Audi A6 review - MPG, CO2 and Running Costs

Large executive cars like the Audi A6 are often driven by high-mileage drivers, and economy will be at the forefront of both fleet managers’ and private buyers’ minds.

Take the most powerful, 282bhp 50 TDI diesel engine. Despite being capable of a serious turn of speed, this officially returns 50.4mpg and emits 146g/km of CO2, in both Sport and S line trims. That CO2 figure means business users will be liable for a Benefit-in-Kind (BiK) rate of 34 per cent in the 2018/19 tax year. If that sounds worryingly close to the top 37 per cent rate, there are two reasons for this: one is Audi homologating the A6 according to the latest, stricter testing regime, and the other is the recent government decision to shift all diesels up a percentage band for BiK rates. 

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This rate rise for diesels means the 55 TFSI should actually get a lower BiK rating than the 50 TDI, despite having higher CO2 emissions. While precise figures may change by the time the 55 TFSI arrives in the UK, Audi is currently quoting a CO2 figure of 151g/km, which should translate into a 31 per cent BiK rate (2018/19). Whether that lower taxation level will make up for the TFSI’s fuel consumption of 42.1mpg will depend on list prices and mileage though, naturally.

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Figures for the 2.0-litre 40 TDI mean it's the cheapest A6 to run. It emits 117g/km in both Sport and S line trims, meaning a BiK rate of 28% in the 2018/19 tax year. That also translates into official fuel economy of 62.8mpg, which is virtually identical to the BMW 520d's quoted fuel economy figure.

Road tax (VED) for the A6 will span two brackets. Models that cost under £40,000 - which at the moment is just the entry-level 40 TDI Sport - pay a flat annual rate of £140, while all models costing over £40,000 – including entry-level cars with options – will be hit with a supplement of £310 for five years. This kicks in during the second year of a car’s life, bringing your annual VED bill to £450 a year from years two to six. First year VED rates remain CO2 based, and tend to be bundled into on-the-road prices.

One thing helping the A6’s efficiency is the fact all models come with mild hybrid system, which comprises a belt alternator starter (BAS) and lithium-ion battery. The four-cylinder 40 TDI gets a 12-volt system, while the six-cylinder 50 TDI and 55 TFSI come with 48-volt setups.

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When coasting with your foot off the accelerator between 34-99mph, the 48-volt mild hybrid system fitted to six-cylinder cars allows the engine to switch off, saving fuel. Similarly, the start-stop function can activate at 13mph and below, allowing the car to glide to a stop with engine-off efficiency, before the engine restarts when sensors detect the car in front moving off. Audi claims the 40 TDI's 12-volt setup works on the same principle as the 48-volt system, but cautions its efficiency savings are "somewhat reduced".

On the performance-orientated side of things, the S6 is your best bet if you wish to retain a modicum of affordability at the pumps. In saloon form the S6’s diesel engine returns a claimed average of 36.2mpg – not bad considering the car’s power, size and weight – while emitting 240g/km of CO2.

Insurance 

The 201bhp 2.0-litre diesel 40 TDI will be the cheapest A6 to insure, sitting in group 33 out of 50 regardless of whether you choose S line or Sport trim. This is a higher group than the slightly less powerful (187bhp and group 31) BMW 520d M Sport, but lower than the slightly more powerful (228bhp) 525d, which gets group 37 insurance. The A6 does better than the E-Class when it comes to insurance, though, with the 194bhp E220d sitting in group 35. 

Depreciation 

The Audi A6 has two factors that pull it in opposite directions: on the one hand, large executive saloons tend to lose value relatively savagely; yet on the other, Audis have a strong reputation for residual values. The A6 has residual values after three years in the 41-46 per cent range, which is similar to the BMW 5 Series, with the Mercedes E-Class and Jaguar XF both very marginally ahead.