Mercedes-Benz dealers heavily marking up service products? You don't say.

Drivers of Benz's turbodiesel-powered ML350 BlueTEC 4Matic are obliged to periodically refill the vehicle's supply of diesel emissions fluid, which is made up of urea crystals in mineralized water and which is required to turn some of the SUV's exhaust from nitrogen oxides to nitrogen and water, according to The New York Times. Once those fluids run out, the SUV shuts down.

With that prospect in mind, some dealers are charging as much as $32 for a gallon for the fluid that's good for about 1,500 miles, according to the Times. So, with the SUV getting a combined 22 miles per gallon, that equates to an additional 47 cents for each gallon of diesel used. Most Benz buyers won't lose sleep over that, but it certainly offsets much of the $450 a year the EPA says diesel buyers save in refueling costs relative to the gas-powered version of the SUV.

The good news, according to the newspaper, is that stores such as Napa Auto Parts and AutoZone sell jugs of the fluid for about $5.20 a gallon, though a Mercedes-Benz spokeswoman said D.I.Y.-ers lose out on the dealers' flushing out of the system and risk the fluid crystallizing if it sits for two long. Whether that's worth the sixfold mark-up depends on the driver and his or her income-tax bracket.