2010 GMC Terrain: Underwhelming MPG
September 09, 2010
Our GMC Terrain has the most economical powertrain combination offered. It's got front-wheel drive and the 2.4-liter Ecotec direct-injected 4-cylinder engine. GM often celebrates its 32-mpg EPA Highway fuel economy rating in ads, but the Terrain's much more relevant EPA Combined rating is 26 mpg.
You've seen our monthly fuel economy logs, and recently we've starting comparing our test vehicle's observed average mpg to their EPA Combined rating.
Most of the time we come within 1 mpg of this figure. Our driver rotation and the varied nature of everyone's commute and weekend activities means that, after several thousand miles, things get nicely randomized. No single commute or driving style dominates the average. The exception here is the high-horsepower machines where the temptation to "leg it" is simply too great.
But the GMC Terrain does not fit the pattern. It's a glaring exception and its observed MPG is way off. In our most recent tally, the Terrain's average fuel consumption over 13,000 miles was 20.5 mpg, a full 5.5 mpg (21%) below its EPA Combined rating. It's best-ever tank of 28.7 mpg trails 3.3 mpg (10%) behind the EPA Highway figure.
This weekend, I decided to see if I could explain this. Surely I could do better. I resolved to drive the Terrain on the highway as much as possible -- we'd use our minivan for in-town errands instead. Furthermore, I'd stay in ECO mode, keep to the right traffic lanes, accelerate as if an egg were under my foot, and, whenever possible, use cruise control once we got up to our target speed of 65 mph.
The result? 24.7 mpg over 380.7 miles. The first 150 miles included our trip to Lake Arrowhead, a 24.6 mpg run. The next 230 miles of level freeway worked out to a nearly-identical 24.8 mpg.
Was this pure freeway cruising? Almost. We did go from point-to-point, but the points are at least 50 freeway miles apart. Home to Grandma's. Home to track-day. Home to work. All of it freeway, except for a mile or two at either end.
This was an 85% highway cycle, if not more. EPA Combined assumes only 55% highway. Based on this and my intentionally timid driving routine, I should have had no trouble eclipsing EPA Combined. I should have gotten closer to EPA Highway. I expected high 20's, at least.
Instead, I'm left with the impression that our 20.5 mpg lifetime average really is a reflection of what owners of the 2010 Terrain 2WD 4-cylinder can expect. That's just what it does in real-world mixed driving.
What's the deal? Maybe it's aerodynamics. The Terrain has a blunt nose, and EPA figures come from indoor dyno testing. Maybe it's small-engine syndrome. In the real world, one sometimes needs to overcome a small engine with deeper throttle inputs. Even when you're driving conservatively you have to stay out of the way and match the speed of traffic when you merge. On a fuel economy dyno, traffic is not sweeping around and crawling up your backside.
Dan Edmunds, Director of Vehicle Testing @ 14,142 miles