Audi Q7 V12 TDIMany of VW Group's best diesel SUVs were good because they were sensible and economical while retaining power. The Audi Q7 V12 TDI managed to be the last of those things, but it completely forgot about the other parts. It's the only diesel V12 engine ever put into series production, and there's a good reason for that. Rather than starting life as a road car engine, the V12 under the hood of the Q7 was originally designed as a racing engine. It was built for Audi's R10 endurance race car, and proved very effective. It was so effective, in fact, that it won the 24 Hours of Le Mans three times consecutively between 2006 and 2008.Originally, Audi bosses reportedly planned to build a diesel version of the R8 supercar to bridge the gap between the brand's racing efforts and its road cars. However, that proved too expensive, and so engineers came up with the idea of putting it in the Q7 instead. The result was a luxurious, family-hauling SUV with 493 horsepower and 738 lb-ft of torque. It was a completely unique and hilariously overpowered car, but also an extremely expensive one. Its price tag when new eclipsed $100,000, and as a result, it sold terribly. However, buyers today have no problem shelling out significantly more cash for a top-spec RS Q8 or one of the many other ultra-high-end SUVs out there, so why not bring back the most outlandish diesel family hauler ever made?Bentley BentaygaThe short-lived diesel Bentley Bentayga offered similar levels of power and refinement to its W12-powered counterpart, but with greater fuel economy and more torque. It was eventually discontinued and replaced by a hybrid gas powertrain option, with the brand noting that at the time of its axing in Europe, there were zero orders on the waiting list for one. Clearly, it didn't sell as well as the brand had hoped.This was likely more down to image issues than any issue with the powertrain itself. The diesel V8 engine that the Bentayga used was sourced from Audi, which also offered it in the cheaper SQ7. The other engine option for the Bentayga, the W12, was exclusive to Bentley, although it was also considerably pricier. That didn't seem to put off buyers, who were already shelling out six figures on the car, and so didn't think twice about paying a further premium for the extra cylinders. That's a shame, as there was little to dislike about the diesel Bentayga, even if it didn't carry the same purebred image as its W12 sibling.Volvo V90Volvo seems to still be toying with the idea of whether or not to discontinue its V90 estate, but the diesel version is long gone. It was a very sensible (some would say boring) car, but for long-distance commuters looking to save at the fuel pump without compromising on power or comfort, it remained appealing right until its demise. Rather than quietly discontinuing its diesel lineup, Volvo announced with some fanfare in 2024 that it had built its last diesel engine and was focusing on electrification.According to the brand, it was simply the financially sensible thing to do, as European buyers were no longer buying diesels and had previously been the brand's largest diesel market. Still, in the same press release that announced the end of its diesel range, it highlighted its previous diesel plug-in hybrid V60, which could drive more than 600 miles without needing to refuel. A V90 diesel plug-in hybrid would surely offer even more range, plus the superior efficiency of a diesel engine, but Volvo opted to make its current Euro-spec V90 plug-in hybrid gas-powered instead.Audi S4 TDIDiesels aren't generally thought of as being fun to drive cars; instead, they are more about saving fuel. However, the Audi S4 TDI proved that buyers could have the best of both worlds. It remained in production until 2024, when Audi's confusing switch-up of its naming system saw the previous S4 become the S5 and lose its diesel engine in the process. Before it was axed, the diesel S4 offered around 350 horsepower and 516 lb-ft of torque, which was enough for a 0-62 mph time of 4.8 seconds. Its top speed, like many German performance cars, was limited to 155 mph.Its performance didn't compromise its efficiency, with the diesel S4 reportedly able to achieve 40 mpg during everyday driving. It didn't compromise its practicality either, with the S4 still sporting the same general dimensions as the more everyday A4 sedan. Its discontinuation can be attributed to the general drop in demand for diesel cars in Europe, rather than any shortcoming of the car itself.
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