The diesel ram engine that defies time and kilometers

Dodge RAMs have a well-documented history of bulletproof engines, and if you’re lugging around a heavy-duty pickup, this is one of the most useful assets you can have. An engine with enough torque to tow a small house, and reliable enough to outlast the truck itself. Even in modern times, RAMs are considered very rugged vehicles. The RAM1500 from 2024 received a quality and reliability rating of 89/100, proving that the legacy lives on, with much more complex engines.

One of the indestructible powertrains that really showed the world its longevity was the 5.9-liter inline-six. And although production in RAMs lasted 18 years (1989 to 2007) and saw several changes during that time, the intention and the result were always the same. An engine that can do everything and do it forever. Truly a legend from the past that defies time and mileage, and with plenty of examples still functioning as workhorses today, this is more true than ever.

What makes this engine so indestructible?

The key to the reliability of this engine depends on a few important factors, from which we are increasingly distant in modern times. Starting out as a powertrain intended for industrial equipment such as tractors, this meant it was designed to pull extremely heavy vehicles. Not only did this make the engine over-engineered in the first place with an abundance of cast iron and massively strong components, but putting it in a pickup would mean the engine was severely under-stressed compared to its original use.

Despite being cast iron, most powertrains still suffer from the usual problems that undermine a diesel’s long-term power. Firstly, modern chains and timing belts always require replacement over time and are always a risk factor, even if proper maintenance is carried out. The 5.9-liter inline-six was driven by gears, a heavy-duty solution compared to alternatives that snap or stretch. Not only that, but the connecting rods and bearings used were massive compared to gasoline car or even standard truck engines, making it easy to maintain consistently high torque pressure.

Changes over the years to the drivetrain

The engine was first used in a Dodge RAM in 1989, and this version of the powertrain remained similar until 1998. In 1994 they introduced the Bosch P7100 inline injection pump, which was insanely durable and marked the beginning of the truly bulletproof era. In the four years leading up to 1998 it was seen as a true masterpiece. With the upgrade allowing easy tuneability and massive horsepower, and durability still intact, this was truly the golden age for the engine.

Core generations of the 5.9-liter inline-six

• 1989-1998 More mechanical engine with 12 valves

• 1998-2002 ISB with 24 values ​​and electric refueling

• 2003-2007 shift to 24-valve common rail

• Turbo update from 2004-2007 for 610 Ib-ft of torque

Each of these iterations kept the basic principles in place, but they all had their own quirks. The first generation was incredibly simple and the most reliable, but lacked some of the enormous torque produced later. The 1998-2002 model had the most problems due to the new electronic weaknesses and the infamous VP44 pump; some were known to leak coolant. By the time the run came to an end, however, they had solved most of the problems: better injectors and a superior high-pressure pump. This gave the 5.9-liter a powerful final farewell with excellent torque figures and legendary reliability.

How this engine made the RAM a legend

Since Ford and Chevrolet were by far the most popular pickups in the 1980s, Dodge had a lot of work to do. The 5.9-liter Cummins was more than a spectacular engine; it made the truck itself a force to be reckoned with. It became impossible to ignore. When people became aware that Dodge was switching to a 5.9-liter diesel engine from Cummins, it surprised people and gave it connotations of serious power. And while gasoline was the gold standard for trucks at the time, the 1989 Dodge RAM proved it could haul loads that Ford struggled with at an effortless 1,700 rpm. This was the last generation of the 5.9-litre Cummins engine in the RAM and allowed for extremely impressive specs and a huge increase in torque whilst retaining power.

2005-2007 Dodge RAM 5.9-liter Cummins specs

The shift from the 5.9-liter Cummins to the 6.7-liter Monster

A more modern engine would replace the 5.9 Cummins, a beast in itself. The 6.7-liter engine that would bring the RAM engines to the fore in 2007 would still offer incredible reliability, with examples traveling more than 500,000 miles. While that may not be as shocking as the 5.9-liter’s praise for being part of the “Million Mile Club,” half a million miles still points toward an incredibly designed engine. The 6.7-liter Cummins has a lot in common with the 5.9-liter outgoing variant. Fortunately, the 6.7 used many of the same high-quality components as the 5.9, with the cast iron heart still being the epicenter of its capabilities.

The inline-six remained almost exactly the same in layout, meaning it would continue the trend of the natural balance and lack of heavy vibration as the previous engine. After the 5.9-liter learned its lesson by using an extremely durable injection pump, the 6.7-liter continued this trend and stuck with the rock-solid Bosche CP3 pump. What ultimately killed the 5.9-liter in the Dodge were the poor emissions. It simply wasn’t suited to the early move towards green measures in the mid-2000s, so they added an EGR and DPF filter to vastly improve emissions. While these filters have been known to clog and cause reliability issues, it was necessary to keep large diesel engines on the road.

The verdict on the legendary 5.9-liter Cummins

The excellent 5.9-liter inline-six Cummins was more than just a cool engine; it redefined what a pickup could do. It wasn’t just a pretty powerful car with a tow bar and a bed in the back; it was something that could easily pull loads many times heavier than the truck itself, something that pushed the boundaries of what was possible. And for Dodge, it has put RAM on the map as the gold standard for heavy users.

With RAM continuing to thrive in recent years, even with a shift to hybrid engines and a move away from diesel, it’s essential to remember that much of this success was down to that phenomenal and unstoppable, truly bulletproof cast-iron inline-six. And while emissions simply don’t allow such engines to be produced now, we can still expect to see plenty of 5.9-liter RAMs on the roads in the coming decades.

Sources: RAM, Dodge, JD power