The Rise and Fall of The Diesel Engine

It seems sales of Diesel engined cars has slumped dramatically. No wonder really, as diesel engines have suffered a a series of knockbacks in recent years. This after successive governments and enviromentalists have said that Diesels are better than petrol engines, having focussed solely on CO2 emissions rather than emississions in the round, ignoring the particulates and NO2 that diesels produce. Favourable tax breaks have promoted Diesel cars in favour of petrol in the fleet market by a significant amount. Try and find a used medium sized petrol car from the past 10 years and you'll probably find they are outnumbered by Diesels 2:1.

But after all that promotion, tax breaks and environmental good will, the Diesel car has crashed sales-wise in spectacular fashion. For a number of reasons. One of the main ones is the risk of a change in the favourable tax structure suporting Diesels and also the risk of being locked out of clean air city centres in the future.

The VW scandal showed how difficult it was for manufacturers to make a diesel-engined car that met tough emissions tests and still drove well. EU emissions standards thrown down for manufacturers to meet in a ludicriously short time threw up a number of issues. From inappropriate installations, clogging particulate filters, self-destructing fuel pumps, additive issues, driveability issues (which led to  manufacturers using software routines in the ECU to detect testing scanarios and use a different ECU map for the tests as opposed to real-life driving).

Owners of older cars are finding that diesel-engined cars have problems all of their own and modern, high-pressure direct-injection diesel engines are horrendously fragile and expensive to maintain: in some instances the very fuel they use destroys the engine!

Examples of inappropriate installations are diesel engines in small town cars, that hardly ever get run on motorways. The Diesel Particulate Filter fitted in the exhaust which is required to meet EU emissions standards needs to run at a high temperature in order to turn the particulates to less harmful ash. Town cars or diesel cars doing short journeys never get up to anywhere close to those temperatures and so the DPF clogs up. Replacing the DPF can cost around a thousand pounds, a significant proportion of the cost of the car once it hits the used market.

High pressure direct-injection diesel engines rely on complex high pressure pumps to inject diesel fuel into the cylinder when the pressure is it's greatest. That's makes the engine very efficient. The problem is that at the pressures we're talking about (over 1000 psi), the pumps need very good lubrication. They are designed to use the diesel fuel itself to lubricate the pump. At these enormous pressures, any deviation from pure diesel, can have a catastrophic effect on the lubrication qualities of the fuel. For instance higher levels of biodiesel mixed with regular diesel can affect it's lubrication properties to such an extent that injection pumps eat themselves and fail. Another mode of failure is cavitation inside the pump as it works. Again any change in the fuel formula affects the cavitation restance and eventually the pump destroys itself as it works. 1000 psi pumps are not cheap items to produce and are horrendously expensive to buy. New ones can run to around £1000, again making used diesel engined cars almost a throw-away item.

The drive to tax diesel cars more, or refuse them access to clean air zones in cities means that mixed messages are reching the car-buying public, around the same time the used market are getting wise to the extreme costs diesel cars can rack up. They're becoming the leppers of the car world.

Since 2001 there have been ever tighter standards legislation pushed onto the automotive industry and manufacturers have been pushed to their limit trying to keep up. That's not to say they haven't used the changes in standards and manufacture to their advantage.

I have a 1999 car as I won't buy one younger than 2001, nor will I buy a modern diesel-engined car. Why is that? It's because newer cars get increasingly complex, so much so they become difficult and expensive to maintain outside the dealer network. My car has fuel injection, electronic engine managament, ABS, and even a fly-by-wire throttle (by far the weakest part of the car as they are known for failing).

Modern cars go even further, with each item in the car having it's own control module. For instance electric power steering: the steering will have it's own control module. BUT the manufacturer codes that unit to the car, but if it fails you can't just buy a used unit from another car and swap them over. Because the code will not be the same, the unit from another car is rendered incompatible. Not from a hardware standpoint, but it is deliberately coded in software so a unit will only work in a particular car and no other, rendering the used spares market difficult at best. These days there are companies that have cracked the codes and offer re-coding services, but not all modules are crackable and the re-coding service isn't cheap, pushing up the price of used parts.

Another area is where something should be user-serviceable, but the manufacturer deliberately makes it dealer-serviceable only. For instance in certain diesel Peugeots, they carry a tank of additive to improve emissions. If you have seen tubs of "Adblue" on petrol station forecourts, it's the same stuff. It's injected along with the diesel to help emissions.

However, rather than have a level gauge like a fuel tank, the cars computer is linked to the fuel tank filler cap. It counts the number of times the filler flap is opened and then calculates the amount of additive that would have been used for a FULL tank. Obviously if you part-fill the tank you use less additive. So you eventually get to a situation where the computer says the additive tank is empty (as calculated by filler flap openings) but you may actually have half a tank left. No problem, just top up the tank eh? Nope! It's a dealer-only service! There is no filler cap. You have to pay a dealer to fill up a tank you can't yourself even though the additive is freely available. And only the dealer can reset the computer to say the tank has been filled.

Again there's an evolving aftermarket working to deal with these issues, but why does it even have to happen? A small tank with a fuel gauge or a warning light and a filler cap just like a washer bottle should suffice.

But no, as with the coding issue I've already mentioned, dealers are turning new regulations and standards along with new technology to their advantage.

It's this mechanical complexity, poor after sales support and unfair use of new standards and technolofy that car buyers are railing against.

Small modern diesel-engined cars are unfit for purpose. Unless you rag them along the motorway every couple of weeks then eventually the DPF will block up and you will end up with a big bill.

If a fuel supplier puts more biodiesel on the mix, then the diesel high pressure pump dies, with (you guessed it) another big bill.

If a part wears out, you can't swap a used part from another vehicle to the car, with yet another big bill to replace the part.

It's this that is putting new car buyers off. I'm sure that most small diesel buyers are waiting for electric car technology and it's support infrastructure to mature and will probably jump to either an all-electric car, or if they can't wait a petrol-electric hybrid.

However, like all modern cars, these also have their pitfalls along the way, especially battery life and replacement cost later on in life.