A Diesel Alternative

Some say GM’s long-ago failed experiment in converting V-6 and V-8 gas engines to diesel is to blame for the average American’s aversion to compression ignition. But even the best oil burners that gained some U.S. popularity in the wake of the ’70s gas crisis were rough, noisy and smoky and required an annoying wait for glow plugs to warm. And the fuel smelled badly on your hands.

The 201 hp 24-valve 3.2L inline 6-cylinder turbo diesel utilizes the latest diesel technology to deliver plenty of power, great fuel economy and a whomping 369 lb.ft. of torque.

Now, following a long absence here and enormous growth in Europe and elsewhere, diesels are back in North America in limited volumes just as gas has gotten a little more dear. Compared to those in our memories, they are relatively quiet, surprisingly smooth and powerful and essentially smoke free, and this shining mid-range Mercedes example is capable of converting many to diesel addiction.

Besides prodigious torque and impressive economy, this turbocharged 24-valve 3.2L inline six achieves far lower emissions than previous- generation diesels largely due to high-pressure full-electronic injection, which until recently was considered technically impossible.

CDI stands for Common-rail Direct Injection, through which the fuel line loop supplies very high (up to 23,000 psi) constant pressure to each of the six solenoid injector valves.

While diesels produce more oxides of nitrogen and particulates than gas engines, they typically emit significantly lower CO and 20-30 percent lower CO2. With precise electronic control of fuel delivery and oxidation catalysts, the E320 CDI passes emissions in all states except California and four others that adopted its stricter standards. M-B says its engineers are optimistic that they can meet still tougher 2007 U.S. requirements when low-sulfur diesel fuel becomes available here late in 2006.

Standing on the right pedal demonstrates one good reason why modern diesels have become so popular in other markets. Once the (somewhat lethargic) electronically controlled 5-speed automatic gets around to responding, this $50K luxo-sedan accelerates like a rocket, and the shifts are smooth enough to disguise the 201-hp, 369 lb-ft diesel’s relatively narrow torque band. We used only about 5/8 of the tank and saw 28-33 mpg in a week and 409 miles of mixed city/highway driving. The E320 CDI’s EPA economy is 27 City, 37 highway vs. the gas-engine E320’s 19/27, and it blasts from rest to 60 mph in 6.8 sec. vs. 7.1.

Electronic control of fuel injection also enables softening of the power pulses to smooth and quiet the engine, even at idle. You still hear the engine’s characteristic growl, especially at idle and low operating speeds, but it’s far from the nasty marbles-ina- jar racket of old.

Mercedes debuted the world’s first diesel passenger car — the 260D — in 1936. Today, diesel engines power some 40 percent of M-B passenger cars worldwide. More than 75 percent of M-B’s North American passenger cars were diesel powered In the 1980s, but they tapered off through the ’90s until the last one, the E300 Turbodiesel, disappeared in 1999.

Now this one is back, and it’s a gem. The fuel still stinks when you get it on your hands, but we’re told the low-sulfur diesel won’t. Let’s hope not, because it’s hard to find much else to dislike about today’s ultra-sophisticated diesels — except that they’re expensive relative to gas engines. And meeting ’07 emissions standards (if possible) promises to make them more so.