A great deal has been written about Diesel Particulate Filters and about DPF additives. Sadly, not all the information ‘out there’ is entirely accurate. On this page we hope to dispel some of the more common myths and misconceptions that exist in the field of DPF additives.
Click on a misconception below to reveal the truth about DPF additives.
“Any Diesel Fuel System Cleaner Will Do”
Fuel additives for a wide range of applications have been available for many years. As ‘DPF Cleaners’ are often more expensive than the other fuel additive options sold alongside, it is sometimes suggested by sceptics that ‘DPF Cleaner’ additives are no different in content. It is therefore suggested that a generic ‘Diesel Fuel System Cleaner’ will do the job just as well. This belief often comes hand-in-hand with the claim that ‘DPF Cleaners can’t work because they cannot survive combustion.’
In fact, any credible fuel additive for DPF treatment will include a Fuel Borne Catalyst. FBCs are different from traditional fuel additive components in that they survive combustion in their active form. This allows them to perform their soot-clearing function in the exhaust system and DPF. The organic chemicals used in traditional Diesel Fuel System Cleaners will not be effective in the exhaust as they are destroyed in the combustion chamber. The higher price tag of most credible DPF Cleaners is also down to the higher cost of FBC chemistry relative to traditional fuel additive components.
“How Can Any Additive Survive Combustion?”
Fuel additives for a wide range of applications have been available for many years. Most claim their effectiveness in cleaning the fuel system up to the point of the engine, or else through altering the characteristics of combustion to give increased power or reduced smoke. As ‘DPF Cleaners’ are often sold alongside these other fuel additive options, it is sometimes suggested by sceptics that ‘DPF Cleaner’ additives are no different in content. And it is therefore suggested that ‘DPF Cleaners can’t work because they cannot survive combustion.’
In fact, any credible fuel additive for DPF treatment will include a Fuel Borne Catalyst (FBC). FBCs are different from traditional fuel additive components in that they survive combustion in their active form. This allows them to perform their soot-clearing function in the exhaust system and DPF. The organic chemicals used in traditional Fuel System Cleaners will not be effective in the exhaust as they are destroyed in the combustion chamber.
“Why Not Just Take The DPF Off?”
Drivers frustrated with regular DPF problems may be tempted to remove the filter entirely. This is encouraged by the many firms advertising DPF removal or ‘DPF Delete’ services quite openly on the web. They sometimes claim that it is not illegal to remove the DPF, and that the vehicle will still pass MOT smoke opacity tests without it. These are however, half-truths.
Although it may not be illegal for companies to carry out DPF removal work, the vehicle owner is left in a somewhat unfortunate position. This is because the vehicle is rendered illegal to drive on public roads (although it may be acceptable to use niche situations such as track racing). The law states that it is an offence under the Road Vehicles (Construction & Use) Regulations (Regulation 61a (3)) to use a vehicle which has been modified in such a way that it no longer complies with the air pollutant emissions standards that it was designed to meet. DPF removal will almost inevitably result in this requirement being broken. The Department for Transport has issued guidance clarifying this.
Emissions tests carried out as part of a standard MOT are not currently sensitive enough to show whether a DPF is fitted. It is therefore irrelevant that a smoke opacity test may be passed without one; DPFs are designed to produce much cleaner exhaust emissions than that. However, since February 2014, a visual check of the exhaust system has been required as part of the MOT test and if a DPF should be fitted but is found missing, this will result in automatic failure.
“Ash vs. Soot”
Carbon-based soot, formed by incomplete combustion of fuel, is not the only thing which collects in DPFs. Metal-based impurities caused by burning small amounts of engine oil forms ‘ash’ which builds up slowly builds up over time in the DPF. Unlike soot, this ash cannot be burned away through regeneration.
Eventually (after 100,000+ miles) ash will build up to the point that the DPF needs clearing out, necessitating an external filter clean, or replacing. This lifetime may be reduced, however, if there is a problem with the oil system, or the wrong type of oil is used (see DPF Problems – Possible Causes).
It is sometimes claimed that DPF Additives, containing FBCs, should not be used as they will contribute to the ash and lead to the DPF blocking up anyway. To a certain extent, this is true, as the metal oxide from the FBC is deposited in the DPF. However, use of DPF Additives at normal dose rates (as recommended by the supplier) generally contributes only a small amount to the ash in comparison to the normal build up due to the oil.
“With Active Regeneration There’s No Need For An Additive”
The possibility of the DPF becoming over-loaded with soot is something vehicle manufacturers are aware of. One of the methods commonly used to avoid DPF blocking is ‘Active Regeneration’. This involves kick-starting DPF Regeneration by squirting fuel directly onto the DPF (either on the exhaust stroke of the engine or through a dedicated fuel injector fitted in the exhaust system). The extra diesel effectively acts as ‘lighter fluid’ to ignite the trapped soot and burn it away. The system runs automatically when the vehicle ECU detects soot build up in the DPF.
Some people with such a system may think they would have no need of a DPF cleaning additive. After all, the vehicle sorts itself out. However, if the DPF has to actively regenerate very regularly – for example in slow speed urban driving – this will negatively impact on the fuel consumption. The driver may notice a considerable drop in mpg; as each time the DPF actively regenerates, another dose of fuel is effectively wasted.
Additionally, on some systems where the fuel is injected on the exhaust stroke of the engine, a small but significant amount of fuel may mix into the engine oil. Over time this leads to dilution of the engine oil which has a negative impact on the running of the engine and may mean changing the oil more frequently.
All of which means that some vehicles with active regeneration systems may well benefit from the use of a DPF cleaning additive, or FBC. The additional cost of the additive may be compensated for by the improved mpg achieved due to fewer regenerations needing to occur – less wasted fuel. There is also the potential of increasing the service life of the engine oil (reducing oil changing interval).