The diesel market has become increasingly competitive, and Cummins has continuously updated the 6.7L Turbodiesel to keep pace. Many of its modifications over time were driven by rising performance demands, which required structural reinforcements to withstand higher stresses. Other updates focused on cleaner emissions, better fuel efficiency, enhanced reliability, or a mix of these factors. The most extensive updates occurred in the 2013, 2019, and 2025 model years.

2009

• Added an access port in the turbocharger turbine housing, allowing VGT vane cleaning without removing the turbocharger for easier servicing.
• Upgraded fuel filter housing and filter element for improved filtration.
• Redesigned water pump inlet housing.
• Updated EGR coolant hoses and fittings.

2010

• Transitioned to a single PCM (engine-mounted ECU) managing both engine and transmission, replacing the previous dual-unit setup.
• Revised fuel filter housing with a quarter-turn drain valve.
• Updated thermostat with a higher 200 °F opening point, slightly raising operating temperature (not interchangeable with older versions).

2011

• Pickup models with the 68RFE automatic gained 150 lb-ft of torque, while horsepower stayed the same. G56 manual trucks saw no performance changes.
• Chassis cab models received SCR emissions aftertreatment, requiring DEF.

2013

• Across-the-board power increases: chassis cab G56 models +15 hp/+40 lb-ft, automatics +20 hp/+140 lb-ft, pickup G56 models +50 lb-ft (no hp increase). Standard output gained 20 hp but stayed at 800 lb-ft.
• A new High Output version debuted for Ram 3500s, adding +15 hp and +50 lb-ft over standard.
• SCR became standard for all pickups (DEF required).
• Mechanical updates included a new camshaft (chassis cabs), redesigned pistons, piston skirt coating, new cooling jets, new vibration damper, updated bedplate, Holset HE300VG turbo, larger EGR cooler, smaller water pump/fan pulley, and a new ECU with more processing capacity.
• AS69RC replaced AS68RC in chassis cabs.

2016

• H.O. engines recalibrated for +35 lb-ft, reaching 900 lb-ft. Standard and chassis cab engines unchanged.

2018

• H.O. torque increased to 930 lb-ft. No changes for standard output or chassis cab.
• Final year for the G56 manual transmission.

2019

• Pickup engines received torque boosts: H.O. from 930 to 1,000 lb-ft and standard output from 800 to 850 lb-ft. H.O. power rose from 385 to 400 hp, making the 6.7 Cummins the first pickup engine to hit 1,000 lb-ft. Chassis cab calibration unchanged.
• Significant redesigns included:
  • New pistons (larger wrist pins, revised bowl geometry, lower friction rings, altered compression ratios).
  • Stronger forged rods and crankshaft.
  • A compacted graphite iron (CGI) block for strength and weight reduction.
  • Updated cylinder head (new springs, valves, rocker arms, larger bolts).
  • Hollow camshaft, new hydraulic lifters, and revised rocker arms.
  • Updated Holset turbo delivering up to 33 psi boost.
  • New exhaust manifold design and turbo relocation.
  • Bosch CP4.2 pump (replacing CP3), raising injection pressure to 29,000 psi.
  • Revised injectors, cooling, lube oil pump, and aluminum housings for oil/water pumps.

2020

• Chassis cab calibration raised to 360 hp (+35) and 800 lb-ft (+50). Pickup engines unchanged.

2021

• Returned to Bosch CP3 pump after CP4 issues; recall issued for 2019–2020 models to retrofit CP3.
• H.O. engines gained +20 hp and +75 lb-ft with a new ECU calibration.
• Standard and chassis cab engines unchanged.

2025

• Ram streamlined the diesel lineup to a single option: the H.O. 6.7 Cummins paired with the ZF PowerLine 8-speed automatic. Pickup and chassis cab models share the same engine but retain different ECU calibrations, with pickups receiving an extra 10 hp.
• Major updates included:
  • Bosch CP8 fuel pump rated to 32,000 psi.
  • Traditional glow plugs replacing the grid heater for cleaner startups.
  • New cartridge-style oil filter.
  • Revised turbocharger.
  • Engine-mounted DOC for quicker light-off and better efficiency.
  • Updated EGR system.
  • New cylinder head with externally mounted injectors for easier servicing.
  • Redesigned intake manifold for better cylinder airflow.
  • Return to a grey cast iron block (no longer CGI).
  • New piston design with lower 16.0:1 compression.
  • ZF PowerLine 8-speed standard across all models.

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Cold weather impacts diesel engines more severely than gasoline engines, and this isn’t solely because of the engines themselves. By design, diesel engines are more difficult to turn over and start, and low temperatures make this challenge even greater. In fact, studies suggest that at zero degrees Fahrenheit, a diesel engine can be up to five times harder to start compared to at 80 degrees. Additionally, other conditions related to diesel fuel also come into play.

Startup Compression Temperatures

Diesel engines ignite fuel using hot air generated by compression rather than a spark, as in gasoline engines. Because air heats up when compressed, diesels rely on much higher compression ratios—often about double those of gas engines—to achieve ignition temperatures. This higher compression makes it more difficult for the starter motor to turn the engine, demanding greater electrical output from the battery. For this reason, many diesel-powered vehicles, especially larger pickup trucks, are equipped with two batteries.

Cold weather worsens the issue since batteries lose a significant amount of their capacity in low temperatures—estimates suggest as much as a 60% drop at zero degrees Fahrenheit compared to 80 degrees. While this power loss impacts both gas and diesel engines, the extra demands of a diesel put even more strain on the battery in cold conditions.

Because compression alone might not heat cold air sufficiently to ignite fuel, many diesels use glow plugs. These small electric heaters, located at the top of the cylinder, warm the chamber before startup. However, glow plugs also consume battery power, meaning the battery must deliver energy before the engine even begins cranking.

Additionally, low temperatures thicken engine oil, increasing friction between moving parts and making it harder to circulate—an issue that affects both diesel and gasoline engines.

Fuel

Both gasoline and diesel engines can be affected by water in the fuel. In cold weather, moisture can condense inside the fuel tank, forming droplets that may mix with the fuel and freeze in the lines, causing blockages. To reduce this risk, it helps to keep the tank at least half full or to use a fuel additive designed to prevent fuel line freezing.

Diesel engines, however, face an additional challenge that gasoline engines do not. Standard No. 2 diesel fuel contains paraffin wax to improve combustion efficiency. Unfortunately, low temperatures can cause this wax to solidify into a gel-like form, which may clog filters and fuel lines. To counteract this, many fuel stations switch to No. 1 diesel—or “winter diesel”—during colder months. This type of diesel is more refined, less prone to gelling, and typically more expensive. In some cases, stations may offer a blend of No. 1 and No. 2 diesel depending on the weather.

Drivers can also use anti-gel additives to reduce the risk of fuel gelling, but these must be added before filling the tank so they mix properly, and ideally before temperatures drop below freezing. Without this precaution, a tank of No. 2 diesel purchased in the fall could end up gelling in the middle of winter.

DEF

Beginning with many 2010 models, diesel vehicles are required to use diesel exhaust fluid (DEF) to comply with emissions standards. DEF is sprayed into the exhaust system, so it doesn’t influence how the engine starts or runs directly. The challenge, however, is that DEF is primarily water and can freeze at around 12°F. To make matters more restrictive, a diesel vehicle will not start if the DEF tank is empty.

Although DEF inside the vehicle’s tank is usually safe from freezing—often thanks to built-in heaters—the same cannot be said for DEF containers stored in a cold garage. If you let the DEF tank run low and then attempt to refill it with fluid that has frozen in storage, you’ll be stuck until it thaws.

Diesel engines, especially in cars and larger pickups, are admired for their fuel economy and towing capability, but these advantages come with added expenses and occasional challenges.

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