Gas vs. Diesel

If there’s one word that most people associate with older Mercedes, it’s “diesel.” A few years ago I owned a 1980 450SL convertible. During the 1970s, the 450SL was nearly everyone’s dream sports car. I’d get offended about once a month when someone would ask if me if my car was a diesel. Sometimes I shoot back: Do you really think they’d put a diesel in a sports car?

All these conversations just show my own ignorance. The fact is, diesels are no longer the slow, smelly, noisy, clunky oil burners that they used to be. And yes, they really do put a diesel in a sports car. You can can even buy an SL400 CDI in Europe. If it hadn’t been for General Motors ruining the public’s perception of diesel motors, we’d probably all be driving diesels today. Modern turbodiesels — like the ones available in the E-class — often outperform gas (petrol to you Brits!) engines of the same size!

If you’ve never driven a turbodiesel, you’re in for a treat. Most passenger car engines today are designed for maximum horsepower at the expense of torque. Torque is what accelerates your car, not horsepower. Diesel engines build most of their torque at low RPMs, whereas gas engines must be wound out to get moving in a hurry. The difference between diesel and gas engines is like the difference between tractor engines and weed whacker engines.

In a turbodiesel, the feeling of acceleration is like the feeling of taking off in a jet airplane. The car builds speed like it’s attached to a giant rubber band. Just a little squeeze of the accelerator pedal is all it takes to shoot forward. To get the same response out of a gas engine, you’d have to nearly floor it.

Turbodiesels offer better gas mileage and much better performance in everday driving conditions than gasoline engines. Gas engines are more powerful at high RPM, so they’ll usually win the top speed shootouts. But who spends most of their time near redline?

W210 Diesels

Okay, you’ve sold me on diesels. Can I get one in the W210? Mercedes sold a diesel in the W210 in the U.S. for four years: 1996-1999. During the first two years, 1996 and 1997, the E300 diesel was offered without a turbo. This OM606 engine was carried over from the 1995 W124 E-class. It only produced 134 HP and 155 lb-ft of torque. Without the turbo, acceleration is — to borrow a term from Rolls Royce — adequate. Figure about 11-12 seconds 0 to 60. You won’t beat anyone at the stoplight drag strip. But you won’t get run over on the freeway either. The naturally-aspirated 1996-1997 has plenty of power to cruise on America’s highways as long as you keep it under 100.

In 1998, Mercedes turbocharged the OM606 engine. The extra air from the turbo bumped up the horsepower by 30% to 174 HP and the torque by 57% to 244 lb-ft. 0 to 60 times dropped to about 8 seconds. Remember that the turbo has to spool up to get on boost. A good portion of that 0 to 60 is spent below parking lot speeds, waiting for the turbo to wind up. Once the turbo kicks in and you’re moving, say from 20 MPH on up, I’d expect the E300 Turbodiesel to smoke an E320 and keep up with an E430.

Unlike a gas engine, turbocharging a diesel does not shorten its life. The turbo actually helps the engine by reducing exhaust gas temperatures.

If driven carefully, both turbo and non-turbo diesels should return around 35-36 MPG on the highway and 24-26 MPG in the city.

Diesel Economy

Mythical Fuel Savings

The decision to purchase a diesel W210 should not be made on the basis of fuel savings. The turbodiesels are about $5,000 more expensive used than comparable E320s. To come out ahead financially, you’d first have to recoup through fuel savings your initial $5,000 outlay. The numbers just don’t work out under any reasonable scenario. Let’s make some assumptions:

You’d get 28 MPG on the highway with an E320 gas.

You’d get 35 MPG with an E300 diesel.

You pay $3.15 for a gallon for premium unleaded gasoline.

You pay $2.90 for a gallon for diesel. (Diesel is actually more expensive than premium gas in some parts of the country.)

Under these assumptions, gas for the E320 would cost $0.11 per mile and diesel for the E300 would cost $0.08 per mile. The diesel would reduce your fuel costs by about 3 cents per mile. To simply break even after paying the $5,000 premium for the diesel engine, you’d need to drive the car about 150,000 miles. Assuming you drive 10,000 miles per year, that would take 15 years!

The only factor that could significantly change would be that diesel fuel becomes much cheaper than gasoline in the future. If gas prices go up, or you convert your diesel to run on waste vegetable oil, then buying an E300 for fuel economy might make sense.

Other Ways to Save Money with a Diesel

Better fuel economy alone won’t make the diesel a good buy. But consider that the diesel engine may outlast the gasoline engines — although the odds of you having a major engine problem with a Mercedes gasoline engine are very low. The diesel would probably cost less to maintain. For example, diesels have no spark plugs, coils, ignition wires, etc., and therefore do not need traditional tune-ups. When you combine the fuel savings and potential maintenance/repair savings, the diesel could save you money if you plan to drive the car forever. If this is your plan, make sure you check your car thoroughly for rust before you buy! Otherwise, spend your extra $5,000 on a low mileage, museum-quality gasoline model.

Should I buy the diesel?

The diesel probably won’t be any cheaper to own unless you get a really, really good deal. So if you buy a diesel W210, you should buy it because you like diesels, not because you plan to save money. If you do your own maintenance, diesels are much simpler and easier to work on. As I mentioned before, diesels are enjoyable to drive. Some people (aka gearheads) like the unique diesel clatter, although you won’t hear any of it in the W210.

The Auto Channel: 1998 Mercedes-Benz E300 Turbodiesel Test Drive