Hello Doc

I wonder if you can clarify something for me? I have noticed that some of the fuel economy figures and CO₂ for the more recent versions of some car models are not as good as their predecessors. The differences are of the order of 3 to 5mpg, and this applies to a number of Volkswagen Group cars, particularly Volkswagens and SEATs, although I haven’t been through the whole of your data pages to see if I can find any other instances of this going on. 

It would be interesting to know what’s happening, if you could perhaps enlighten me and other readers. 

Malcolm, Torquay

I’m not sure we haven’t mentioned this before in Diesel Car, Malcolm, but I’m glad that you asked the question, as some other readers may be equally puzzled. Since what seems to have become termed ìDieselgateî, which was initiated by the exposure of some doubtful practices in US market specification Volkswagens, all the car manufacturers have been understandably anxious to cover themselves against exposure of any other doubtful practices. They have been largely successful, and some manufacturers have discreetly initiated recalls to ìimprove pollution control systemsî where engine software settings have been modified, and current production similarly updated. Following the exposures of illegal engine software, and exploitation of the flexibility in the official test cycles (in our case the European NEDC cycles), manufacturers have undoubtedly discontinued some marginal practises that they had used in testing which they saw might now be open to question.

We also have the situation where the new WLTC test cycles, that came into effect on September 1st this year for new models (September next year for all new cars), are known to produce higher emissions and higher fuel consumption figures than the old NEDC cycles. It may be that some manufacturers saw a way of reducing these fairly obvious unfavourable changes with the WLTC by cushioning the effect with relatively modest increases in the figures that will be their last ones based on the old NEDC system. We know, for instance, that manufacturers are currently allowed to declare ìofficialî emissions and fuel consumption figures up to four per cent lower than their actual test figures, for no apparent reason, and with no justification, it would seem. With that liberty to favourably adjust the figures disappearing, it would perhaps make sense for any corrections to be applied in less noticeable small steps, they may have thought. We can’t expect the difference between reality and the laboratory test results to totally disappear, but it should come down from 35 to 40 per cent to maybe 15 to 20 per cent in the new WLTC tests.

I think you can put what you have seen down to ìOne small step…î although it may be some while before we get to step onto Planet Reality. I might also say that most laws and regulations are made to be broken, and weak regulations of emissions and fuel consumption testing, with weak and ineffective enforcement, are precisely what have got us where we are today, and you can’t blame the competing manufacturers alone for that.

Doc Diesel