The great diesel con exposed: It's time we ditched these expensive, dirty, inferior vehicles

At last, someone is talking sense about the Great Diesel Con. Diesel cars, I have been saying for years, are expensive, inefficient, dirty and unreliable compared to their petrol equivalents. This contradicts just about every piece of received wisdom concerning motor fuels.

People buy diesels because they think they are more fuel efficient than petrol cars. As a new Which? Report out this week confirms, while this is (marginally) true, overall the economics are mostly in favour of gasoline. This is because - believe it or not, and even in the era of the £6 gallon - slight differences in fuel efficiency really are not a big factor in the overall cost of motoring.

Which? has calculated that for an average British motorist the extra outlay to buy a diesel – typically £1000-3000 more than the petrol equivalent – will take more than a decade, if ever, to be paid off by fuel savings (especially as diesel is now significantly more expensive than petrol). Only people who do very high mileages (more than 18,000 annually) and who wish to drive a big luxury car (where the efficiencies of diesel start to count) may find diesel saves them money.

For the average British motorist the extra outlay to buy a diesel ¿ typically £1000-3000 more ¿ will take more than a decade to be paid off by fuel savings


There are other reasons to avoid this dreadful fuel. Firstly the modern diesel engine is unreliable. This is largely down to one thing: the particulate filter which must be plumbed into the exhaust system to stop these cars belching the clouds of lung-clogging smoke that we associate with grease-burning engines.

In slow town driving these filters can become blocked, shutting down the engine. Manufacturers say that a long blast down the motorway will cure the problem, which may be true, but this isn’t much good if the car is too sick to get to the motorway or if you are stuck in the middle of a city.

Modern diesels are highly-tuned pieces of precision engineering, impressive in their own way, and I have driven some diesels that are extraordinarily smooth and powerful. But this precision makes them very prone to driver error. Put a few litres of diesel in your petrol tank by mistake and you will probably be fine. Brim it with unleaded and you may notice a bit of stuttering but eventually all will be well, no lasting damage done.

But put petrol in a diesel tank by mistake and you may well kill your car. The injectors used in diesel engines run at extraordinarily high pressures – several tens of thousands of pounds per square inch – and the pumps rely on the natural oiliness of diesel as a lubricant. If you slosh some gasoline, which is much thinner and less oily, into the tank and do so much as turn on the ignition (or even, in some cases, plip the door locks) the pumps will start to prime themselves, shredding their insides and leaving you with a bill for thousands.

This didn’t happen on old diesels which were agricultural affairs, but on new ones the fact that a single silly mistake at the pumps could be enough to destroy your car beyond economic repair is, surely, reason enough to avoid this awful fuel.

More reasons to shun diesel: They are not as clean as the makers claim. I cycle a lot in London and can attest that even shiny modern diesel cars emit periodic bursts of black, suffocating smoke that would do a 1960s Bedford lorry proud. They are, as Which? says, more expensive to buy and probably more expensive to maintain than gasoline cars.

So why are diesels so popular? Part of the reason is that car buyers have been seduced by the fuel-economy myth, the one which states that consumption is the major cost of motoring. If you buy a new or even newish car this is massively not the case; the major cost, outweighing all others, is depreciation, a figure which the manufacturers NEVER want to talk about (unless the manufacturer is Morgan or Ferrari, whose cars do not really depreciate).

Spend £20k on a new mainstream car and you will lose several hundred pounds a WEEK in the first year of ownership. This alone makes differences in fuel consumption, even the difference between 20mpg and 60mpg, more or less irrelevant. Car makers like diesels because the profit margins are greater and in the 1980s and 90s the major European manufacturers invested billions in diesel technology (backed by subsidies from, among others, the French government) believing this fuel to be the future.

My guess is that diesels are on the way out. A few years ago there probably were arguments in their favour, for high-mileage drivers of, as I said, large powerful cars. But petrol-engine technology is advancing in leaps and bounds. By 2022 I would guess the diesel may be more or less extinct (along with Hybrids, but that is another story). And good riddance.