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Diesel Engine Pros and Cons

Reasons for buying, or passing on a diesel powerplant in a new truck.

Sep 16, 2020
Photographers: trucktrend
We recently noted that although many of us like to think we're without error at all times, nothing in our world is 100 percent fail proof. There's a small margin for error in everything. The important thing is we should never allow that window to open too wide.
The concept certainly applies to diesel truck engines. While "oil burners" (as the powerplants are endearingly called) have many benefits, there also are some negative aspects to diesel.
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With this report, we're taking a look at those pros and cons, offering our insights based on today's Ford, GM, and Ram fullsize rigs. When it's all said and done, there are very few, well, only one major con about diesel engines. So, no, they're not perfect, but that one drawback definitely is not big enough to rule out buying a pickup that's powered by oil.
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* Fuel Economy: With prices now rivaling those of gasoline in some areas (Southern California is a prime example), diesel's cost is definitely many owners' biggest concern. One of the biggest plusses about diesel is that its energy density is greater than that of gas, by nearly 22,000 BTU. Basically, a port-injected gasser will burn much more fuel in order to match a direct-injected diesel's power output—per gallon—unloaded and especially when towing. Unfortunately, the U.S. Environmental Protection Agency doesn't publish fuel economy data for heavy-duty, fullsize trucks. But, based our Pickup Truck of the Year and other evaluations, diesel-powered Ford F-250 and F-350 (6.7L Power Stroke), and GM's (6.6L Duramax L5P) and Ram's (6.7L Cummins) 2500 and 3500 Series rigs demonstrate better efficiency by roughly 8 mpg over their gas-motivated siblings. At the heavy-duty level, the big score with diesel ultimately is economic. Over time and after many refuelings, the win over gas becomes quite apparent.
* Performance, Reliability, and Longevity: Today's diesel engines are highlighted by torque output of 910, 1,000, and 1,050 lb-ft that gives trucks ability to tow more than 35,000 pounds and carry payloads of more than 6,300 pounds. The total length of their service term is all about maintenance and upkeep, but they typically run for up to 350,000 miles without demonstrating abnormal signs of deteriorating. Gas engines have much smaller horsepower and torque numbers and, despite solid maintenance, shorter life expectancy. Oil service as prescribed by the manufacturer, along with air-, and fuel-filter changes, are critical to an oil-burner's tour of duty.
* Flexibility: Although they are not included in the formal/"Flex-Fuel" family of versatile engines, diesels are capable of operating with biodiesel in a truck's fuel tank.
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* Cost: The biggest immediate negative about a modern diesel engine is price—for the optional powertrain itself (the 6.6L Duramax L5P in a recently tested 2020 Chevrolet Silverado 3500HD adds $9,890 to the $36,500 base cost), and also for ultra-low sulfur fuel that must be used. Fuel stations' actual locations often have a lot to do with price, too. In some areas, you simply can't find diesel, because there's no demand. Currently, diesel fuel actually costs more than premium-grade gasoline in some areas of the U.S. (in SoCal, plan on paying $3.00/gallon on average, or more). And, since the late 1990s, diesel exhaust fluid (DEF) is part of the expense mix. The fluid must be refilled regularly and particulate filters serviced as necessary.
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