Just received in the mail today a nice letter from Mercedes-Benz USA, all done up on Very Nice stationary, thanking me for “choosing one of the most advanced diesel automobiles in the world…” and then just about screaming at me to stick to the factory maintenance schedule.

It is critical that you follow the service interval requirements of not more then 10,000 miles or one (1) year, whichever comes first.   Permanent engine damage can occur if the interval is not closely followed.

(Emphasis theirs!)   Followed by two more pages of Very Nice stationary detailing the maintenance schedule. As if I’d buy a car this expensive and not read the service book.   You best believe I read the service book.   Like a seminarian studying the holy writ I read the service book.

But I get their concern.   I don’t think American drivers understand diesels.   I wonder sometimes if one reason the Germans don’t import many of their diesel models into this country is because most American drivers just don’t know how to take care of one.   The reputation of diesels, particularly Mercedes diesels, for über longevity probably doesn’t help any.   People think hey…it’s a diesel…they’re tough. Well…yes.   They’ll outlast a gasoline burner every time.   But you have to do the maintenance.   Oh…and don’t stomp on the accelerator in a futile attempt to get gasoline engine acceleration out of one because it isn’t in there.

The simplest routine thing you do for a car’s engine, the oil change, is absolutely vital for a diesel engine.   That’s because the compression ratios on a diesel are greatly higher then even a high performance sports car’s is.   Compression is how a diesel ignites its fuel. They work on the principle that compressing air heats it up.   So at operating temperature a diesel gulps down a bunch of air, compresses it to temperature, and then at the right moment injectors squirt in the fuel and it ignites and you get your power stroke.   For that to work compression has to be high enough to heat the air enough. (when starting cold, diesels use either glow plugs or pre-heat the fuel before it is injected.)

Compare: The Corvette LS9 6.2 liter V-8 with an Eaton four-lobe Roots type supercharger has a power output of 638 bhp at 6500 rpm and 604 lb ·ft at 3800 rpm and a compression ratio of 9.1:1.   My 3 liter V-6 twin turbocharged Mercedes diesel on the other hand has a compression ratio of 17:1.   In diesel fashion it only generates 240 bhp at a red line of 4500 rpm…about a third the Vette’s.   However it generates 400 lb ·ft at 1800 rpm.   So the Vette engine has it on torque and horsepower, but the diesel is less then half its displacement, still has 2/3rds its torque and look at where the torque Is.

These engines are not racehorses, they’re draft horses and they will go any distance and bear loads that would give a gasoline burner of equal size a heart attack.   But you absolutely have to do the maintenance.   You can slack on the oil changes in a gasoline burner or cheap out on the grade of oil used and still get good service out of one for quite a while before it catches up with you and gets expensive.   A diesel can be completely destroyed in a very, Very short time if you do that.   Like in under 30k.   Try this wee experiment: look at the dipstick right after you’ve given a diesel engine an oil change.   See how nice and golden the oil is?   Look at it again at 100 miles.   Looks dirty as hell doesn’t it?   17:1 and running on diesel oil not lightweight gasoline will do that.

This is the big reason why I never bought one second hand though I’ve wanted one since I was a teenager.   By the time I was old enough and making enough to afford a second hand Mercedes diesel I’d seen tragically what your typical American driver does to a diesel engine.   Yes, they’ll last practically forever.   You can’t build 17:1 ignition-by-compression on the cheap and expect it to outlast the warranty.   And the routine maintenance isn’t expensive.   But you have to do it.

And I would recommend changing the oil twice as often as the factory recommends on any car.   I’ve done that on every car I’ve ever owned and never had any engine problems.   But it’s especially critical for a diesel.   Daimler gives its engines very large oil reservoirs…something around nine quarts in the V-6s (compared to around 6 in an American V-8) and they say change every 10k.   I change at five.   The other service gets done on schedule.

So anyway…I’m looking at this very nice letter from Mercedes-Benz USA printed on Very Nice stationary and what I’m seeing is evidence that Americans just don’t know how to take care of a diesel.   And these aren’t just any diesels.   These are Mercedes-Benz.   These are magnificent automobiles, they are expensive, they are exceptionally well made, and it is so embarrassing to see how MBUSA needs to gently remind its customers…it’s presumably well to do customers…on Very Nice stationary, to take fucking care of their cars.