The GMC Sierra 3500HD IV (GMTK2XX) Double Cab Long Box, specifically equipped with the 6.0-liter V8 engine producing 301 horsepower and paired with a 4WD automatic transmission, and capable of running on Compressed Natural Gas (CNG), was produced for the 2015 and 2016 model years. This variant occupied a significant position within the fourth generation of the Sierra 3500HD lineup, catering to buyers needing substantial towing and hauling capacity with an alternative fuel option. It represented a blend of traditional heavy-duty truck capability and a step towards more environmentally conscious operation, albeit limited by the infrastructure for CNG refueling.
Technical Specifications
| Brand | GMC |
| Model | Sierra 3500HD |
| Generation | Sierra 3500HD IV (GMTK2XX) Double Cab Long Box |
| Type (Engine) | 6.0 V8 (301 Hp) 4WD 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%) | 3992 kg / 8800.85 lbs. |
| Length | 6321 mm / 248.86 in. |
| Width including mirrors | 2045 mm / 80.51 in. |
| Height | 1980 mm / 77.95 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) | 223 mm / 8.78 in. |
| Minimum turning circle (turning diameter) | 16.2 m / 53.15 ft. |
| Drivetrain Architecture | The Internal combustion engine (ICE) drives the rear wheels permanently, and the front wheels are driven through an electrically or mechanically operated clutch if necessary. |
| Drive wheel | All wheel drive (4×4) |
| 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 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 multi-port fuel injection system. The overhead valve (OHV) valvetrain, while not as sophisticated as overhead cam designs, contributes to the engine’s durability and ease of maintenance. Variable Valve Timing (VVT) was incorporated to improve efficiency and low-end torque. The engine’s ability to run on CNG is achieved through a dedicated fuel system that supplements or replaces gasoline operation. The Hydra-Matic 6L90 six-speed automatic transmission was the standard pairing, chosen for its ability to handle the engine’s torque output and provide smooth shifting. This transmission features electronically controlled shifting and overdrive for improved fuel economy at highway speeds.
Driving Characteristics
The 301 horsepower and 333 lb-ft of torque delivered by the 6.0L V8, while substantial, positioned this Sierra 3500HD as a mid-range offering within the lineup. Compared to the available Duramax diesel engines, it offered less low-end grunt for heavy towing, but a more familiar and generally less expensive ownership experience. The automatic transmission, while smooth, wasn’t as responsive as the available manual transmission. Gear ratios were optimized for towing and hauling, resulting in a slightly lower final drive ratio compared to trims focused solely on on-road performance. In real-world conditions, this meant confident acceleration when unladen, but a noticeable reduction in responsiveness when heavily loaded. The CNG capability offered a potential cost savings on fuel, but was limited by the availability of CNG refueling stations.
Equipment & Trim Levels
The Double Cab Long Box configuration provided ample passenger space and a generous cargo bed. Standard equipment 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 badging and instrumentation to indicate their alternative fuel capability. Optional extras included a trailer brake controller, upgraded suspension packages, and various appearance enhancements.
Chassis & Braking
The Sierra 3500HD’s chassis was built for heavy-duty use. It featured a fully boxed frame and a robust suspension system designed to handle significant payloads and towing loads. The front suspension utilized coil springs and a double wishbone design, while the rear suspension employed leaf springs. This configuration prioritized load-carrying capacity over ride comfort. Brakes consisted of ventilated discs at all four corners, providing adequate stopping power for the truck’s weight. An Anti-lock Braking System (ABS) was standard. The rear axle ratios varied depending on the specific configuration, with lower ratios favored for towing and higher ratios for improved fuel economy.
Market Reception & Comparison
The 6.0L V8/automatic combination in the Sierra 3500HD was generally well-received as a capable and affordable option for buyers who didn’t require the ultimate towing capacity of the diesel models. Critics praised the engine’s reliability and relatively low maintenance costs. However, fuel economy was a concern, particularly when compared to the diesel alternatives. The CNG option was seen as a positive step towards reducing emissions, but its practicality was limited by the lack of widespread CNG infrastructure. Compared to the diesel trims, this variant offered a lower initial purchase price but higher long-term fuel costs, making it a more attractive option for buyers who primarily used the truck for lighter-duty tasks.
Legacy
The Vortec LC8 engine, in general, has proven to be a durable and reliable powerplant. While not without its potential issues (such as oil consumption in some cases), it is generally considered a relatively trouble-free engine when properly maintained. The 6L90 transmission is also known for its robustness. In the used car market, the 2015-2016 Sierra 3500HD with the 6.0L V8 and CNG capability represents a unique offering. Its value is influenced by mileage, condition, and the availability of CNG refueling stations in the buyer’s area. These trucks continue to be sought after by buyers who need a heavy-duty truck with a gasoline engine and appreciate the potential cost savings of CNG.
