuel Additives
- Decrease the temperature required to convert the soot to ash through a catalyst
- “Soften” the soot so a regeneration will be affective
Flamingo sells and recommends LiquiMoly’s DPF cleaner that is a combination of 2 & 3 above. The
process takes less than one hour. You do not need to remove the DPF. The process involves
spraying into the DPF assembly through a removed sensor port when the assembly is not hot with a
water based fluid. The fluid should be allowed to soak for 20 minutes. This softens up the hard soot
particles allowing them to regenerate to ash on the next regeneration. A follow up spray then follows
the first spray process to protect the coating on the DPF. Next a forced regeneration. We also sell a
fuel additive that can be used to increase the temperature of regeneration.
DPF Air Bursts
If normal maintenance with regeneration or cleaners with regeneration are no longer effective, then
the next step could be removing the DPF from its housing and using a mechanical means to remove
the soot and ash.
- First thing, Pressure test and identify if DPF if damaged/cracked or too plugged for proper
cleaning without a high temp bake (regeneration at 2,200F).
- Various mechanical processes involve high or low pressure air bursts and/or employing
centrifugal forces to move particles out of the DPF.
By far the most effective cleaning method is cooking the DPF at 1,200 to 2,200 F. This is very
effective at converting all the soot to smaller ash. This process usually includes DPF Air Bursts
before or after.
- Again, first thing, Pressure test and identify if the DPF is damaged/cracked
- Cook the DPF. This may take a day to do.
- Pressure test and/or weigh the DPF to assure that the DPF is in compliance to OEM Specs
- If out of compliance a new DPF will need to be purchased.
- The DPF generally can be cooked up to 3 times during its useful life. The DPF has a coating
and over time this coating brakes down and the DPF starts to crumble.
Best Practices for Maintenance
- Drive the vehicle on the highway with speeds over 50 mph for over 45 minutes, regularly.
- Check that the exhaust gaskets are sealing as designed which holds in heat for the DPF.
- Every other maintenance interval, have your mechanic clean the DPF with LiquiMoly
- DPF Cleaners (LM5169 + LM5171) https://www.youtube.com/watch?v=020MdntTw34
- Cost runs less than $30 per truck for the LiquiMoly products.
- Requires Equipment: Wand / pressurized Sprays / and possible wand extension.
- LiquiMoly Disel Purge (LMCF1-DP) Less than $6. Removes deposits on engine injectors and in the combustion chamber for improved performance of engine. Better
Engine performance will keep the emmissions systems running as designed.
- At every maintenance interval, have your mechanic force a regeneration of the DPF.
- If regenerations are happening more and more, and the LiquiMoly DPF cleaner is not cleaning
as it initially did, consider removing the DPF and mechanically cleaning or cooking it.
- Be active in your maintenance of the vehicle. Other problems like poor engine performance
and EGR problems will quickly clog the DPF.