All I can give is an opinion based on my own experience; I'm not saying I am right, just trying to be objective. My past is as a farmer and as such I spent a lot of time around diesels. In the 1980s tractor technology began to accelerate as turbochargers were developed as additions to extremely reliable diesel engines. Diesels were reliable because they were essentially self contained. Once started, a diesel could operate without the assistance of a battery or an electrical system. A diesel engine traditionally has a long stroke - the distance between top dead centre and bottom dead centre. This gave them high torque and a low RPM, 3,000 as opposed to 7 or 8,000 rpm for a petrol. This made them reliable, as they rotated less often in a lifetime and because the parts had to be over-engineered to withstand the high compression ignition. Turbos meant that smaller, lighter diesels could be used for the same power output. A 1980s turbo diesel required revving to 1800 rpm for 1 minute at a standstill before stopping to cool down the turbo. I cannot recall hearing of a failure in this if it was properly respected. Many farms fitted after-market turbos to standard tractors and I heard several tales of transmission and gearbox failures because of the extra power, but never the engines. The first cars were equiped with diesels at this time, and farmers were the main clients as they realised the reliability factor in a diesel engine. Unfortunately the technology didn't lend itself to automotive use as the units were naturally aspirated and very heavy. I had a 1980 Ford Grenada 2.5D and still remember the heavy steering and poor performance today. Then came modern turbos, intercoolers, "DI" direct injection, common rail and electronic engine management, all of which has transformed automotive engines, petrol and diesel. Undoubtably diesels have seen the most technological advances, and of todays units, the Nissan 2.2 dCi is a good example. As such, a modern diesel is no longer capable of running independently of a source of electricity, but modern electronics has also hauled even petrol engines to new hights of reliability when compared to the old rotating points technology. I don't believe a modern automotive diesel is intrinsically more reliable than its petrol counterpart today, but there is one hell of an advantage. Next time you're doing 70 down the motorway in your Xtrail, look at the rev counter and you'll be doing about 3,000 rpm. When you think its petrol counterpart would be doing nearly twice that, it has to be a better bet for reliability, even with any tweaking you might do. Also, the lubricant contains a detergent. Petrol lubricants don't, and allow a build-up of sludge. When you take a diesel apart, it's always a wonder how clean everything is, in spite of the oil being black. Different worlds.
