Silverado 2500 6.6L Gas V8 (L8T): Specs, MPG, and Towing
Silverado 2500 6.6L Gas V8 (L8T): Specs, MPG, and Towing
The Silverado 2500 6.6L gas V8, known internally by the engine code L8T, is the upgraded gas option on Chevrolet’s heavy-duty platform, sitting between the standard 6.0L V8 and the 6.6L Duramax diesel.
At McFarland Chevrolet in Maysville, KY, the L8T comes up regularly with buyers who want stronger gas performance and higher towing capacity than the base engine delivers, without the added cost and maintenance of the diesel. This page covers every confirmed spec on the L8T: horsepower, torque, towing capacity, fuel economy, oil requirements, and what owners actually report after putting real miles on it.
What Is the L8T Engine?
L8T is GM’s internal engine code for the 6.6L gas V8 used in the Silverado and Sierra 2500HD and 3500HD lineup. It is part of the same Gen V Small Block V8 family as the 5.3L and 6.2L engines used in the Silverado 1500, sharing core architecture while being built specifically for heavy-duty truck applications.
When the L8T was introduced
The L8T was introduced for the 2020 model year, replacing the previous-generation 6.0L Vortec as the upgraded gas engine option on the heavy-duty platform. It has been the standard 6.6L gas offering on the 2500HD and 3500HD continuously since then, including on the current 2026 lineup.
What is the L8T engine?
L8T is GM’s engine code for the 6.6L gas V8 used in the Silverado and Sierra 2500HD and 3500HD. It is part of the Gen V Small Block V8 family shared with the 5.3L and 6.2L engines in the Silverado 1500, built specifically for heavy-duty truck applications.
When did the Chevy 6.6L gas engine come out?
The L8T 6.6L gas V8 was introduced for the 2020 model year on the Silverado and Sierra 2500HD and 3500HD, replacing the previous 6.0L Vortec as the upgraded gas engine option on the heavy-duty platform.
2026 Silverado 2500 6.6L Gas V8 (L8T) Specs
Here are the core specifications for the L8T as equipped on the 2026 Silverado 2500HD.
Displacement: 6.6 liters, V8, naturally aspirated
Horsepower: 401 hp at 5,200 rpm
Torque: 464 lb-ft at 4,000 rpm
Transmission: 6-speed automatic. This is a key distinction from the Duramax diesel and the standard 6.0L, both of which use different transmission pairings on the platform; confirm the exact transmission for any specific build.
Max Towing: Up to approximately 17,530 lbs when properly equipped with the right axle ratio and towing package, the highest gas-engine towing figure on the platform.
Fuel requirement: Regular unleaded 87 octane. Premium is not required.
What is the horsepower and torque of the 6.6L V8 gas engine?
The L8T 6.6L gas V8 produces 401 horsepower at 5,200 rpm and 464 lb-ft of torque at 4,000 rpm on the current Silverado 2500HD lineup.
What is the towing capacity of the 6.6L gas V8?
The L8T 6.6L gas V8 can tow up to approximately 17,530 lbs when properly equipped with the right axle ratio and towing package, the highest towing figure of any gas engine on the Silverado 2500HD platform. Confirm the exact rating for a specific truck on the door jamb sticker, since configuration affects the final number.
Silverado 2500 6.6L Gas V8 Fuel Economy
Heavy-duty trucks are not required to display EPA fuel economy ratings the way half-ton trucks and passenger vehicles are, so GM does not publish an official combined MPG figure for the L8T the way it does for the Silverado 1500 engines. Real-world owner reports are the most reliable source for what to expect.
What owners actually report
Owner-reported fuel economy on the L8T generally falls in the 10 to 13 mpg range unloaded, with city driving and towing pulling that down further. This is consistent with what a naturally aspirated 6.6L V8 moving a heavy-duty truck chassis is expected to return. Buyers comparing the L8T against the Duramax diesel specifically for fuel economy should expect the diesel to outperform it meaningfully, particularly under sustained towing load.
What is the gas mileage on a Silverado 2500 6.6L V8?
GM does not publish an official EPA combined MPG figure for the L8T 6.6L gas V8, since heavy-duty trucks are not required to display fuel economy ratings. Owner-reported real-world fuel economy generally falls in the 10 to 13 mpg range unloaded, with towing reducing that further.
L8T Maintenance: Oil Type, Capacity, and Service Notes
The L8T is a naturally aspirated gas engine without the turbocharger or diesel-specific maintenance items the other 2500HD engines carry, which keeps its service requirements relatively straightforward.
Oil type and capacity
Full synthetic oil meeting Dexos 1 Gen 3 specification is required. Oil capacity on the L8T is approximately 8 quarts, slightly more than the 5.3L V8 in the 1500 lineup due to the larger displacement. Follow the oil life monitor for change intervals under normal driving rather than a fixed mileage.
Other routine service
Spark plugs follow the standard GM heavy-duty interval, typically reviewed around 100,000 miles. Air filter checks at each oil change. Because the L8T has no turbocharger, diesel exhaust fluid, or diesel fuel filter to manage, its maintenance schedule is the simplest of the three engines available on the 2500HD.
What oil does the Chevy 6.6L gas engine take?
The L8T 6.6L gas V8 requires full synthetic oil meeting Dexos 1 Gen 3 specification. Oil capacity is approximately 8 quarts. Follow the vehicle’s oil life monitor for change intervals under normal driving conditions.
L8T Reliability: What Owners Report
Buyers researching the L8T want an honest answer about reliability, and the honest answer is that this engine does not carry a widely documented problem pattern comparable to issues seen on other GM engines.
No widespread documented issue
Unlike the 5.3L and 6.2L EcoTec3 engines in the Silverado 1500, which have a documented AFM lifter concern on certain model years, the L8T does not use Active Fuel Management or Dynamic Fuel Management cylinder deactivation. That removes one of the most commonly reported failure points on GM’s other small block engines from the picture entirely. As of now, there is no widely reported, well-documented mechanical problem pattern specific to the L8T comparable to the AFM lifter issue.
What this means for buyers
A clean reliability record this early in an engine’s production life is a reasonable positive signal, but it is not the same as decades of accumulated high-mileage data the way the 5.3L V8 has. For used buyers, the standard inspection practices still apply: pull service records, check oil condition, and listen for unusual noise at operating temperature, the same as on any used engine regardless of its documented history.
Are there any known issues with the GM 6.6L gas engine?
There is no widely documented, well-established mechanical problem pattern specific to the L8T 6.6L gas V8 at this time. It does not use Active Fuel Management or Dynamic Fuel Management cylinder deactivation, which removes one of the more commonly reported concerns seen on other GM small block engines. Standard maintenance and the usual used-vehicle inspection practices still apply.
L8T vs the Standard 6.0L and the Duramax Diesel
The L8T sits in the middle of the 2500HD’s three-engine lineup, and understanding where it fits helps clarify whether it is the right choice for your truck. The standard 6.0L V8 produces 360 hp and 380 lb-ft of torque with towing up to approximately 14,500 lbs, making the L8T a meaningful step up in both power and capability for buyers who want more from a gas engine without going to diesel. The 6.6L Duramax diesel produces 470 hp and 975 lb-ft of torque with towing up to 18,500 lbs on a properly configured gooseneck setup, exceeding the L8T’s capability but at a higher purchase cost and with diesel-specific maintenance requirements. The full comparison across all three engines, including hitch-type towing breakdowns, is on our 2500 towing capacity by engine guide.
Should I get the 6.6L gas or the Duramax diesel?
If your towing stays under approximately 17,000 lbs and you want lower purchase cost and simpler maintenance, the L8T 6.6L gas V8 is a strong choice. If you regularly tow at the upper end of the platform’s capability or drive significant highway miles where diesel fuel economy pays off over time, the Duramax is the better long-term choice. Our diesel vs gas comparison covers the full decision in detail.
Which Silverado 2500HD Trims Offer the L8T?
The L8T is available as an engine upgrade across the 2500HD trim lineup, including the Work Truck. Choosing a lower trim like the Work Truck or Custom does not limit access to the L8T; the full engine lineup carries across every trim level on the platform.
Can you get the 6.6L gas engine on a Work Truck trim Silverado 2500?
Yes. The L8T 6.6L gas V8 is available as an engine upgrade on every Silverado 2500HD trim, including the base Work Truck. Choosing a lower trim does not limit engine availability on the platform.
The L8T at McFarland Chevrolet
McFarland Chevrolet has been family-owned in Maysville, KY since 1983. The L8T is a regular recommendation for buyers across Mason County who want more capability than the standard 6.0L without the diesel’s added cost. Caleb McFarland has driven a 2006 Silverado 2500 Duramax since he was a teenager, so when buyers ask us to walk through gas versus diesel on the 2500HD, the answer comes from someone who knows both sides of that decision firsthand.
Ready for Your Next Step?
Tell us what you tow and how often, and we will tell you straight whether the L8T or the Duramax is the right call for your situation. Call us at (606) 564-6181.