It’s been a busy four months since the MT Garage’s 2016 Chevrolet Colorado Z71 Duramax diesel had its low-hanging air dam removed. In the meantime we’ve been racking up the miles and hooking up our Emissions Analytics testing gear to see how removing the air dam effected fuel economy.
Before we get to the numbers, here’s a quick refresher on the air dam: A black plastic air dam that spans the width of the pickup comes affixed beneath the front bumper of every Chevy Colorado, save for the coming Colorado ZR2. It’s designed to boost highway fuel economy, but it does so at the expense of off-road performance. The low-hanging air dam seriously impedes clearance off-road, and it will even scrape the tops of some taller parking blocks.
I covered the air dam removal process in the last long-term update, and soon after removing it, I had a chat with Colorado chief engineer Anita Burke to discuss the benefits of the air dam, what we can expect to experience with the dam off, and the removal process.
In short, Burke said the air dam is the way it is in order to aid the Colorado diesel’s segment-best EPA fuel economy rating of 20/28/23 mpg city/highway/combined.
“It’s a significant benefit to fuel economy,” Burke said over the phone. “It’s one of the things that we focused a lot on as we developed the Colorado, paying attention to how [the air] floats around the fenders, the lamps, the hood, the roof, and that air dam is a key attribute to it, so there will be a notable difference in fuel economy once you remove it.” Pressed on providing a number figure, Burke estimated that highway fuel economy will drop at least 1 mpg on the highway without the air dam.
Although the air dam is designed to be detachable, Burke said that she and her team know that the air dam’s location isn’t ideal for off-road use—the Colorado’s owner’s manual even recommends removing it before heading off-road—and that it’s difficult to remove. “It will, as you know, make contact in certain off-road events. I recognize that it is not the easiest [thing] to remove. It takes a bit of work, but that’s something we obviously are very much aware of for our future.”
My last question for Burke concerned an ominous warning on page 197 of the owner’s manual. Right below a paragraph stating that it might be necessary to remove the air dam for off-road driving, it says, “Caution: Operating the vehicle for extended periods without the front fascia lower air dam installed can cause improper air flow to the engine. Re-attach the front fascia air dam after off-road driving.”
To me, improper airflow to the engine sounds like a recipe for overheating and eventually engine damage, so I asked Burke about it. She said the cooling properties change with the air dam removed (especially on gas-powered Colorado’s with active grille shutters), but she also said she cannot envision a situation in which the Colorado’s engine is harmed with the air dam removed.
With fuel economy king, it’s understandable why Chevy invested so much in making the Colorado as efficient as possible on-road even if it means compromising its abilities off-road. With that in mind, I handed the keys to our Colorado Duramax off to our Emissions Analytics team to see just how efficient the little Chevy truck would be.
Its first test would be completely stock as delivered from the factory with the air dam affixed. Under our Real MPG cycle, our stock diesel Colorado Z71 4×4 achieved an impressive 21.5/31.9/25.2 Real MPG city/highway/combined. Compared to our truck’s 20/28/23 mpg EPA rating, the Real MPG results detail a 7.5 percent increase in the city, 13.9 percent increase on the highway, and an overall 9.5 percent increase on the combined cycle.
Not too shabby.
With the air dam and side steps removed, I handed the keys back to the Emissions Analytics team and eagerly awaited their results. Their testing shows that without the air dam, our Colorado Duramax 4×4 achieved 23.6/30.6/26.3 Real MPG city/highway/combined. Compared to the same truck with the air dam on the Real MPG cycle, that’s a 9.7 percent improvement in the city, a 4.0 percent drop on the highway, and a 4.3 percent improvement overall. Compared to the EPA, our truck—without the air dam—improves 18.0 percent in the city, 9.3 percent on the highway, and 14.3 percent on the combined cycle.
That’s not the result we expected, but perhaps we should have. It’s hard to say with 100 percent certainty, but the city Real MPG improvement might be attributable to less low-speed drag and slightly less weight. The 4.0 percent drop in Real MPG on the highway cycle reflects the greater air drag and nose lift at highway speed—which you certainly feel from behind the wheel as the nose feels less planted than before.
Burke and the Chevy team agreed with the latter interpretation of the results and said in an email that the degradation of highway fuel economy on the Real MPG cycle from 31.9 to 30.6 mpg confirms Burke’s earlier estimates.
Although our Real MPG testing provides another data point versus the EPA, your mileage ultimately might vary. So let’s throw another data point into the mix: observed fuel economy. Over 19,073.5 miles with the air dam attached, we netted 23.30 mpg. In the 6,903.3 miles we’ve covered since removing the air dam, an admittedly much smaller sample size, we’ve achieved 23.13 mpg, which is a statistically insignificant 0.72 percent difference between the two.
Ultimately it seems that there’s little to no price to pay at the pump for removing the air dam, and there’s plenty of capability to gain off-road. As our time with the MT Garage Chevrolet Colorado draws to a close, we’ll keep putting on the miles and see if that remains true.