They had neither the refinement, nor the performance to be a viable alternative to a larger, multi-cylinder gasoline engine.
All that is changing. And one of the ones helping to change it is the 2015 Audi A3 Sedan, available with the Volkswagen group's latest TDI diesel unit later this year.
We're yet to see what kind of mileage figures the car will return, but The Car Connection's early drive in a brace of gasoline A3 sedans suggests it'll be both fun and frugal.
The upcoming diesel unit is an all-new engine, designated EA288 within the Volkswagen group. It's two liters in displacement and develops 150 horsepower--10 hp up on the previous TDI.
There's also a healthy 236 lb-ft of torque, which as any existing TDI driver knows is the key to the model's performance and great highway economy.
Strong low-down torque means plenty of acceleration from low revs, rather than venturing high in the rev range and using more fuel. It also means the car can pull longer, highway-friendly gear ratios.
It incorporates high pressure and cooled low-pressure exhaust gas recirculation (EGR), integration of the water cooled intercooler and EGR valve with the intake manifold, and a combined diesel particulate filter and catalyst--mounted close to the engine to improve warm-up time.
VW and Audi have also worked hard to reduce internal friction and vibration--the latter handled by a balancer shaft.
The Car Connection notes impressive performance from both 1.8 and 2.0-liter gasoline units, sure to be replicated by the diesel. It's also described as strong, sturdy and precise to drive--all qualities familiar to existing Audi buyers.
When it arrives in the U.S, the diesel model will be auto-only, with a six-speed S Tronic dual-clutch transmission. We're looking forward to driving it--and highway economy should be in the forties.