The Audi A6 2.0 TDI is the most popular choice among saloon and Avant buyers. It does not offer the best blend of performance and economy in the class, but when that class includes the BMW 520d, that is no disgrace. And it runs the 5 Series extremely close and has the measure of all other selected rivals, Mercedes included. It shows how far Audis have come from the day when almost all their draw came from their showroom appeal.

The four-piston motor may be an entire litre shy of anything else you’ll find under the bonnet of an A6, but in no way does it feel like a poor relation. Far more refined than an equivalent Mercedes unit, again it bows only to BMW for the civility of its operation. It sounds a little rattly first thing on a cold day, but that’s the only time you might wish there was something other than diesel in the tank.

The 2.0 TDI is so good, it asks serious questions of the rest of the engine line-up. Few cars can do that

Strong acceleration is available from 1600rpm, and the car stays in the thick of the torque curve until nearly 4000rpm. In fact, the opportunity for a near-perfect flow of power is there to be taken and denied only by its gear ratios. Even as it is, the A6 will motor promptly to 60mph in 8.9sec and, if you keep your foot buried, not stop until it’s showing the far side of 140mph. 

The 3.0 TDI’s V6 engine starts with a gentle shudder; once you’re cruising you’ll barely hear it. That’s partly because Audi’s twin-clutch gearbox is quick to change up, keeping revs low whenever possible, but mainly because Audi’s done a stunning job of insulating this car’s powertrain. Wind insulation is very well suppressed too, thanks to a low drag coefficient of just 0.26.

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