The Diesel Buyers' Guide
The current popularity of multi-purpose and crossover vehicles notwithstanding, Diesel-powered vehicles should really be separated into two categories: trucks and passenger cars. Why?
Trucks, which are often used as tow vehicles, must be able to pull heavy loads, must provide lots of torque, ideally from idle on, and have to last for many hundreds of thousands of miles. Rock, rattle and roll, all night long!
Passenger cars, however, must provide an elevated level of comfort and need enough ooopmh to be able to pass other vehicles quickly. Passenger car engines are designed differently than truck engines, even Diesels.
The 'perfect' truck engine, even downsized, would be awful in a passenger car, and the perfect passenger car engine wouldn't be able to work well in even a half-ton pickup.
As so many things in life, engines are compromises. Simplified, in a truck, we compromise the higher sound level for increased longevity; in a passenger car we compromise longevity for higher comfort.
Grades: A (excellent), B (very good), C (satisfactory), D (acceptable), F (failed).
| CARS |
| MAKE & MODEL |
APPLICATION |
VERDICT |
| Mercedes 240D |
2.4-liter 4-cylinder, installed in the W115 body from 1973 until 1976, then in the W123 body until 1985. |
Fantastic engine, with 4 pots of 600cc each. Will last up to 250K miles before it starts smoking and gets weaker.
Very affordably priced spares readily available, new as well as used. A wonderful, super safe, super reliable car for a teenager, so my daughter got one.
A . . . for durability, C- . . . for power. Take your pick. |
| Mercedes 300D |
3.0-liter 5-cylinder, installed in the W115 body in 1975 and '76, then in the W123 body until 1985.
The 300D /8 is a very desirable car for life. |
Basically a 240D with one added cylinder (0.6 x 4 = 2,4; 0.6 x 5 =3.0). Smoother, a bit more powerful, but a tiny bit thurstier. 80 horses. As good as a 240D. Some 240D buyers don't want a 300D; some 300D buyers don't want a 240D. Frankly, the differences
A . . . for durability, C . . . for power. |
| Mercedes 300D, 300CD, 300TD Turbodiesel |
The D is the 4-door sedan, the CD a 2-door Coupe, the TD a 4-door wagon. T stands for transport, not turbo, by the way.
Installed in the W123 body from 1982 until 1985. Engine is the stock 5-cylinder 300D with a turbocharger, which added 50% more horsepower for a total of 120. |
The added power puts the turbocharged 300D in a complete new league. Arguably THE Mercedes to have, if you want to keep up with high speed traffic. The 300CD is already a collectors' car, and the 300TD has a enthusiastic following as well. Both cars are very hard to find in good condition and with reasonable mileage these days. Yes, they'll run over 200K without problems, but I wouldn't want to start out with one that has the kind of mileage already. Look for a clean car with a notch over 100K miles.
300D = B. 300CD and 300TD = A |
| Mercedes 300D Turbo, 300TD |
Successor of the W123, the W124 came with a turbocharged 3.0-liter 6-cylinder Diesel in 1986 and 1987. Cast iron block, aluminum cylinder head. 148 horsepower. |
More refined than the W123, the W124 is also a bit more complex and more plasticized than its predecessor. The '86 & '87 Diesels are the most powerful ones, but sadly there were quite a few problems due to different expansion rates of block and head. Make sure you get a well-taken-care of car with documented service history. If you're looking for a wagon, this is an attractive candidate.
300D sedan = B-; 300TD wagon = A- |
| # 1 |
# 2 |
# 3 |
| TRUCKS |
| MAKE & MODEL |
APPLICATION |
VERDICT |
Chevy/GM/Oldsmobile
5.7-liter |
Installed in late '70s/early '80s GM vehicles |
Hastily "converted" from GM's 350 gas engine, these early Diesels were extremely trouble prone and cracked heads and thin-walled engine blocks like walnut shells.
F . . . stay away! |
Chevy/GM
6.2-liter |
Installed in pickups, Blazers, Suburbans, and the early H1 Hummers. |
Not a great engine by any stretch of the imagination. Not really trouble prone (aside from some overheating issues), but rather gutless.
D . . . why bother? |
Chevy/GM
6.5-liter Turbodiesel |
Successor of the 6.2, much better, more power. THE engine that powered the Hummer H1 until the second-to-last year of production. |
Despite what people have heard and may think, this is not a bad engine. Wouldn't be my first choice, or second, but I wouldn't be afraid of owning one.
C |
GM Duramax
made by Isuzu |
The General's new generation of Diesel engines, installed in pickups, the last year Hummer H1, and, sadly, until this day in not many other vehicles. |
Very lightweight and compact. Fine engine.
B+ |
Keep in mind that all of the above grades are subjective. Put a Chevy and a Ford lover in one room and have them figure out which one is the better car and you'll end up with a hung jury, as sure as there's death and taxes. So, please, take everything you read here with a grain of salt and remember that there are many shades or gray between white and black.
To be continued . . .
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