Why The Cummins 6BT Is Considered The Best Diesel Engine Ever Made

It's not uncommon to hear of old technology becoming fan favorites among the automotive community. As an example, one need only look at the cult following that the Toyota Hilux has generated thanks to its reliability and reputation for taking a beating. The Cummins 6BT is much of the same story. While its power and torque output were excellent at the time, they haven't held up as well, but the 6BT has earned a reputation largely due to its reliability, despite having been replaced by the much larger and more powerful Cummins 6.7 L ISBe engine. 

According to Chrysler press releases from the Detroit Public Library's National Auto Historic Collection (transcribed and published online on Allpar.com) that detail why Dodge decided to use the 6BT, the carmaker used the Cummins 6BT motor in the Ram pickup truck between 1989 and 1998 to compete with increasing demands for low-down torque for heavy-duty applications. But over the years, the motor has also been used in everything from buses to marine applications and generators thanks to its reputation for being virtually immortal. 

According to Cummins, the 6BT was a 5.9-liter, inline-six, water-cooled, and turbocharged four-stroke diesel engine that produced between 160 and 215 horsepower and between 400 and 440 lb-ft of torque. The 6BT featured two overhead valves per cylinder, for a total of twelve, and was fed by a Bosch direct fuel injection system. Looking online, you'll see folks putting the 6BT engine in just about anything that needs an engine, all in the name of reliability. 

The Cummins 6BT is a simple engine with reasonable performance. According to the Chrysler press release on Allpar.com, the 6BT was chosen for the medium-duty truck because of its simplicity and torque — Not only was an inline-six engine easier to work on than the V-configurations it competed against, but it also had 40% fewer parts at the time. According to Dust Runners Automotive Journal, the BT6 featured a cast-iron cylinder head and engine block, which made it incredibly tough but sacrificed in the weight department. The all-mechanical direct fuel-injection system made it both easy to repair and work on, although some common problems with the 6BT are related to the fuel system, according to Diesel IQ. 

Featuring a compression ratio of about 17:1 — low, considering some diesel motors run at up to 25:1, according to E-ZOIL – the 6BT is comparatively under-stressed, adding to its longevity. The combination of performance, ease of maintenance, and durability make the Cummins 6BT a fan favorite.