Modern Tech
The True Cost of Diesel
By Ken Adams
Occasionally I am asked which are better from an economic standpoint – gasoline or diesel engines. At first glance at the EPA mileage ratings on the window stickers of the Mercedes models that offer both engines, the clear winner looks like the diesel.
However, before you run out and buy a diesel, there are a few aspects of the diesel system compared with a gasoline system of which you should be aware.
In the past, diesels were perceived to be slow, smelly and noisy. I am happy to say that has changed, thanks to improved diesel emission and fuel-management controls. If you remember a few years back, few 6-cylinder diesel engines could meet California emission standards, the most stringent standards for automobile exhaust emissions in North America. The answer to this problem from Mercedes-Benz was a family of new diesel technologies called “BlueTEC.”
BlueTEC is a trade name Mercedes Benz adopted to promote its new generation of clean-burning 6-cylinder diesel engines. These engines are equipped with an array of advanced technologies, including high-pressure fuel injection, variable-vane turbocharging, and sophisticated electronic sensors and controls. One of the key elements in these technologies is a liquid known generically as diesel exhaust fluid (DEF) and also by the trade name AdBlue. AdBlue is trademarked by the German Association of the Automobile Industry that has established quality standards for the product sold by dealers of German automobiles under that name.
DEF, or AdBlue, is an aqueous urea solution blended of 32.5 percent high-purity urea and 67.5 percent deionized water. In Mercedes-Benz diesel automobiles, there is a small tank holding approximately 7.5 gallons of AdBlue under the trunk or cargo area in the rear of the vehicle. The fluid is injected into the exhaust system upstream of the selective catalytic reduction (SCR) catalyst and reacts within the catalyst to convert nitrous-oxide emissions into harmless nitrogen and oxygen. A full tank of AdBlue should last about 10,000 miles.
An important point to note about the AdBlue diesel system is that the system is designed in accordance with EPA standards not to operate without AdBlue. When the fluid level drops to the point where it calculates there are only 600 miles to go before the AdBlue tank is empty, drivers will start to receive a message on the instrument cluster stating there are only 20 starts remaining; the system will count down from there. If all 20 starts are used before refilling the Adblue tank, you’re done. The engine will not start.
In response to another question that is often asked, some manufacturers have 4-cylinder diesel engines on their smaller automobiles that do not require the AdBlue system. The exhaust emissions on these lower-power cars can be handled entirely by a filter in the exhaust system that traps the emissions as ash, which is periodically burned off in normal operation.
A dealer can fill the AdBlue tank at the normal service interval when you have the vehicle in for its oil change and maintenance. If you’re the kind of person who changes your own oil and sees to your own service, you can purchase the necessary DEF in convenient 2.5-gallon bottles with special filler necks from most full-line automotive parts stores. Prices vary from $10 to $20 per bottle, or $30 to $60 per fill-up. Refilling the tank is no more complicated than filling your windshield washer fluid. The typical cost for the full 7.5-gallon fill-up at the dealer will be approximately $170, in addition to the regular servicing charges, although the fluid cost may vary from dealer to dealer.
There are two other additional operating costs associated with the diesel-powered vehicles. In the diesel-powered ML-, GL-, and R-Class vehicles, the AdBlue tank takes up the space allotted for the spare tire in gasoline-powered vehicles. With no room for a spare tire, these vehicles are equipped with run-flat tires that cost approximately twice the cost of standard tires. In addition, the diesel service requires replacing the fuel filter every 20,000 miles.
So, how do the costs compare? For this analysis, I used the 2012 model ML350 and ML350 BlueTEC, and assumed the vehicles were driven through three full service intervals, or 30,000 miles.
Comparative Costs of Gasoline and Diesel
ML350 ML350 BlueTEC
Combined fuel mileage 19 mpg 22 mpg
Gallons of fuel 1,579 1,363
Cost of fuel per gallon $3.75 $4.00
Total cost of fuel $5,92 $5,454
AdBlue 22.5 + labor 0 $510
Replacing tires $1,200 $2,400
Diesel fuel filter 0 $182
Total Costs $7,121 $8,546
As you can see, the extra costs associated with the BlueTEC diesel do cancel the mileage savings. However, because of the additional torque, many applications such as towing a trailer or driving on hilly terrain make the diesel a better choice, and the reduced fuel consumption makes it a better environmental choice. Compared to these advantages, the extra $1,425 over 30,000 miles – not quite a nickel a mile – may be inconsequential.
The True Cost of Diesel
By Ken Adams
Occasionally I am asked which are better from an economic standpoint – gasoline or diesel engines. At first glance at the EPA mileage ratings on the window stickers of the Mercedes models that offer both engines, the clear winner looks like the diesel.
However, before you run out and buy a diesel, there are a few aspects of the diesel system compared with a gasoline system of which you should be aware.
In the past, diesels were perceived to be slow, smelly and noisy. I am happy to say that has changed, thanks to improved diesel emission and fuel-management controls. If you remember a few years back, few 6-cylinder diesel engines could meet California emission standards, the most stringent standards for automobile exhaust emissions in North America. The answer to this problem from Mercedes-Benz was a family of new diesel technologies called “BlueTEC.”
BlueTEC is a trade name Mercedes Benz adopted to promote its new generation of clean-burning 6-cylinder diesel engines. These engines are equipped with an array of advanced technologies, including high-pressure fuel injection, variable-vane turbocharging, and sophisticated electronic sensors and controls. One of the key elements in these technologies is a liquid known generically as diesel exhaust fluid (DEF) and also by the trade name AdBlue. AdBlue is trademarked by the German Association of the Automobile Industry that has established quality standards for the product sold by dealers of German automobiles under that name.
DEF, or AdBlue, is an aqueous urea solution blended of 32.5 percent high-purity urea and 67.5 percent deionized water. In Mercedes-Benz diesel automobiles, there is a small tank holding approximately 7.5 gallons of AdBlue under the trunk or cargo area in the rear of the vehicle. The fluid is injected into the exhaust system upstream of the selective catalytic reduction (SCR) catalyst and reacts within the catalyst to convert nitrous-oxide emissions into harmless nitrogen and oxygen. A full tank of AdBlue should last about 10,000 miles.
An important point to note about the AdBlue diesel system is that the system is designed in accordance with EPA standards not to operate without AdBlue. When the fluid level drops to the point where it calculates there are only 600 miles to go before the AdBlue tank is empty, drivers will start to receive a message on the instrument cluster stating there are only 20 starts remaining; the system will count down from there. If all 20 starts are used before refilling the Adblue tank, you’re done. The engine will not start.
In response to another question that is often asked, some manufacturers have 4-cylinder diesel engines on their smaller automobiles that do not require the AdBlue system. The exhaust emissions on these lower-power cars can be handled entirely by a filter in the exhaust system that traps the emissions as ash, which is periodically burned off in normal operation.
A dealer can fill the AdBlue tank at the normal service interval when you have the vehicle in for its oil change and maintenance. If you’re the kind of person who changes your own oil and sees to your own service, you can purchase the necessary DEF in convenient 2.5-gallon bottles with special filler necks from most full-line automotive parts stores. Prices vary from $10 to $20 per bottle, or $30 to $60 per fill-up. Refilling the tank is no more complicated than filling your windshield washer fluid. The typical cost for the full 7.5-gallon fill-up at the dealer will be approximately $170, in addition to the regular servicing charges, although the fluid cost may vary from dealer to dealer.
There are two other additional operating costs associated with the diesel-powered vehicles. In the diesel-powered ML-, GL-, and R-Class vehicles, the AdBlue tank takes up the space allotted for the spare tire in gasoline-powered vehicles. With no room for a spare tire, these vehicles are equipped with run-flat tires that cost approximately twice the cost of standard tires. In addition, the diesel service requires replacing the fuel filter every 20,000 miles.
So, how do the costs compare? For this analysis, I used the 2012 model ML350 and ML350 BlueTEC, and assumed the vehicles were driven through three full service intervals, or 30,000 miles.
Comparative Costs of Gasoline and Diesel
ML350 ML350 BlueTEC
Combined fuel mileage 19 mpg 22 mpg
Gallons of fuel 1,579 1,363
Cost of fuel per gallon $3.75 $4.00
Total cost of fuel $5,92 $5,454
AdBlue 22.5 + labor 0 $510
Replacing tires $1,200 $2,400
Diesel fuel filter 0 $182
Total Costs $7,121 $8,546
As you can see, the extra costs associated with the BlueTEC diesel do cancel the mileage savings. However, because of the additional torque, many applications such as towing a trailer or driving on hilly terrain make the diesel a better choice, and the reduced fuel consumption makes it a better environmental choice. Compared to these advantages, the extra $1,425 over 30,000 miles – not quite a nickel a mile – may be inconsequential.