The GMC Sierra 3500HD IV (GMTK2XX) Double Cab Long Box with the 6.0-liter V8 engine and automatic transmission, offered with a Compressed Natural Gas (CNG) conversion, was a heavy-duty pickup truck produced for the 2015 and 2016 model years. This variant occupied a middle ground within the Sierra 3500HD lineup, offering a balance between capability, comfort, and alternative fuel operation. It was part of the fourth generation of the Sierra/Silverado HD series, known as the GMTK2XX platform, which represented a significant redesign focused on increased strength, refinement, and technology.
Technical Specifications
| Brand | GMC |
| Model | Sierra 3500HD |
| Generation | Sierra 3500HD IV (GMTK2XX) Double Cab Long Box |
| Type (Engine) | 6.0 V8 (301 Hp) Automatic CNG |
| Start of production | 2015 |
| End of production | 2016 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Pick-up |
| Seats | 5 |
| Doors | 4 |
| 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 |
| Permitted trailer load with brakes (12%) | 4128 kg / 9100.68 lbs. |
| Length | 6321 mm / 248.86 in. |
| Width including mirrors | 2045 mm / 80.51 in. |
| Height | 1981 mm / 77.99 in. |
| Wheelbase | 4017 mm / 158.15 in. |
| Front track | 1748 mm / 68.82 in. |
| Rear (Back) track | 1709 mm / 67.28 in. |
| Ride height (ground clearance) | 221 mm / 8.7 in. |
| Minimum turning circle (turning diameter) | 16.2 m / 53.15 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, 373×34 mm |
| Assisting systems | ABS (Anti-lock braking system) |
| Steering type | Cone worm with recirculation balls |
| Tires size | 235/80 R17; 265/70 R18 |
| Wheel rims size | 7.5J x 17; 8J x 18 |
Powertrain & Engine Architecture
At the heart of this Sierra 3500HD was the Vortec LC8 6.0-liter V8 engine. This engine, a staple of GM’s heavy-duty truck lineup for many years, is a cast-iron block, aluminum-head design. It featured a 9.6:1 compression ratio and utilized multi-port fuel injection. The overhead valve (OHV) valvetrain, while traditional, was paired with variable valve timing (VVT) to improve efficiency and low-end torque. The engine produced 301 horsepower at 5000 rpm and 452 Nm (333.38 lb-ft) of torque at 4200 rpm. The addition of a CNG conversion allowed the truck to operate on either gasoline or compressed natural gas, offering potential cost savings and reduced emissions, though with a decrease in overall power output when running solely on CNG.
The engine was mated to a six-speed Hydra-Matic automatic transmission. This transmission was known for its durability and smooth shifting characteristics, well-suited for the demands of heavy towing and hauling. The automatic transmission provided a convenient driving experience, particularly in urban environments, and was a popular choice for buyers who didn’t prefer a manual transmission.
Driving Characteristics
The 6.0-liter V8 with the automatic transmission delivered a capable, if not particularly sporty, driving experience. While the engine provided ample torque for towing and hauling, the automatic transmission’s programming prioritized smooth operation over aggressive shifting. Compared to the available 6.6-liter Duramax diesel engine, the 6.0-liter gasoline V8 offered less low-end torque and lower fuel economy, but it was significantly less expensive to purchase and maintain. The CNG conversion further impacted performance, reducing horsepower and torque when operating on natural gas. However, the CNG system provided a quieter engine operation and reduced emissions.
Equipment & Trim Levels
The Double Cab Long Box configuration offered a spacious interior with seating for five passengers. Standard features typically included air conditioning, power windows and locks, a basic audio system, and vinyl upholstery. Higher trim levels, such as the SLT and Denali, added features like leather upholstery, heated seats, a premium audio system, navigation, and advanced safety technologies. The CNG-equipped models often included specific gauges and controls related to the alternative fuel system. Options such as a sunroof, upgraded wheels, and various towing packages were also available.
Chassis & Braking
The Sierra 3500HD featured a robust chassis designed for heavy-duty use. The front suspension utilized coil springs and a double wishbone design, while the rear suspension employed a traditional leaf spring setup. This configuration provided a comfortable ride while maintaining excellent load-carrying capacity. Brakes consisted of ventilated discs at all four wheels, providing ample stopping power. An Anti-lock Braking System (ABS) was standard equipment. The rear axle ratios were selected to optimize towing performance and fuel economy, depending on the specific configuration.
Market Reception & Comparison
The GMC Sierra 3500HD with the 6.0-liter V8 and automatic transmission was generally well-received by critics and consumers. It was praised for its comfortable ride, spacious interior, and strong towing capabilities. However, the gasoline engine’s fuel economy was a common criticism, especially compared to the diesel option. The CNG conversion was seen as a niche offering, appealing to fleet operators and environmentally conscious buyers. Compared to the diesel-powered Sierra 3500HD, the gasoline version was more affordable to purchase but had higher operating costs due to fuel consumption and maintenance.
Legacy
The GMTK2XX generation Sierra 3500HD, including the 6.0-liter V8/automatic CNG variant, has proven to be a durable and reliable truck. The Vortec LC8 engine, while not as fuel-efficient as modern engines, is known for its longevity and relatively simple maintenance requirements. The Hydra-Matic transmission is also considered a robust unit. Today, these trucks are commonly found in the used car market, often with high mileage but still capable of performing demanding tasks. The CNG conversions, while requiring specialized maintenance, can offer long-term cost savings for owners who have access to affordable natural gas. The Sierra 3500HD remains a popular choice for those seeking a capable and dependable heavy-duty pickup truck.
