The GMC Sierra 2500HD III, specifically the Regular Cab Long Box configuration with the 6.0L V8 engine paired to an automatic transmission and capable of running on Compressed Natural Gas (CNG), was produced for a limited run between 2013 and 2014. This variant represented a niche offering within the GMT900 platform – a facelift of the third-generation Sierra HD series – aimed at customers requiring heavy-duty capability with an alternative fuel option. It occupied a middle ground in the 2500HD lineup, offering a balance between power, towing capacity, and the potential cost savings associated with CNG fuel.
Technical Specifications
| Brand | GMC |
| Model | Sierra 2500HD |
| Generation | Sierra 2500HD III (GMT900, facelift 2011) Regular Cab Long Box |
| Type (Engine) | 6.0 V8 (301 Hp) Automatic CNG |
| Start of production | 2013 |
| End of production | 2014 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Pick-up |
| Seats | 2 |
| Doors | 2 |
| Fuel Type | Petrol / CNG |
| Power | 301 Hp @ 5000 rpm |
| Power per litre | 50.4 Hp/l |
| Torque | 452 Nm @ 4200 rpm / 333.38 lb.-ft. @ 4200 rpm |
| Maximum engine speed | 6000 rpm |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | Vortec LC8 |
| Engine displacement | 5967 cm3 / 364.13 cu. in. |
| Number of cylinders | 8 |
| Engine configuration | V-engine |
| Cylinder Bore | 101.6 mm / 4 in. |
| Piston Stroke | 92 mm / 3.62 in. |
| Compression ratio | 9.6:1 |
| Number of valves per cylinder | 2 |
| Fuel injection system | Multi-port manifold injection |
| Engine aspiration | Naturally aspirated engine |
| Valvetrain | OHV, VVT |
| Engine oil capacity | 5.7 l / 6.02 US qt | 5.02 UK qt |
| Coolant | 15.5 l / 16.38 US qt | 13.64 UK qt |
| Fuel tank capacity | 136 l / 35.93 US gal | 29.92 UK gal |
| CNG cylinder capacity | 67 kg |
| Length | 5715 mm / 225 in. |
| Width including mirrors | 2032 mm / 80 in. |
| Height | 1971 mm / 77.6 in. |
| Wheelbase | 3369 mm / 132.64 in. |
| Front track | 1748 mm / 68.82 in. |
| Rear (Back) track | 1709 mm / 67.28 in. |
| Ride height (ground clearance) | 231 mm / 9.09 in. |
| Minimum turning circle (turning diameter) | 13.7 m / 44.95 ft. |
| Drivetrain Architecture | The Internal combustion engine (ICE) drives the rear wheels of the vehicle. |
| Drive wheel | Rear wheel drive |
| Number of gears and type of gearbox | 6 gears, automatic transmission Hydra-Matic |
| Front suspension | Coil spring, Double wishbone, Transverse stabilizer |
| Rear suspension | Rigid axle suspension, Leaf spring |
| Front brakes | Ventilated discs, 350×40 mm |
| Rear brakes | Ventilated discs, 360×34 mm |
| Assisting systems | ABS (Anti-lock braking system) |
| Steering type | Cone worm with recirculation balls |
| Tires size | 245/75 R17; 265/70 R17; 265/70 R18; 265/60 R20 |
| Wheel rims size | 7.5J x 17; 8J x 18; 8.5J x 20 |
Powertrain & Engine Architecture
At the heart of this Sierra 2500HD variant lies the Vortec LC8 engine, a 6.0-liter (364 cubic inch) V8. This engine is a member of the Vortec family, known for its robust construction and relatively simple design. It features a cast iron block and aluminum cylinder heads, utilizing a 9.6:1 compression ratio and a two-valve-per-cylinder OHV (Overhead Valve) configuration with Variable Valve Timing (VVT). Fuel delivery is managed by a multi-port fuel injection system. The LC8 produces 301 horsepower at 5000 rpm and 452 Nm (333.38 lb-ft) of torque at 4200 rpm. The engine was designed to provide ample low-end torque, crucial for heavy-duty tasks like towing and hauling. The automatic transmission used is a 6-speed Hydra-Matic, chosen for its durability and ability to handle the engine’s output. The addition of CNG capability required a dedicated fuel system alongside the gasoline system, including a CNG tank (67 kg capacity) and associated regulators and injectors.
Driving Characteristics
The 6.0L V8 with the 6-speed automatic transmission delivers a noticeable balance between power and usability. While not as quick as some of the diesel-powered 2500HD models, it provides sufficient power for most tasks. The automatic transmission is tuned for smooth shifts and emphasizes torque delivery over outright acceleration. The gear ratios are optimized for towing and hauling, meaning the engine operates efficiently within its powerband when under load. Compared to the manual transmission options, the automatic offers greater convenience, especially in stop-and-go traffic. The CNG system, when utilized, can slightly reduce overall power output compared to running solely on gasoline, but it also offers potential fuel cost savings. The ride quality, typical of a heavy-duty truck, is firm but generally comfortable for a work-oriented vehicle.
Equipment & Trim Levels
The 2500HD Regular Cab Long Box with the 6.0L CNG engine was typically offered with a base level of equipment, focusing on functionality rather than luxury. Standard features included air conditioning, a basic audio system, vinyl upholstery, and manually adjustable windows and locks. Optional extras could include power windows and locks, upgraded audio systems, and various towing packages. The interior was designed with durability in mind, featuring hard-wearing materials and a straightforward layout. The Regular Cab configuration meant limited passenger space, making it best suited for work-focused applications.
Chassis & Braking
The Sierra 2500HD utilizes a body-on-frame construction, providing a robust platform for heavy-duty applications. The front suspension consists of coil springs and a double wishbone setup with a transverse stabilizer bar. The rear suspension employs a traditional leaf spring design, known for its load-carrying capacity. Braking duties are handled by ventilated discs on all four wheels, with ABS (Anti-lock Braking System) as standard. The rear brakes are slightly smaller in diameter (360×34 mm) compared to the front (350×40 mm). The steering system is a cone worm with recirculation balls, providing a direct but somewhat heavy steering feel.
Market Reception & Comparison
The 2500HD with the 6.0L CNG engine received mixed reviews. Critics acknowledged the potential cost savings offered by CNG, but also noted the limited availability of CNG refueling stations. Compared to the diesel-powered 2500HD models (particularly those with the Duramax engine), the 6.0L gasoline engine offered less torque and lower fuel economy when running on gasoline. However, it was generally more affordable to purchase initially. Compared to the smaller 5.3L V8 option, the 6.0L provided a significant power upgrade, making it a more suitable choice for demanding tasks. The CNG variant appealed to fleet operators and individuals seeking to reduce their carbon footprint and potentially lower fuel costs.
Legacy
The 6.0L Vortec LC8 engine, in general, has a reputation for being a reliable and durable powerplant, although it is known to be susceptible to oil consumption issues as it ages. The automatic transmission is also generally considered robust. The CNG conversion adds complexity to the fuel system, potentially increasing maintenance requirements. Today, these trucks are found primarily in the used market, often with significant mileage. The CNG system may require periodic inspection and maintenance to ensure safe and reliable operation. While not as sought-after as the diesel variants, the 6.0L CNG Sierra 2500HD represents a unique and interesting option for those seeking a heavy-duty truck with an alternative fuel capability.
