There was a time when diesel engines were lumpy, loud, lazy — and everlasting. All that has changed in the past 10 years.
Today’s automotive diesels are refined, quiet, powerful — and perishable. How did this happen and how can you keep the diesel engine in your car from packing up prematurely?
These were the questions I put to staff at the foremost diesel workshop in my area during a recent interview.
The revolution in automotive diesel engines came about through electronic injection control (combined with common-rail fuel supply) and turbocharging. The objectives were cleaner emissions and better fuel economy, coupled with in- creased power on demand.
Considerable advances have been made on these fronts. But there are no gains without pains. And the pains in this case come from the greater complexity and sensitivity of the components. This means that enormously expensive equipment is needed to achieve the extremely fine adjustments required to set up the injection system correctly.
At the workshop where I had the interview, a “clean room” (with filtered air) was being installed, containing measuring equipment costing R1.5-million which allows adjustments to an accuracy of one micron — that’s one- thousandth of a millimeter, smaller than most bacteria.
At the pressures found in modern common-rail systems (1 800 bar and higher), one micron bigger or smaller is important. Equally important is the training and mindset of the technician working on the injection system. This is not a job for amateurs — that’s probably the most important thing I learnt from the interview. The worst thing you can do to a modern diesel is to let a half-baked mechanic tamper with it. If anything has to be done to the injection system, make sure that the vehicle is taken to a fully-equipped, specialist diesel workshop.
The turbocharger, now almost universally fitted to automotive diesels, presents its own set of problems. The turbine vanes on variable- geometry turbos must swivel in a precisely controlled fashion to regulate the boost pressure.
However, the turbine wheel spends its life in a stream of exhaust gas — at times reaching temperatures of 700°C — laden with soot particles. Wear to the spindles on which the vanes rotate is inevitable, followed by lost motion, over-boosting and the onset of the dreaded “Limp Home” mode.
There’s nothing an owner can do about this — the symptoms will normally appear at around 200 000km.
What you can do is to ensure that the turbocharger doesn’t pack up before then, and here good quality oil is important, as is the practice of letting the engine idle for a minute or two after it has worked hard, before switching it off. This allows the cooler exhaust gas produced during idling to cool off the turbine wheel and thus lessen heat soak into the shaft and the surrounding oil.
This practice can make an appreciable difference to the service life of a turbocharger.