We’ve made plenty of articles that talk about the specifications of various pickup trucks, such as the GMC Sierra.
But for this article, we’re going to specifically dive into the types of gas that different GMC Sierra models can and cannot take, which will come in handy to avoid damaging their engines.
Much like its nearly identical counterpart, the Chevy Silverado, the GMC Sierra will have its own set of fuel requirements that’s worth taking note of when you’re in the market for one.
What kind of gas does a GMC Sierra take?
Gasoline-powered GMC Sierra models from 1988 to 2006 can take regular 87-octane gas, while some 2007 to 2019 models with 5.3, 6.0, and 6.2-liter engines require 91-octane.
2014 to 2019 6.0-liter models and 2020 to present 6.2-liter models need 93-octane gas, while all diesel models only use diesel.
Even with the short summary of fuel requirements for the GMC Sierra above, it can still be a bit confusing to keep track of each engine’s needs.
This is why we’ve listed all of the GMC Sierra’s fuel requirements according to the specific generation and engine option in the next part.
The lists also include all of the GMC Sierra “Flex-Fuel” models that are capable of using gasoline blended with up to 85% ethanol (E-85).
GMC Sierra Fuel Requirements Based On Generation and Engine Option
1st and 2nd-generation GMC Sierra models with gasoline engines require 87-octane fuel, while some 3rd to 5th-generation models require either premium 91 or 93-octane fuel.
Some 3rd to 5th-generation GMC Sierra models are also flex-fuel capable, while all diesel options should only use diesel fuel.
1st-Generation GMC Sierra (GMT400) (1988 to 1998)
| Engine Option | Minimum Fuel Requirement |
| 4.3L Vortec 4300 V6 | 87-Octane Gasoline (Regular) |
| 5.0L Vortec 5000 V8 | 87-Octane Gasoline (Regular) |
| 5.7L Vortec 5700 V8 | 87-Octane Gasoline (Regular) |
| 7.4L Vortec 7400 V8 | 87-Octane Gasoline (Regular) |
| 6.2L Detroit Diesel V8 | Diesel Fuel |
| 6.5L Detroit Diesel V8 | Diesel Fuel |
The 1st-generation GMC Sierra was built on the “GMT400” platform for the 1988 to 1998 model years.
The GMT400 GMC Sierra was offered with 4 different gasoline engines that can take regular 87-octane gasoline. Three of those engines are Vortec V8s, while the remaining is the sole Vortec V6 option.
As for the diesel models, you have choices of either a 6.2-liter or a 6.5-liter Detroit Diesel V8 that, of course, only takes diesel fuel.
2nd-Generation GMC Sierra (GMT800) (1999 to 2006)
| Engine Option | Minimum Fuel Requirement |
| 4.3L Vortec 4300 V6 | 87-Octane Gasoline (Regular) |
| 4.8L Vortec 4800 V8 | 87-Octane Gasoline (Regular) |
5.3L Vortec 5300 V8 | 87-Octane Gasoline (Regular)(E-85/Flex-Fuel Option Available in Non-California Emissions States) |
| 6.0L Vortec 6000 V8 (HD Models) | 87-Octane Gasoline (Regular) |
| 8.1L Vortec 8100 V8 (HD Models) | 87-Octane Gasoline (Regular) |
| 6.6L Duramax V8 Turbo Diesel (HD Models) | Diesel Fuel |
The 2nd-generation GMC Sierra was first introduced in 1998 for the 1999 model year under the “GMT800” platform.
It was with this that the GMC Sierra shared the same platform with the 1st-generation Chevy Silverado for the first time.
Almost all of the engines from the previous generation have not been carried over to the 2nd-generation GMC Sierra, with the only exception being the smallest 4.3-liter Vortec V6 option.
The other Vortec engines that were new for this generation model were the 4.8-liter, 5.3-liter, 6-liter, and 8.1-liter V8s, though the latter two can only be found in the HD (Heavy-Duty) models.
All of the above-mentioned engines are gasoline engines that can take regular 87-octane gasoline.
Though for the 2003 model year facelift, a GMC flex-fuel option was specifically offered for the 5.3-liter V8 model.
However, this GMC Sierra flex-fuel model was only available in states that did not follow California emissions standards.
The only engine option of the GMT800 generation that doesn’t take gasoline would be the turbocharged 6.6-liter Duramax V8 diesel, which replaced the previous two Detroit Diesel engines.
3rd-Generation GMC Sierra (GMT900) (2007 to 2013)
| Engine Option | Minimum Fuel Requirement |
| 4.3L Vortec 4300 V6 | 87-Octane Gasoline (Regular) or Higher |
| 4.8L Vortec 4800 V8 | 87-Octane Gasoline (Regular) or Higher(E-85/Flex-Fuel Capable) |
| 5.3L Vortec 5300 V8 | 91-Octane Gasoline (Premium) or Higher(E-85/Flex-Fuel Capable) |
| 6.0L Vortec 6000 V8 (HD Models) | 91-Octane Gasoline (Premium) or Higher(E-85/Flex-Fuel Capable) |
| 6.2L Vortec 6200 V8 | 91-Octane Gasoline (Premium) or Higher(E-85/Flex-Fuel Capable) |
| 6.6L Duramax V8 Turbo Diesel (HD Models) | Diesel Fuel |
The 3rd-generation GMC Sierra, under the “GMT900” platform, was made for the 2007 to 2013 model years of the pickup truck, and most of the engines from the previous generation were carried over to it.
However, the 8.1-liter Vortec V8 was no longer offered, as the newer 6.2-liter Vortec V8 took its place as the gasoline engine with the largest displacement in the lineup.
Also, the 5.3-liter, 6-liter, and 6.2-liter V8s of this generation now require premium 91-octane gasoline instead of just regular 87-octane.
Another big change to the 3rd-generation GMC Sierra’s lineup of gasoline engines is that most of them are now capable of taking E-85 or Flex-Fuel.
Though to be sure that a 3rd-generation GMC Sierra is actually flex-fuel capable, we recommend following the short guide below.
3rd-Generation GMC Sierra models with Flex-Fuel capability will have the following numbers or letters on the 8th digit of their VIN:
5.3L Vortec V8 – 0 or 3
6.0L Vortec V8 – J
6.2L Vortec V8 – 2
Also, you can check the color of the gas cap, as Flex-Fuel vehicles (FFVs) will have a yellow fuel cap with “E-85” printed on it.
4th-Generation GMC Sierra (GMT K2XX) (2014 to 2019)
| Engine Option | Minimum Fuel Requirement |
| 4.3L Ecotec3 V6 | 87-Octane Gasoline (Regular) or Higher(E-85/Flex-Fuel Capable) |
| 5.3L Ecotec3 V8 | 87-Octane Gasoline (Regular) or Higher(E-85/Flex-Fuel Capable) |
| 6.2L Ecotec3 V8 | 91-Octane Gasoline (Premium) or Higher(E-85/Flex-Fuel Capable) |
| 6.0L Vortec 6000 V8 (HD Models) | 93-Octane Gasoline (Premium)(E-85/Flex-Fuel Capable) |
| 6.6L Duramax V8 Turbo Diesel (HD Models) | Diesel Fuel |
2014 to 2019 GMC Sierra model years are all part of the GMT K2XX platform, making them the 4th iteration of GMC’s popular pickup truck.
4th-generation GMC Sierra models have replaced the “Vortec” name in most of their engines in favor of newer EcoTec3 counterparts, with the only remaining Vortec engine being the 6-liter V8 option.
The new 4.3-liter Ecotec3 V6 and 5.3-liter Ecotec3 V8 options can both run on regular 87-octane fuel, while the 6.2-liter Ecotec3 V8 requires 91-octane fuel instead.
The 6-liter Vortec V8 that was carried over from the 3rd-generation model still requires premium 93-octane fuel in order to run properly and avoid engine knock.
Likewise, the 6.6-liter Duramax turbodiesel V8 engine used ever since the 2nd generation still finds its home in the 4th-generation “HD/Heavy-Duty” models, though more updated versions of it (LML/L5P).
It’s also important to mention that all of the gasoline engines for the 4th-generation GMC Sierra are flex-fuel capable, so you won’t have trouble using gasoline with up to an 85% ethanol blend E-85).
5th-Generation GMC Sierra (GMT T1XX) (2019 to 2023/Present)
| Engine Option | Minimum Fuel Requirement |
| 2.7L Inline-4 (I4) Turbo | 87-Octane Gasoline (Regular) or Higher |
| 4.3L Ecotec3 V6 | 87-Octane Gasoline (Regular) or Higher(E-85/Flex-Fuel Capable) |
| 5.3L Ecotec3 V8 | 87-Octane Gasoline (Regular) or Higher(E-85/Flex-Fuel Capable) |
| 6.2L Ecotec3 V8 | 93-Octane Gasoline (Premium) |
| 3.0L Duramax Inline-6 (I6) Turbo Diesel | Diesel Fuel |
| 6.6L Duramax V8 Turbo Diesel | Diesel Fuel |
5th-generation GMC Sierra models are part of the GMT T1XX platform and are one of the newest pickup trucks offered by General Motors alongside the 6th-generation Chevy Silverado.
While the previous 4.3-liter, 5.3-liter, and 6.2-liter Ecotec3 engines were carried over, the 5th-generation model also offers a smaller turbocharged 2.7-liter Inline-4 (I4) engine for the first time.
Together with the 4.3-liter and 5.3-liter Ecotec3 engines, the new 2.7-liter I4 engine can take regular 87-octane gasoline.
On the other hand, the newest version of the 6.2-liter Ecotec3 V8 now requires premium 93-octane gasoline, a contrast to its older counterparts which only required 91-octane gasoline.
Types of Gasoline/Fuel That Can Be Used in a GMC Sierra
The GMC Sierra can use Top Tier detergent gasoline, reformulated gasoline, E-10 or E-15 blends (non-flex-fuel models), E-85 (flex-fuel models), and up to 20% biodiesel (Duramax diesel models).
Top Tier Detergent Gasoline (GMC’s Recommendation)
TOP TIER gasoline is one of the best fuels out there when it comes to engine cleaning, and this is thanks to its mixture of high-quality detergent additives.
Such detergent additives are able to provide your engine with better protection against the accumulation of any kind of deposits, debris, or gunk.
In turn, this enables the engine to operate smoother and maintain its performance throughout any sort of task.
This is quite useful for a vehicle like the GMC Sierra, as heavy tasks such as towing or carrying heavy loads on its truck bed demand more effort from the engine.
Not only is the TOP TIER formulation adopted by over 60 fuel brands across North America, but it’s also recommended by GMC and many other popular automakers for their vehicles.
Also, if you own or plan on buying a diesel variant of the GMC Sierra, then TOP TIER diesel fuel also exists for diesel applications.
However, TOP TIER diesel is a little bit trickier to find compared to TOP TIER gasoline, as only a few licensed retail brands in North America actually sell it.
You can spot any of the two types of TOP TIER fuel by looking for their respective labels on gas pumps, as shown below.
Reformulated Gasoline (RFG)
Reformulated gasoline is a more modern type of fuel that’s specifically formulated to burn more cleanly compared to the conventional gasoline sold in gas stations.
Reformulated gasoline’s cleaner emissions are a result of it containing less toxic ingredients that are known to contribute to the formation of ozone and other air toxins.
This makes it the go-to gasoline in areas that have higher concentrations of air pollution and smog.
About 25% of all gasoline sold in the US is reformulated gasoline, so it’s already quite a popular choice of fuel and is safe for use in many types of vehicles on the road, including the GMC Sierra.
Up to 10 or 15% Ethanol Blends (E-10/E-15) (Non-Flex-Fuel Models)
Gasoline-powered GMC Sierra models can actually take some amount of ethanol blended with the usual gasoline that they take.
However, it’s important to take note of the specific ethanol percentages that certain vehicle models can take safely.
According to the EPA, vehicle models manufactured before 2011 are capable of taking gasoline blended with up to 10% ethanol, otherwise known as “E-10”.
Vehicle models produced after 2011 have been allowed to run on as much as 15% ethanol mixed in gasoline, or “E-15”.
With that said, you should not use any sort of ethanol blend higher than E-10 or E-15 for non-flex-fuel GMC Sierra models.
You can confirm if a certain GMC Sierra model can only take up to E-10 or E-15 if it has a black fuel cap with the compatible fuel type printed on it.
E-85/Flex-Fuel (GMC Flex-Fuel Models)
There are several different GMC Sierra models that are “flex-fuel capable”, meaning that they are capable of taking gasoline that’s blended with up to 85% ethanol, or E-85.
| GMC Sierra Generation (E-85/Flex-Fuel) | Engine Option |
| 2nd Generation (2003 Facelift) | 5.3L Vortec 5300 V8 Flex-Fuel (Only Offered in Non-California Emissions States) |
| 3rd Generation (2007 to 2013) | 4.8L Vortec 4800 V8 |
| 5.3L Vortec 5300 V8 | |
| 6.0L Vortec 6000 V8 | |
| 6.2L Vortec 6200 V8 | |
| 4th Generation (2014 to 2019) | 4.3L Ecotec3 V6 |
| 5.3L Ecotec3 V8 | |
| 6.2L Ecotec3 V8 | |
| 6.0L Vortec 6000 V8 | |
| 5th Generation (2019 to 2023/Present) | 4.3L Ecotec3 V6 |
| 5.3L Ecotec3 V8 |
Since the listed engines are equipped in GMC flex-fuel vehicles, they will likely have a yellow fuel cap that indicates their capability of using flex-fuel or E-85.
Up to 20% Biodiesel Blends (B20) (Duramax Diesel Models)
Aside from using regular diesel, diesel-powered GMC Sierra models have also been designed to take biodiesel, though the percentage is limited to just 20%.
20% biodiesel blends, also known as B20, are known to reduce the emission of carbon dioxide, as they’re formulated to burn cleaner and be more renewable compared to conventional diesel.
Though it’s also important to mention that not every GMC Sierra diesel engine can take as much as 20% biodiesel.
According to a news article back in 2010, an announcement made by General Motors states that B20 biofuel capability is specifically being adapted for the 6.6-liter Duramax diesel engine.
The newer 3-liter Duramax diesel engine is also capable of taking B20 biodiesel, which leaves one other diesel engine left.
Upon further research, the older Detroit Diesel engines used in the 1st-generation GMC Sierra are not factory certified to run on biodiesel.
Thus, the safe use of B20 biodiesel is only limited to GMC Sierra models equipped with Duramax diesel engines.
Types of Gasoline/Fuel to Avoid for the GMC Sierra
Avoid filling up the GMC Sierra with gasoline containing MMT, gasoline with added materials like methanol, and gasoline with a lower octane rating than what’s recommended for that specific GMC engine.
Gasoline Containing MMT (Methylcyclopentadienyl Manganese Tricarbonyl)
There are countless fuel additives out there that are advertised to give some sort of benefit to your vehicle’s engine, whether it be to boost the octane rating or clean the internals.
However, some of them have been found to do more harm than good for both your engine and the environment, such as MMT.
MMT is a metallic-based additive that has been primarily used to boost the octane rating of both leaded and unleaded gasoline, thereby reducing the chance of engine knock as well.
Though the two main drawbacks of MMT are that it makes your vehicle’s emissions more toxic to the environment, and it can also cause damage to the spark plugs and other components of the emission system.
As a result of such downsides, many gasoline brands have chosen to be completely MMT-free. This is already a clear sign to stay away from using MMT on the GMC Sierra and many other vehicles.
Gasoline with Added Materials (Methanol, Methylal, Ferrocene, Aniline)
There are certain types of added materials, or “additives”, that should not be put in gasoline for the GMC Sierra, as its lineup of engines are not designed to take such additives without corroding the internals.
Since the GMC Sierra shares the same set of engines as the Chevy Silverado, prohibited additives like methanol, methylal, ferrocene, and aniline should also not be used for the former.
Instead, the best additive that you can put in the GMC Sierra would be the detergent additives that are already included in TOP TIER fuel, as we’ve discussed in the last section.
What will happen if I use the wrong gas type?
Using the wrong gas type can decrease the performance of your engine, cause engine knock, and potentially damage the internals.
For instance, such issues can happen when you put gasoline that has too low of an octane rating than what your vehicle requires.
Does the GMC Sierra get good gas mileage?
Most GMC Sierra models get low gas mileage (15/20 mpg city/hwy) compared to similar trucks from other brands.
GMC Sierra models that get the best mileage are the ones equipped with the 3-liter Duramax diesel engine.
GMC Sierra Gas Mileage Per Generation
Gasoline-powered GMC Sierra models have a combined gas mileage of 6 to 23 mpg depending on the generation.
Diesel-powered GMC Sierra models have a combined gas mileage of 8 to 26 mpg depending on the generation.
1st-Generation GMC Sierra Gas Mileage (GMT400) (1988 to 1998)
| Engine Option | Lowest Combined MPG | Highest Combined MPG |
| 4.3L Vortec 4300 V6 | 14 | 18 |
| 5.0L Vortec 5000 V8 | 12 | 16 |
| 5.7L Vortec 5700 V8 | 12 | 15 |
| 6.2L Detroit Diesel V8 | 16 | 20 |
| 6.5L Detroit Diesel V8 | 14 | 19 |
2nd-Generation GMC Sierra Gas Mileage (GMT800) (1999 to 2006)
| Engine Option | Lowest Combined MPG | Highest Combined MPG |
| 4.3L Vortec 4300 V6 | 15 | 20 |
| 4.8L Vortec 4800 V8 | 13 | 16 |
| 5.3L Vortec 5300 V8 | 14 | 18 |
| 6.0L Vortec 6000 V8 | 10 | 13 |
| 8.1L Vortec 8100 V8 | 6 | 9 |
| 6.6L Duramax V8 Turbo Diesel | 8 | 10 |
3rd-Generation GMC Sierra Gas Mileage (GMT900) (2007 to 2013)
| Engine Option | Lowest Combined MPG | Highest Combined MPG |
| 4.3L Vortec 4300 V6 | 15 | 20 |
| 4.8L Vortec 4800 V8 | 14 | 19 |
| 5.3L Vortec 5300 V8 | 15 | 21 |
| 5.3L Vortec 5300 V8 (E-85/Flex-Fuel) | 11 | 16 |
| 6.0L Vortec 6000 V8 | 20 | 23 |
| 6.2L Vortec 6200 V8 | 13 | 18 |
| 6.2L Vortec 6200 V8(E-85/Flex-Fuel) | 9 | 13 |
| 6.6L Duramax V8 Turbo Diesel | 12.2 (Lowest Average) | 15.1 (Highest Average) |
4th-Generation GMC Sierra Gas Mileage (GMT K2XX) (2014 to 2018)
| Engine Option | Lowest Combined MPG | Highest Combined MPG |
| 4.3L Ecotec3 V6 | 18 | 23 |
| 4.3L Ecotec3 V6(E-85/Flex-Fuel) | 12 | 16 |
| 5.3L Ecotec3 V8 | 15 | 19 |
| 6.2L Ecotec3 V8 | 11 | 15 |
| 6.0L Vortec 6000 V8 | 13 | 17 |
| 6.6L Duramax V8 Turbo Diesel | 11.8 (Lowest Average) | 15.3 (Highest Average) |
5th-Generation GMC Sierra Gas Mileage (GMT T1XX) (2019 to 2023/Present)
| Engine Option | Lowest Combined MPG | Highest Combined MPG |
| 2.7L Inline-4 (I4) Turbo | 20 | 23 |
| 4.3L Ecotec3 V6 | 15 | 19 |
| 5.3L Ecotec3 V8 | 14 | 18 |
| 5.3L Ecotec3 V8(E-85/Flex-Fuel) | 11 | 15 |
| 6.2L Ecotec3 V8 | 16 | 20 |
| 3.0L Duramax Inline-6 (I6) Turbo Diesel | 21 | 26 |
| 6.6L Duramax V8 Turbo Diesel | 11.2 (Lowest Average) | 14.9 (Highest Average) |
Frequently Asked Questions (FAQs)
What if I hear a knocking noise from the engine after refueling?
If you hear a knocking noise from the engine after refueling, you may have put in the wrong fuel type, or the fuel is contaminated.
To rule out other causes of engine knock such as improper ignition timing or incorrect air-fuel ratio, be sure to take your vehicle to a mechanic for a proper diagnosis.
What’s the gas tank size of a GMC Sierra?
The GMC Sierra’s gas tank size/capacity starts from 22 to 63.5 US gallons (83.3 to 240.2 liters) for single-tank models and 41 to 63.5 US gallons (155.2 to 240.4 liters) for dual-tank models.
The GMC Sierra’s exact gas tank size is dependent on the generation, series, and trim level of the model.
Do take note that the usage of the terms “bed” and “box” in the GMC Sierra trims below refer to the same thing, which is the open area at the back of the truck used for carrying cargo.
| GMC Sierra Generation/Model Years | Series/Trim | Gas Tank Size/Capacity (US Gallon/Liter) |
| 1st Generation (GMT400)(1988 to 1998) | 1500 Series (6.5-ft Bed) | 25 gal (94.6 l) |
| 1500 Series (8-ft Bed) | 34 gal (128.7 l) | |
| 2500 Series | 34 gal (128.7 l) | |
| 3500 Series | 34 gal (128.7 l) | |
| 2nd Generation (GMT800)(1999 to 2006) | Short Bed | 26 gal (98.4 l) |
| Standard Bed | 26 gal (98.4 l) | |
| Long Bed | 34 gal (128.7 l) | |
| Chassis Cab | 23 gal (87.1 l) | |
| Chassis Cab(Dual Gas Tanks) | 23-gal front tank (87 l) 18-gal rear tank (68.1 l) | |
| Chassis Cab(Deleted Box) | 34 gal (128.7 l) | |
| 3500 Series Chassis Cab | 27 gal (102.2 l) | |
| 3500 Series Chassis Cab(Dual Gas Tanks) | 27-gal front tank (102.2 l) 23-gal rear tank (87 l) | |
| 3500 Series Chassis Cab (California Spec) (Dual Gas Tanks) | 24-gal front tank (91 l) 23-gal rear tank (87 l) | |
| 3rd Generation (GMT900)(2007 to 2013) | 1500 Series Short Box | 26 gal (98.4 l) |
| 1500 Series Standard Box | 26 gal (98.4 l) | |
| 1500 Series Long Box | 34 gal (128.7 l) | |
| 2500 Series Standard Box | 26 gal (98.4 l) | |
| 2500 Series Long Box | 34 gal (128.7 l) | |
| 3500 Series Long Box | 34 gal (128.7 l) | |
| 3500 Series Chassis Cab | 50 gal (189.3 l) | |
| 3500 Series Chassis Cab(Dual Gas Tanks) | 27-gal front tank (102.2 l) 23-gal rear tank (87 l) | |
| 4th Generation (GMT K2XX)(2014 to 2018) | 1500 Series Short Box | 26 gal (98.4 l) |
| 1500 Series Standard Box | 26 gal (98.4 l) | |
| 1500 Series Long Box | 34 gal (128.7 l) | |
| 2500 Series Standard Box | 36 gal (136.3 l) | |
| 2500 Series Long Box | 36 gal (136.3 l) | |
| 3500 Series Standard Box | 36 gal (136.3 l) | |
| 3500 Series Long Box | 36 gal (136.3 l) | |
| 3500 Series Chassis Cab | 63.5 gal (240.4 l) | |
| 3500 Series Chassis Cab(Dual Gas Tanks) | 23.5-gal front tank (89 l) 40-gal rear tank (151.4 l) | |
| 5th Generation (GMT T1XX)(2019 to 2023/Present) | Short Box (5.8 ft) | 24 gal (91 l) |
| Standard Box (6.6 ft) | 24 gal (91 l) | |
| Long Box (8 ft) | 28.3 gal (107 l) | |
| 2WD Diesel Models | 22 gal (83.3 l) |
How much does it cost to fill up a GMC Sierra?
GMC Sierra models with the smallest gas tank size (22 gal for 2WD Diesel) will cost $99.7 to fill up at $4.534/gal (US average diesel price).
GMC Sierra models with the largest gas tank size (63.5 gal) will cost $217.3 to fill up at $3.422/gal (US average regular gas price).
