One of the main criticisms about compression-ignition engines in the 1980s was loudness. Although there were other issues, such as bad odor smoke

Since that time, a lot has changed. For one thing, rather than its price, fuel availability was more of an issue during those periods of the energy crisis 

The new 3.0 liter V-6 turbo-diesel engine in this Mercedes ML also makes a strong argument for quiet. It is silent throughout its whole power band, with the exception of a slight rattle at starting.

These noise contrasts appear to be fairly close together, but keep in mind that now the decibel scale has sharp increments since it is logarithmic.

Due to packaging constraints, it has a DOHC 24-valve 72-degree V-6 arrangement rather than the traditional 60-degree layout, and it utilizes a balance shaft to dampen primary vibrations.

One of the secrets to the engine's silent functioning is the direct injection, which employs one 8 vibrating injectors in each cylinder and delivers two to five spritzes every power stroke.

The Garrett turbocharger increases combustion-chamber pressure by forcing air through with a Behr air-to-liquid intercooler; the maximum boost is reported as 1.45 bar (21.0 psi).

This 2.5-ton luxury SUV, which is 239 lbs lighter than the ML350, can reach 60 mph in 8.1 seconds, which is one full second than the 268-hp petrol model.

Of course, diesels also have to do with fuel efficiency, and the verdict is yet out on that front. Mercedes mentions traveling the 639 miles from Michigan to New York on a single 25.1-gallon tank.

But at the 19 mpg consumption rate we saw, you'd have to walk the final 162 miles.But at the 19 mpg consumption rate we saw, you'd have to walk the final 162 miles.

However, 19 is still 2 mpg more than we got with the ML350. Additionally, it's important to note that my man Gillies documented

driving a similar ML320 CDI in the UK last summer, I got over 28 mpg. You won't see this one coming, but that much is clear.