At the beginning of 2025, Cummins introduced its refreshed heavy-duty (HD) truck lineup under the Ram 2500 and Ram 3500 names. Like the smaller Ram 1500, these larger HD models have been thoroughly updated with new exterior designs, enhanced interiors, innovative technology, and substantial powertrain upgrades.
Advertisement
One prominent change for the 2025 Ram HD lineup is the update to the 6.7L Cummins turbo diesel engine, which has been the backbone of Ram trucks since 2007. This year, the engine receives several significant updates, including a minor increase in horsepower from 420 hp to 430 hp while retaining a torque of 1,075 lb-ft. Additionally, it now comes with an all-new TorqueFlite HD eight-speed automatic transmission, replacing the previous six-speed version.
For Ram 2500 buyers, a key aspect is the long-awaited introduction of the high-output (HO) variant of the 6.7L Cummins engine. Previously only available in the Ram 3500, the HO variant now offers 430 hp and 1,075 lb-ft of torque in the 2500 series—an upgrade from the outgoing 2024 Ram 2500 that had a lower-output version with 370 hp and 850 lb-ft of torque, making it necessary for buyers to opt for the Ram 3500 for peak performance.
Advertisement
Beyond these visible performance enhancements, the revised Cummins 6.7L engine brings several notable improvements, such as a more dependable Bosch CP8 fuel pump, support for over-the-air software updates, and repositioned oil and dual fuel filters for streamlined maintenance.
Though many Ram truck enthusiasts have praised these updates, one revision has sparked controversy—the transition from traditional grid heaters to glow plugs. Some long-time owners are doubtful regarding the reliability and durability of this new technology, but Cummins asserts that the change will improve cold-weather operation.
Simple grid heaters vs. complicated glow plugs
Initially, both grid heaters and glow plugs are utilized in diesel engines to aid cold starts in extreme conditions. They function by increasing the temperature of the combustion chamber, allowing engines to reach optimal temperatures quickly. The Cummins 6.7L engine has historically employed traditional grid heaters, which have performed reliably over time.
Advertisement
The primary concern for existing Ram truck owners regarding the switch to glow plugs in the updated 2025 6.7L engine is the notion that glow plug technology is typically more complex than the simpler grid heaters. Glow plugs must be deployed individually for every cylinder in the engine (six for the Cummins 6.7L). Hence, if any single glow plug fails, it may lead to inadequate heating.
Cummins claims that glow plugs provide greater efficiency in heating the combustion chamber compared to grid heaters, ensuring quicker cold starts. Conversely, proponents of grid heaters defend their reliability, asserting that they are time-tested technology effectively utilized by Cummins for many years. Essentially, the question remains—why change something that has consistently worked?
Advertisement
Grid heaters haven’t entirely been free of trouble
Although Cummins diesel engines are acknowledged for their reliability and durability, they have not been completely without issues. For instance, the 5.9L diesel engines manufactured between 1989 and 2002 were infamous for the killer dowel pin issue. Similarly, the 6.7L engine faced challenges related to its grid heater system.
Advertisement
Referred to as the infamous “grid heater problem,” this situation pertains to the potential malfunction of the hardware securing the grid heater, specifically the bolts. The grid heater’s purpose is to preheat incoming air prior to its entry into the engine’s cylinders, especially in cold weather.
In certain Cummins 6.7L engines, the bolts securing the grid heater might loosen, break, or melt over time due to the repetitive heating and cooling cycles, combined with engine vibrations. This particular positioning means that when a bolt fails, fragments are likely to fall into the engine’s cylinders, leading to serious engine damage in some cases.
Advertisement
While this problem is well-documented, supporters of grid heaters argue that it stems from a design flaw in Cummins rather than being a fundamental flaw with grid-heating technology itself.
Nevertheless, with the announcement of the updated 2025 Cummins 6.7L engine equipped with glow plugs, it appears that the notorious grid heater problem may become a relic of the past. Only time will determine if the new glow plugs might introduce a completely different set of issues.
