Cummins' New 6.7 Diesel Engine Drops The Grid Heater, But Not Everyone Is Happy

At the start of 2025, Cummins unveiled its updated lineup of heavy-duty (HD) trucks under the Ram 2500 and Ram 3500 badges. Like the smaller Ram 1500, the larger HD models received a comprehensive refresh, featuring updated exterior styling, revamped interiors, new technology, and significant powertrain upgrades.

A standout change in the 2025 Ram HD lineup is the evolution of the 6.7L Cummins turbo diesel engine, a workhorse that has powered Ram trucks since 2007. For 2025, the engine undergoes several key enhancements, including a slight bump in horsepower — from 420 hp to 430 hp — while maintaining 1,075 lb-ft of torque. Additionally, it is now paired with an all-new TorqueFlite HD eight-speed automatic transmission, replacing the previous six-speed unit.

A major highlight for Ram 2500 buyers is the long-awaited arrival of the high-output (HO) version of the 6.7L Cummins. Previously exclusive to the Ram 3500, the HO variant now brings 430 hp and 1,075 lb-ft of torque to the 2500 series. This is a significant step up from the outgoing 2024 Ram 2500, which featured a lower-output version of the same engine with 370 hp and 850 lb-ft of torque, forcing buyers to upgrade to the Ram 3500 for maximum performance.

Aside from these noticeable performance gains, the updated Cummins 6.7L features several notable mechanical improvements, including a more reliable Bosch CP8 fuel pump, support for over-the-air software updates, and repositioned oil and dual fuel filters for easier maintenance.

While some Ram truck enthusiasts have welcomed these updates, one change has sparked debate — the switch from traditional grid heating technology to glow plugs. Some longtime owners are skeptical about the reliability and durability of this new approach, but Cummins insists the update will enhance cold-weather performance.

To begin with, both grid heaters and glow plugs are used in diesel engines to improve cold starting with extreme chill. They work by raising the temperature of the combustion chamber so that the engines reach an optimum temperature quickly. Since its inception, the Cummins 6.7L engine has used traditional grid heaters. These grid heaters have worked well on most Cummins 6.7L engines over the years.

The primary reason for existing Ram truck owners to be worried about the use of glow plugs on the updated 2025 Cummins 6.7L engine is the fact that glow plug technology is claimed to be inherently more complex than traditional grid heaters. Glow plugs, by design, require the deployment of individual glow plugs on each cylinder of the engine (six in the case of the Cummins 6.7L). Any one of these glow plugs going bad may lead to ineffective heating.

Cummins asserts that glow plugs are more efficient at heating the combustion chamber compared to grid heaters, ensuring faster cold starts. In contrast, those in favor of grid heaters argue that it is a tried and tested technology that Cummins has been using on the 6.7L engine for several years. Essentially, why fix something that isn't broken?

While there is no denying that Cummins' diesel engines are known for their reliability and longevity, it's not like they have been entirely free of issues. For example, the company's 5.9L diesel engines made between 1989 and 2002 were notorious for the infamous killer dowel pin issue. Cummins' 6.7L engine also suffered from a similar issue — specifically concerning the engine's grid heater unit.

Known as the infamous "grid heater problem," in the case of the Cummins 6.7L engine, this issue centers around a potential failure of the grid heater's hardware, specifically the bolts that secure it. As outlined earlier, the grid heater is designed to preheat the incoming air before it enters the engine's cylinders, especially during cold weather.

On some Cummins 6.7L engines, the bolts holding the grid heater in place can, over time, loosen, break, or melt due to the repeated cycles of heating and cooling, along with engine vibrations. Unfortunately, the positioning of this bolt is such that when it breaks, there is a high chance of its fragments falling into the engine's cylinders. There have been instances of these broken bolts causing catastrophic engine damage.

While this is a widely known issue, those still in favor of grid heaters assert that this issue is more of a Cummins design flaw than something fundamentally wrong with grid-heating technology.

Nevertheless, with the 2025 announcement of the updated Cummins 6.7L engine with glow plugs, the infamous grid heater problem should be a thing of the past. Only time will tell if the all-new glow plugs end up opening up a Pandora's box of entirely new issues.