2021 Chevy Silverado Owner Says, “I Used To Get 20-24 MPG Highway, Now I’m Getting 13-16 MPG, I Replaced Spark Plugs, K&N Air Filter, and Changed Oil Every 5K, Any Ideas?”

"My Chevy Silverado's gas mileage has dropped by 30%. I would like to know why," says Austin, a 2021 Chevy Silverado owner.

How many truck owners can relate to his situation?

While researching Chevrolet Silverado gas mileage, I found this interesting post on the 2019-2015 Chevy Silverado Facebook Owners page. Austin Phillips, who owns a 2021 Silverado 1500 pickup with a 5.3-liter V8 engine, says his miles per gallon dropped significantly once he reached 90,000 miles.

Austin says, "I'm curious because lately, I have noticed my 2021 Silverado 5.3L truck gets roughly 13-16 mpg @ 75-80 mph. Sometimes it's lower than that. I have owned the truck since new, and I used to get 20-24 mpg consistently on the same highway drive."

Austin is keen to hear from other Silverado truck owners who may have experienced a similar drop in gas mileage. Your input could be invaluable in solving this issue. 

He says, "I have 129,000 miles on the clock. I've replaced the spark plugs (AC Delco) and put on a new K&N high-flow air filter at 75,000 miles, and I have changed the oil every 5,000 miles religiously. I only use Mobile1 synthetic oil." 

He Has the Same Set Of Wheels and Tires

"I started to notice mpg at around 90,000 miles. The truck has been on the same setup (Wheel 22X12, Tire 305/45R22, Lift 2.5) since around 55,000 miles. Is there anything I should be looking for?"

Comments From Other Truck Owners  

Francisco Rodriguez says, "I'm at 165,000 miles, and I've noticed that my truck feels heavy. A buddy suggested changing the ignition coils. I replaced the wires and spark plugs, but I haven't changed the coils. I'll check whether I have the round or square ones and order all eight. Hopefully, that will make a difference."

Mike Capone says, "Since using winter blend gas, I've noticed a lower range and MPG. In the summer, I've achieved over 420 miles per tank with an average of 19 MPG. However, this winter, my average has dropped to 15 MPG, and I’m getting no more than 370 miles on a tank. I have the 5.3L engine with 34,000 miles on it."

The EPA estimated mileage for the 2021 Chevrolet Silverado 4WD 5.3L with a 10-speed automatic transmission is 16/22 city/highway mpg and 19 combined mpg. 

What grade of unleaded gasoline does Chevrolet recommend?

One possible reason for a drop in Austin's gas mileage could be the type of gas he uses. 

Chevrolet says, "If you have the available 5.3-liter V8 engine or 6.2-liter V8 engine, Chevrolet recommends using mid-grade 89 octane gasoline or higher for optimal performance and fuel efficiency. These powerful V8 engines can also run on regular 87 octane in a pinch."

According to posts on Reddit, other Chevy Silverado owners have experienced a drop in gas mileage. 

One user says, "I live in the city with my Silverado 5.3L 1500, which gets 14 mpg. I don't floor it and mostly ease into the gas. I don't tow anything. When the tank reaches about 1/8 to 1/4 full, I fill it up every 5 to 6 days. Once full, the meter can be inconsistent with the mileage range, usually indicating around mid-300 miles until empty. It never shows 400. I use regular gas."

BlueDogBlackLab says, "My '23 5.3 has a lifetime average of 14.6 mpg with 25,600 miles driven so far. This includes a daily 45-minute commute at 60 mph and driving around a construction project. My 2016 5.3 has an overall average of 15.7 mpg; I recorded 19.7 mpg while driving down I-95 yesterday at 74 mph."

What Can Affect the Silverado's Fuel Mileage?

Key points from Reddit threads about declining MPG in the Silverado 5.3L:

1. Driving style: Aggressive acceleration, frequent braking, and high speeds significantly impact MPG. 
2. Tire pressure: Under-inflated tires increase rolling resistance, lowering fuel efficiency. 
3. Maintenance issues: A dirty air filter, worn spark plugs, or a faulty oxygen sensor can all affect fuel economy. 
4. Seasonal changes: Cold weather and winter blend gas can decrease MPG. 
5. Towing/Hauling: Towing a heavy load will significantly drop your MPG. 
6. Vehicle age: As your car or truck ages, some engine components may wear out slightly, impacting fuel efficiency. 

What Can Silverado Owners Do?

• Check your tire pressure and ensure they are inflated to the manufacturer's recommended level. 
• Inspect your air filter and replace it if it is dirty. 
• Review your driving habits and try to accelerate and brake smoothly, maintaining a consistent speed. 
• Check for any check engine lights and have your vehicle scanned for potential issues. 
• Consider a tune-up if your vehicle is nearing recommended service intervals. 

Jim Butler Chevrolet Says There Are Other Things Truck Owners Can Do

1. Slow Down - Gas mileage decreases at speeds over 50 mph or when accelerating hard. 

2. Use Cruise Control When Appropriate - According to Edmunds.com, using cruise control under appropriate conditions can improve gas mileage by up to 14%. Cruise control is most efficient on flat highways rather than in hilly areas.

3. Drive Smoothly—Try to drive as smoothly as possible. Speedy acceleration, jerky braking, and stop-and-go traffic waste gas. Studies suggest that poor driving habits can affect fuel economy by 15% to 30%. Don't put your pedal to the metal.

4. Reduce Idling Time—Idling uses more fuel than restarting your car, and it emits 80% more pollution than when it is in motion. The next time you come to a stop and are waiting for someone, consider turning off your engine to save fuel.

5. Keep Windows Closed—Aerodynamics plays a major role in your vehicle's fuel efficiency. Even partly opened windows reduce aerodynamics and waste gas due to increased drag. Contrary to popular belief, you'll save more fuel with the windows up and the air conditioner turned on during warm weather.

6. Reduce Extra Weight—Trucks are meant for hauling, but extra weight can reduce fuel economy when used as rolling storage. If you keep extra sports equipment, tools, or other larger, heavier items in your truck that you don't use daily, consider storing them in your garage to save fuel.

Final Thoughts and Questions For Chevy Silverado Owners

Austin has done many of the right things to improve this Silverado's fuel mileage. Unfortunately, after a vehicle has traveled a significant number of miles, its engine becomes less efficient overall. 

However, he's driving on the highway at 80 miles per hour, and no truck gets good gas mileage at those speeds. Slowing down will significantly improve the gas mileage. 

My goal is to share information and solutions to help Silverado owners maintain their pickups at their best. So, let's keep the conversation going and continue to learn from each other's experiences.

How About You?

Do you have any ideas for Austin? If so, please click the red Add New Comment link below.

Check out my Chevy Silverado story titled; I Bought a New Chevy Silverado, 4 Months In, the Bank Wants $35K From Me On My Old Truck, the GMC Dealer Never Paid It Off

I am Denis Flierl, a Senior Torque News Reporter since 2012. My 30+ year tenure in the automotive industry, initially in a consulting role with every major car brand and later as a freelance journalist test-driving new vehicles, has equipped me with a wealth of knowledge. I specialize in reporting the latest automotive news and providing expert analysis on Subaru, which you'll find here, ensuring that you, as a reader, are always well-informed and up-to-date. Follow me on my X SubaruReport, All Subaru, WRXSTI, @DenisFlierl, Facebook, and Instagram.

Photo credit: Denis Flierl