Are we tiring of Diesel?

Posted on February 7th, 2012 by Rob Marshall

Arising from the numerous technical enquires, received from GEM members, there appears to be mounting dissatisfaction with modern diesel cars. The blocking of diesel particulate filters (DPF) seems to be the main gripe. While this system acts as a ‘soot filter’, to prevent unburnt diesel particulates from entering the atmosphere, infinite quantities cannot be held indefinitely and so a cleaning cycle is initiated by the engine management system, which heats the exhaust system to such a high temperature, the trapped particles simply vaporise.

Yet, for this cleansing process (called ‘regeneration’) to work effectively, the engine needs to be under a steady load, which requires the car be driven constantly at speeds exceeding 40mph for at least ten minutes. If the vehicle spends most of its life being driven in town conditions, regeneration might not be able to occur, hence the illumination of an engine management lamp on the fascia, indicating that the DPF is becoming over-choked with soot.


Are we tiring of Diesel?In many cases, I direct blame at the car salesman, for failing to assess the owner’s needs and matching it with the right vehicle. Selling an elderly driver a diesel car, which is likely to spend most of its life being driven at low speeds around town, on the basis of fuel efficiency, has been commonplace. While diesel cars tend to be more economical on fuel than petrol models, the additional cost of maintaining the various anti-pollution systems is witnessing many owners waving good-bye to their fuel savings.

Mounting European legislation might also be at fault, because the environmental cost of maintaining (or replacing) a diesel engine’s emission-controlling components are not considered by the bureaucrats. As Euro V tailpipe emission regulations are dictating that commercial vans must be fitted with both DPFs and EGR (exhaust gas recirculation valves), the increased risk of unscheduled breakdowns on commercial vehicles that are used in urban conditions is worrying the fleet sector, where petrol-powered alternatives are uncommon.

John Watts, of the used van valuation organisation, CAP, used the example of a city-based, self-employed owner of a used commercial vehicle, who travels only 10 miles to-and-from work each day, as being especially vulnerable. Disturbingly, Watts suggests that these problems could spark higher depreciation rates as the Euro V-compliant van ages, highlighting that the issue will have ramifications across the entire used van sector.

However, some private motorists have acknowledged that, while modern diesel cars are considerably faster and smoother to drive than the units of twenty years ago, the trade-off has been decreased reliability. The high parts cost of not only the emission control components but also other items, such as fuel pumps, can be many times higher, when compared to those of a petrol car. Not only is petrol less expensive than road diesel but, when the overall lower purchase prices of petrol vehicles are considered, many people are realising that diesel cars can make less sense.