Ah, somebody better tell Chevy that mileage is supposed to get better each subsequent year, not worse. Because the 2021 Silverado with Duramax diesel and four-wheel-drive dropped three miles-per-gallon in Highway driving over 2020. So that diesel and 4WD combo have worse mileage for 2021 than in 2020. But Chevy says nothing has really changed from 2020 (though we wish they would have changed the front end).

So what happened? The two-wheel-drive Duramax Silverado did not change any figures from last year, though it should improve by even a mile or two every year. What’s up with that Chevy? But when you see the numbers for the Silverado Duramax with Four-Wheel-drive the numbers drop from last year. 

2021 Silverado highway mileage drops by three miles-per-gallon

City miles-per-gallon drop by one mpg. Highway mileage drops by three, so the combined miles-per-gallon drop from 25 in 2020 to 24 in 2021. Not a huge amount, but when you factor that Chevy should have been able to slightly improve the mileage, it is not good.

The folks at GM Authority queried Chevy and got this response, “The 4WD 3.0-liter configuration went up in its test weight class, which led to slightly reduced fuel economy to 22 city/26 highway/24 combined. The 2WD configuration remains best-in-class with 23 city/33 highway.” 

Chevy later came back and said that the Silverado that was tested was a “higher-contented truck being tested based on the production schedule.” That means this particular truck had extra features that added weight. Carrying extra weight lowers mileage. Get it?

The weird thing about Chevy’s reason is that manufacturers self-test

The weird thing about that reason is that the manufacturers self-test. The EPA doesn’t do regular testing. It will do a surprise visit to yank a vehicle off of the line to see if the numbers it gets matches the manufacturers. So manufacturers normally test what it thinks will be the most fuel-efficient model. Then, it blankets the entire line with those numbers. And finally, it makes sure to inform you that these are just “estimates.” Real-world driving could net a different result.

If one were to test a lifted Silverado with 38-inch tall tires the mileage would be worse. It comes down to physics. But the problem for manufacturers that choose the path of fewer options for testing is that there can be lawsuits. If the customer’s mileage is way lower than the EPA estimates it can result in court time.

Manufacturers have started to test different optioned vehicles to arrive at more realistic estimates

Manufacturers want to avoid lawsuits, so many have started to test different optioned vehicles to arrive at more realistic estimates.  The initial testing was based on Duramax diesel Silverado pickups with lower-trim options. But consumers instead chose more highly optioned Duramax Silverados. To remain EPA compliant Chevy revisited the higher-trimmed Duramax Silverado and released those numbers, which are lower than in 2020. 

But don’t forget that the EPA estimates are just estimates. Mileage can vary wildly based on driving habits, terrain, whether you haul materials or pull a trailer, and options.