OFF-CAR DPF CLEANING

from April 2023 autotechnician magazine

DPFs – THE BACKGROUND OF ON-CAR TREATMENTS

Off-car DPF cleaning seems like a mysterious art, leading Rob Marshall to visit Carwood in Birmingham to discover what it is all about

Off-car cleaning can reach the areas that on-car cleaning cannot. It is also becoming more popular, as Carwood of Birmingham and LKQ Euro Car Parts attest. Even on an engine that is operating perfectly, all combusted soot leaves a trace of ash behind. This accumulation builds over time but it is not always easy to establish how much ash lies within the filter, compared to soot. As ash cannot be burnt away, frequent active regenerations and high-post regeneration pressure readings are good indications of ash accumulation.

Therefore you cannot deduce by mileage alone how much ash is deposited. A car that is used infrequently could have a higher DPF ash content than one that has covered three times the distance on motorways. Other factors are relevant, too. Service history, low SAPS oil and engine/turbocharger condition are all influencers. The on-board cerium-based catalyst systems that are used mainly on PSA/Stellantis vehicles (and others, such as certain Volvos and Mazdas) deposit the Eolys catalyst as red ash. Contacts within Stellantis told us that refinements over the years have been aimed at reducing the ash load, especially as DPFs have become smaller. Some of these vehicles dose more Eolys into the fuel (increasing the DPF ash loading) if the owner refuels little and often.

You can also consider off-car DPF cleaning in situations, where on-car cleaning is unsuitable. For instance, if the driver has ignored fascia warnings and the DPF has become blocked severely, or if on-car cleaning has either failed, or is impractical. Oil contamination is a further reason why you may consider mail it to them on-car cleaning but be wary that some off-car DPF specialists refuse to clean DPFs affected in this way.

1. Carry out your DPF assessment well in advance. Due to a technical issue, we could not access the pre-clean pressure readings. Therefore, we had to rely on the soot loading figure. Being a calculated value, it is inadvisable to treat it as accurate. For instance, it is possible to see a 300% soot loading accompanied by satisfactory pressure readings.

The guinea pig

As off-car DPF cleaning services tend to be offered on a mailorder basis, many garages are unaware of the process. We are, therefore, grateful to Carwood of Birmingham for showing us its procedure.

The car chosen for this demonstration is a Euro IV DPFequipped 2.0-litre RHR HDI Citroën C5. Despite being elderly, of virtually zero worth and with 136,000 miles recorded, its history has been known from new. Oil changes have been conducted between 6-10,000 miles with the recommended 5W30 C2 midSAPS engine oil and OE quality filters. It has never displayed a DPF problem and was averaging a healthy 524 miles between the last five active regenerations. Its additive tank was refilled 50,000 miles ago with Infineum F7995, the replacement fluid for the OEM Eolys 176. We understand that Eolys Extend is the latest OEM fluid for vehicles of this age – although quality aftermarket suppliers can offer suitable alternatives.

Considering the car's age, mileage and additive specification, we wanted to see what improvements off-car cleaning could bring and how the procedure worked.

Contact Details

Call 0121 552 9524 to arrange collection or drop your DPF off at Carwood in person: Units 2-6 Willow Court, Crystal Drive, Smethwick, Birmingham, B66 1RD.

2. Most off-car DPF cleaning companies will not remove the DPF for you, Carwood being one of them. As many DPFs are not as assessable as the one on this C5, you may have to undertake significant dismantling to access it. Enquire about the turnaround time with your chosen specialist. Excluding time taken for postage, Carwood offers a same-day turnaround on receipt.

3. Remove any pressure pipes and sensors carefully. As they contain a brittle monolith, DPFs are fragile, so package them well. Carwood supplies a packing guide, along with the collection labels. To save time, check the internal brick visually for any cracks; should you find any, advise the customer that a new DPF is needed. Unlike many cars, this DPF can be separated from the oxidisation catalyst.

4. When a DPF arrives with Carwood, its engineers check the unit thoroughly for integrity and damage. This includes using an endoscope to peer inside the DPF outlet and check for issues, such as a melted monolith that would cause a blockage.

5. The picture is from another DPF that has cracked internally. Should damage like this be found, Carwood will inform the garage that the unit is compromised and that cleaning would not solve the problem.

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8. The engineer fits the appropriate adapter to the DPF, so it can be installed accurately. Some DPFs are too long, in which case the exhaust pipe is cut and a jointing pipe must be fitted, upon reassembly to the vehicle. Again, if you think that the DPF is rather lengthy, enquire with your cleaning specialist.

11. Carwood's machine is set to eight pulses per cycle, one every six seconds. The engineer evaluates whether, or not, more cycles are required, or manual intervention is required to obtain the optimum result. The machine warms its cleansing mix to 50ºC.

12. The machine starts, by measuring the DPF's airflow and pressure, which is provided in a print-out (see Step 16). Each high-pressure pulse is spectacular to watch. On this DPF, the video shows the first pulse, where a combination of black soot and red cerium/Eolys deposits are blasted out almost immediately, after the first air pulse. The ensuing bio-enzyme cleansing fluid pulses are as pictured, with relatively a clean soapy solution passing through the filter.

14. Once complete, hot air passes through the filter monolith, drying it out. As moisture creates a pressure increase, the airflow increases and pressure figures drop as the 40 minutes long drying process reaches its conclusion.

16. With the procedure complete, the before-and-after readings can be compared. The airflow has increased from 455 to 468 millibars (a 3% improvement) and the pressure has decreased from 51 millibars to 35 millibars (31% improvement). These figures might not seem impressive but consider that this elderly filter had no recorded faults. Carwood supplies before and after airflow readings on the dispatch note.

17. The engineer then dismounts the DPF from the machine. As the Flash Cleaner machine does not employ very high temperatures, the unit is warm to the touch, not scalding hot. As DPFs that employ Eolys operate at comparatively low temperatures, they are vulnerable to being overheated and so this gentle but strong method suits them well.

18. In case the cleaning process reveals monolith damage that could not be verified before the cleaning process, Carwood's quality control process involves inspecting the DPFs visually again, before they are packaged and returned to the garage.

19. Carwood advises strongly that garages seek and fit the appropriate fitting kits, when installing DPFs. Smearing old gaskets with exhaust sealant risks damaging the DPF severely, should any such material find its way into the monolith.

20. It is easy to forget that the DPF is fragile, so take extra care, when installing it. Carwood advises applying a light smear of high melting-point grease to sensor threads, which lubricates them and helps if any future removal is necessary.

21. Start the engine, check for leaks, and compare the new DPF pressure readings with the old ones. Again, we could not access the real-time pressure readings and so we can rely only on the rather blunt, calculated soot loadings, which cannot differentiate between soot and ash. Even so, the reading has improved by 29%.

22. The car was driven on a post-clean 60 miles motorway trip back to the office. Note that the soot loading calculation has reduced further to 19%. Once returned to base, we performed a live data reading, taken at the pressure differential sensor pipes, showing two-millibar idle speed pressure, which is a good normal figure. Consider, however, that airflow and pressure readings are likely to differ between those recorded by the DPF cleaning company and the live post-testdrive readings.