Ask The Expert

Would a DPF flush clean lead to possible contamination of the engine oil which might necessitate an oil change?
Vijitha, UK

I doubt that a ‘DPF flush clean’ would cause engine oil contamination. As far as I’m aware, most of these types of fluid treatments are applied through a pressure sensor port close to the DPF. This is downstream of the turbocharger, which would be the only part of the exhaust system where contact with engine oil could take place. Therefore I wouldn’t expect engine oil contamination to be possible.

However, it may be possible that the engine oil could become contaminated as a result of DPF blocking problems. Some vehicles use ‘active regeneration’ to combat soot build up, this involves a post-combustion fuel injection into the exhaust stream. This acts as a sort of ‘lighter fluid’ to initiate soot burn off in the DPF. Depending on the set up, some vehicles simply inject fuel on the exhaust stroke of the engine. If this is happening very regularly  due to DPF blocking problems, then there is a possibility that the oil may become contaminated by fuel.

So it could be that the circumstances leading to someone using a DPF flush clean may necessitate an oil change.

What is the best DPF additive or FBC on the market today?
Patrick, U.S.

I note that you are in the US so assume your question relates to your home market. My knowledge of the US market for DPF Additives is not as thorough as in Europe where these products have become important due to the high proportion of passenger diesel cars.

Any effective DPF Additive should contain an FBC as the active ingredient and Cerium, Platinum and Iron chemistries are the most common. All are metallic. In the US it is difficult to register metallic fuel additive chemistries for ‘on highway’ use due to EPA regulations so this limits the availability of DPF Additives. My best advice is to see if you can find a product called DPF Cleaner or DPF Regenerator and try to verify that it has a credible FBC in the formulation by looking at the Technical Data or other product information.

In general I believe the best DPF Additives on the market are those that contain a high dose of Cerium due to certain technical performance advantages. I hope that is helpful.

Hi, What is your opinion on the most effective FBC? I have a 59 plate Mazda 1.6d which has the Ford PSA engine and uses eolys fluid. I believe this is cerium oxide. Is iron oxide or platinum oxide a more effective FBC? I'm not sure if this PSA engine also uses post injection to heat the exhaust gas, would you know? Regards, Ady
Ady, Torquay

Thank you for your questions. I believe the most effective FBC is cerium oxide because it is a catalyst for soot removal by both oxygen and nitrogen dioxide gases in the exhaust. This is not true for iron and platinum so they are less effective. Over the years there have been 3 generations of Eolys fluid which have used both cerium and iron chemistry. Your car uses Eolys 176 which contains both iron and cerium oxide. The PSA literature suggests your car does have post-combustion fuel injection but I don’t know for certain.

I'm not a chemist but a physicist. Can you tell me the chemistry of soot (carbon) removal from the DPF? Is the end product of regeneration not carbon dioxide? If so, are we not swapping one problem for another, or is the carbon dioxide yield trivial compared to that produced elsewhere in the engine?
Stan, Stroud, Gloucestershire

The exact chemical pathways may be complicated, but essentially you are right that regeneration involves the combustion of carbon-based soot to produce carbon dioxide (which is a greenhouse gas). However, it is not really swapping one problem for another because (a) the amount of carbon dioxide produced is tiny compared with that from the useful fuel combustion in the engine and (b) soot pollution can also contribute to global warming anyway.

But more importantly, it should be stressed that exhaust aftertreatment devices such as DPFs are primarily concerned with reducing local pollutants (those which are damaging to human health) rather than greenhouse gases. The DPF in particular is used to prevent particulates (soot) being emitted from the vehicle, which are implicated in a number of health concerns including asthma, lung problems and increased cancer risk.

Is there a difference between a DPF additive and DEF?
Diane, Edinburgh, UK

The short answer is – yes!

DPF additives are often added straight into the vehicle’s diesel fuel tank. Some vehicles have a separate tank for a DPF additive which needs topping up occasionally to work with a specific DPF system. They contain chemicals called Fuel Borne Catalysts (FBCs) which are carried through the combustion process and into the exhaust system. Once there, they enter into the Diesel Particulate Filter (DPF) and help to burn away the soot which is collected and which can sometimes lead to problems with DPF blockage. You can find out more about FBCs on this page: FBC Chemistry

Diesel Exhaust Fluid (DEF, also known by trade names such as ‘AdBlue’ (a trademark of the VDA)) should definitely not be added to the fuel tank. DEF is a specially made solution of urea in water which is held in a separate tank on board the vehicle. It is released directly into the exhaust system (post-combustion) and works with a Selective Catalytic Reduction (SCR) system to lower the NOx emissions in the exhaust. You can read more about this and other technologies to reduce diesel emissions here: Other Technologies

Why has the DPF light on my dashboard come on?
Dave, Bristol, UK

The DPF warning light is an indication that there is a problem with the Diesel Particulate Filter (DPF) in the exhaust system. The most likely cause is that the DPF has accumulated too much soot which is causing back pressure on the engine. The soot needs to burn away to clear the filter (a process known as Regeneration). This will happen when the exhaust gas is hot enough. It’s a good idea to act quickly in this case to prevent the filter becoming even more blocked up (such that a trip to the garage is necessary). A ‘fast’ drive will help to get the exhaust temperature up; 40mph (60km/h) for 15 minutes or longer (engine speed about 2000 rpm). The process may be helped by using a reputable branded ‘DPF Cleaner’ fuel treatment, which contains chemicals that help soot to burn.

You can find more information about the possible causes of DPF problems on this page: DPF Problems – Possible Causes

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