Torture Test Demonstrates How a Cummins Diesel Endures Cold Starts as Low as -40 Degrees

      **Banks Power**

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      Diesel engines struggle in cold conditions. Low temperatures cause fluids to thicken significantly, while simultaneously draining power from a truck’s batteries, presenting substantial challenges for your vehicle during winter. While modern pickups have improved in handling cold starts, there are still limits, which is why this cold chamber in Southern California was specially designed to test those boundaries. Banks Power froze a Cummins diesel Ram to evaluate its performance at -40 degrees.

      The experiment utilized a 2024 Ram 2500 HD in optimal condition. Banks installed new Interstate AGM batteries and replaced the 6.7-liter engine’s fluids with fresh Amsoil products, including the Signature Series 5W-40 oil. They also used winter diesel combined with an Amsoil additive to prevent gelling, and to ensure proper performance, they replaced the fuel-water separator before testing.

      That took place at the Thermal Dynamics lab in Southern California.

      Turbodiesel pioneer Gale Banks initiated the test by identifying four critical factors affecting diesel engine start procedures: ambient temperature, coolant temperature, heat of compression, and manifold air temperature. While some factors are beyond control, block heaters and intake air heaters can help improve coolant and manifold air temperatures.

      To demonstrate the significant impact of block heaters, Banks conducted tests with and without one. They measured coolant temperature, resting voltage, cranking voltage, and cranking RPM under various conditions, using a starting temperature of 75 degrees Fahrenheit as the ideal scenario. The findings were revealing:

      When tested without a block heater at -20 degrees Fahrenheit, the coolant temperature matched the outside air, making starting the engine and reaching optimal operating temperature much more difficult. This was evident as the engine could only crank at 82 RPM during that test, reflecting a 46.9% reduction in piston speed, crucial for diesel engine ignition. This test utilized 1,500 watts of power to warm the intake air, provided by a dual-element Banks Power Monster Ram.

      The bottom chart shows that with a block heater, the coolant temperature rose to 32 degrees Fahrenheit, despite the same -20 degree ambient temperature. This significantly reduces engine wear, as internal cylinder temperatures can exceed 300 degrees upon startup. A warmer coolant in the water jacket surrounding the cylinder minimizes the temperature difference, leading to better engine performance over time. It's important to note that piston speed still decreased by 38% compared to the warm weather start; however, the -20 degree test with the block heater was accompanied by only a single 750-watt intake air heater element.

      Two pre-heating cycles substantially improved manifold air temperature.

      Even at -30 degrees Fahrenheit, the block heater raised coolant temperature to 20 degrees. Under these conditions, the truck achieved 89 cranking RPM thanks to heat from a 1,500-watt, dual-element Monster Ram intake.

      As temperatures continued to drop, the truck completely failed to start at -40 degrees. With a cranking voltage of only 6.4 volts, the batteries were insufficient to keep the ECU operational. Naturally, the Monster Ram couldn’t assist, although the block heater maintained coolant temperatures at 9 degrees Fahrenheit.

      These tests highlight the importance of hardware. Block heaters should be standard for diesel truck owners in cold-weather regions, and heated intake air is evidently vital as well. Cummins installed factory grid heaters on pickups like the 2024 model used in this test, though many have experienced issues due to a faulty bolt that melts and contaminates the engine. This could explain Cummins’ switch to glow plugs in 2025, which is undeniably one of the key advantages of a Monster Ram intake, especially with their models now offering a triple-element design utilizing 2,250 watts.

      Have a tip or question for the author? Contact them directly at: caleb@thedrive.com