How are DPFs damaged by repeated short journeys? Our 2000 BMW 320d has done 180,000 miles without fault.

Regarding latest EU emission regulations for diesel engines, could you please give us more information on the subject of the particulate filters being adversely affected by repeated short journeys? I have got some information from the web, but it is somewhat confusing when you start to read about various manufacturers' methods of clearing the particulate filters and the possible dilution of engine lubricating oil. We have run a 2000 BMW 320d tourer for 180,000 miles without problems, with frequent short journeys due to living in a very rural area as well as shopping etc. We were seriously considering purchasing another modern diesel-engined vehicle, but since reading that piece we are very confused.

Asked on 24 December 2010 by EL, Hoath, Canterbury

Answered by Honest John
A diesel particulate gathers the black smoke you used to see when starting up a diesel, then burns it off at very high temperature later in the car's journey. It cannot do that if there is no 'later' and the exhaust system of the car does not get hot enough. Generally you need to do more than 10 - 15 miles and more than 20 miles in the winter for a DPF to start to regenerate. The vehicle cannot be used for a succession of short runs from cold.

Diesel now only makes sense for very high mileage drivers doing 20,000 miles a year or more, because over six years the cost of replacement DPFs, EGRs, DMFs and turbos otherwise outweighs any savings in fuel over a petrol engine.
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