You might wonder then why so few carmakers have mixed the best of both worlds in a diesel hybrid.
One company that has is Mercedes-Benz--and we've now driven the fruits of its labor, the E300 Bluetec Hybrid.
How it works
The Mercedes-Benz E300 Bluetec Hybrid operates differently from the last diesel-electric hybrid we tested, the Europe-only Peugeot 3008 HYbrid4.
In the Peugeot, a 2.0-liter diesel four-cylinder supplied power to the front wheels, while a rear-mounted electric motor supplied the back wheels, in a part-time all-wheel-drive format. This is known as a "through the road" hybrid system.
Mercedes' diesel-electric hybrid is more similar to traditional petrol-electric setups, where an electric motor is mated to the engine. Like the Infiniti M Hybrid and BMW's ActiveHybrid 5, the Mercedes uses a traditional automatic transmission (seven speeds, in this case), rather than an e-CVT planetary gearset like Toyota and Ford hybrids.
With a 20 kW (27 horsepower), 184 lb-ft electric motor providing assistance, the E300 uses only a relatively small 2.1-liter, four-cylinder turbodiesel to provide motive force. This develops 201 hp and over 368 lb-ft of torque (from only 1,600 rpm), though as usual you can't just combine the electric and diesel outputs for a total figure.
How it looks
There's little externally to signal the car's hybrid drivetrain. The only giveaways are relatively small wheels--wrapped in chunky low rolling-resistance tires--and a "Bluetec Hybrid" badge on the trunk lid.
Otherwise, it's standard Mercedes-Benz E Class: An imposing, Germanic profile, large grille with three-pointed star sat atop, and a slippery drag coefficient of only 0.25, thanks to careful surfacing.
Inside it's all standard E Class too. The interior is luxuriously-appointed, spacious, and feels like it will last for a thousand years. Virtually everything can be adjusted to find your ideal driving position, and you'll want for very little equipment.
A large display in the center of the dashboard can be set to display the hybrid drivetrain's status, as well as other standard functions, like navigation and audio.
How it drives
Suffice to say, the combination of diesel and electric power is a smooth, refined and punchy pairing.
In fact, it's hard not to believe there's a six-cylinder turbodiesel under the hood, such is the refinement of the car--more than a match for other hybrid luxury sedans in the class, including the BMW ActiveHybrid 5 and Lexus GS 450h.
Mercedes quotes a 0-62 mph time of 7.5 seconds, and a top speed of around 150 mph. We tested neither the former nor the latter, but both are believable figures given the ease by which higher speeds are reached.
There's little in the cabin to give away the car's means of propulsion, save for the tiny electric motor assistance gauge swinging away in the instrument cluster, and the tachometer occasionally registering zero rpm. Drive selection is handled by a tiny lever, no bigger than you'd expect for a cruise control lever, just behind the steering wheel.