The 2008 GMC Yukon Hybrid is either the first guilt-free full-size SUV or an example of unrestrained excess. The Yukon is big, with three rows of seating and a cliff-like front-end. And it uses one of the bigger engines available in the Yukon line, a 6-liter V-8. But it adds GM's new two-mode hybrid system to give it surprisingly good fuel economy. In city traffic, we're talking close to 20 mpg. Good thing it has all those hybrid labels around the body to fend off public rancor.
The cabin electronics are the same as GM has been offering on its bigger vehicles, with a touch-screen LCD and an easy-to-use tabbed interface for accessing navigation and audio functions. The Yukon Hybrid also gets a decent Bose stereo, but it relies on OnStar for hands-free calling.
Test the tech: Emissions-free cruising
Unlike previous mild-hybrid systems from GM, the GMC Yukon Hybrid's two-mode drivetrain is a full hybrid system, capable of driving the vehicle under electric power only. The driving experience is very similar to that of a Toyota Prius, where the engine will shut off at a stop and initial acceleration is handled by the electric motor. To really test the Yukon Hybrid, we tried to see how long we could drive it before the engine kicked in. Our test drivers, editors Wayne Cunningham and Antuan Goodwin, would have to keep the acceleration very light, as the engine will kick in whenever more than moderate pressure is applied to the gas pedal.
The power-flow animation shows when the battery is being charged, but not the charge level.
The test would also be limited by how much juice the battery held, as the system is designed to turn on the engine whenever the battery gets below a certain charge level. As we went to start our test, we noticed an initial hurdle: there is no gauge on the car to show the available charge on the hybrid battery pack. Before each run, we tried to get it charged up as much as possible by building up some speed then lightly applying the brakes. The Yukon Hybrid uses regenerative braking and we were able to see from the power-flow animation when the battery was being charged.
Goodwin took the first run, stepping up into the high driver's seat and getting behind the wheel of the big truck. From a stop, he put light pressure on the gas pedal and the Yukon edged forward. The tachometer remained in the engine stop position as the vehicle climbed past 10 mph. It cruised down the long straightaway of our test loop, building speed slowly up to 25 mph. With such a big vehicle, it was hard to believe we weren't burning any gas. The first turn on our loop went over a section of unpaved road, which added resistance to the wheels, slowing the car and tempting Goodwin to apply more gas pedal pressure. He eased it up, avoiding an engine start, and the Yukon continued to roll. But he got too greedy on the return straightaway, blipping the gas pedal enough to make the engine kick in. His total electric drive time was 2 minutes, 50 seconds.
This animation meant our test run was done, as the engine has kicked in.
Next up was Cunningham, again getting the big Yukon going slowly at first, keeping acceleration light so that the engine wouldn't kick in. The easy cruise down the first straightaway went by at speeds between 20 and 25 mph, but the resistance of the unpaved turn forced him to apply more pressure to the gas pedal. The Yukon Hybrid kept rolling under electric power, clearing that section and starting up the return straightaway. The car rolled noticeably easier on the pavement, and Cunningham kept light pressure on the gas. Just short of one lap, the engine kicked in, most likely because of a drained battery, finishing off the run at 4 minutes, 33 seconds.
We were impressed that the 5,617-pound Yukon Hybrid could be driven under electric power only for close to 5 minutes. We think it could go even longer if the battery was fully charged.
In the cabin
The cabin of the 2008 GMC Yukon Hybrid differs little from its mundanely-engined model-mates. It comes close to luxury, with leather seats and nice wood trim. Third-row seats are removable, creating a massive cargo area. Although GMC sells base-trim Yukons with standard engines, the Hybrid version comes fully loaded, with a navigation system and Bose audio. The only option on our test car was a power sliding sunroof.
The split screen lets you see the map and audio information, and you only need to touch the tab for the full-size map.
We've seen the Yukon Hybrid's DVD-based navigation system in other GM models. It works very well, but is far from the cutting edge. Its maps are a little rough-looking and it doesn't show traffic information or read out the names of streets. But one of our favorite features is the split screen, showing the map on one side and audio information on the other. Destination entry is somewhat limited, only letting you pick points on the map, select points of interest, or manually enter an address. But the system is also tied in with OnStar, so that when you call the service for directions, the destination will be downloaded to the navigation system. Route guidance works well, with easy-to-read graphics and a good amount of warning time before turns.
The LCD also works as the interface for the audio system. For audio sources, you get an in-dash CD player, XM satellite radio, and an auxiliary audio input. Real iPod integration isn't an option. But this system has one unique trick up its sleeve: it can scan an MP3 CD and let you select music from it with an iPod-like interface. After a CD is scanned, you get to choose from a list of artists, albums, and genres, provided the MP3s have proper ID3 tagging. The only drawbacks to this feature are that it takes a while to scan a CD--up to 5 minutes--and you have to rescan the CD if you eject it then put it back in. We really like the usability of the music selection interfaces, too. The system makes it very easy to choose a category from XM or browse music on a CD. Given the quality of the interface, iPod integration would be really nice.
The interface for XM satellite radio works very well, letting you choose categories by touching the center button.
Music gets played through a nine-speaker Bose audio system, which includes a subwoofer. The sound quality is good, although not remarkable. The system has enough power to fill the large cabin, but it doesn't stand out for clarity or separation. You get typical audio controls for bass, treble, mids, fader, and balance.
Although there is no Bluetooth cell phone integration, the car comes with OnStar, which has a hands-free phone service. We generally prefer cell phone integration so you don't have one number for your car and another for your phone. OnStar also provides its remote assistance services and the new vehicle slowdown service, which can stop the car if a thief is about to make a run from the police in it.
We mentioned the power-flow animations, which show when the battery is being charged and when both the electric motor and engine are powering the wheels. The Yukon Hybrid also comes with a standard back-up camera, necessary in a vehicle of this size. A DVD entertainment system is available.
Under the hood
The power train is the real story in the 2008 GMC Yukon Hybrid. This hybrid system was jointly developed with Mercedes-Benz, BMW, and Chrysler, and we should soon be seeing two-mode hybrid cars from those companies. The base engine is a big 6-liter Vortec V-8, which uses variable valve timing and late opening valves, similar to the Atkinson cycle used on other hybrids, for more efficiency. This engine makes 332 horsepower at 5,100rpm and 367 foot-pounds of torque at 4,100rpm. As another fuel-saving trick, the engine has cylinder deactivation, which can turn off up to four cylinders for low-load driving, such as cruising down the freeway.
This hybrid power management module intelligently determines when to use the electric motors and when to kick in the engine.
The hybrid system itself is built into what GM calls the Electrically Variable Transmission. This transmission incorporates two 60-kilowatt motors powered by a 300-volt nickel metal hydride battery pack. The battery pack gets recharged by the engine and from regenerative braking. The transmission has a continuously variable component, similar to Toyota hybrids, and also four fixed gears, useful for towing. All these power components are tied together by three planetary gearsets and four clutches.
Engineering achievements aside, in normal driving this hybrid power train drives the Yukon under electric power at speeds up to 30 mph, as long as acceleration is light. At a stop, such as in traffic or at a traffic light, the engine turns off, a key fuel-saver considering its size. The engine turns back on easily, without any undue vibration or noise in the cabin, mostly because of the transition from electric to hybrid power. We generally like how this power train operates, as it's a treat to silently glide forward in a 5,617-pound beast. Under hard acceleration we did feel big power fluctuations, with an initial boost followed by a very noticeable lag, then more power.
The hybrid animation shows the car in auto stop mode, where the engine turns off when the car is stopped.
With the transmission in Drive mode, the power train intelligently moves between its continuously variable mode and its fixed gears, opting for the latter when under high loads or during freeway driving, when the electric motors aren't needed. But you can move the shifter over to Manual, and shift through the four fixed gears with a switch. Otherwise, the Yukon Hybrid drives like other SUVs. It's big and not really designed for hard cornering. The suspension is sprung pretty high, designed to carry a lot more weight than we were subjecting it to.
This point of this vehicle is fuel economy, and it does very well considering its size and large displacement engine. The EPA rates it at 21 mpg city and 22 mpg highway, the former number being particularly impressive. We drove it extensively on city streets, with a lot of stops at traffic lights, and watched as the trip computer's average fuel economy rose to 18.5 mpg. Adding on some freeway drive ran our total average mileage up to 19.2 mpg. Although we didn't see it break 20 mpg, we came away impressed, as we've seen plenty of smaller cars do worse in city driving. The Yukon Hybrid's emission rating meets California's minimum LEV II requirement.
We had the two-wheel-drive 2008 GMC Yukon Hybrid, which came loaded with navigation and Bose audio for $50,045. Our only included option was the power sunroof for $995. Along with the car's $900 destination charge, its total comes out to $51,940. An all-wheel-drive version is available for a base price of $53,755. The only competitor in the full-size SUV hybrid class is the Toyota Highlander Hybrid, which can be had in low trim, without much in the way of cabin electronics, for $38,820, or in high trim and fully loaded for $47,335. That price is lower than the Yukon Hybrid's, but the Highlander doesn't feel as brawny.
For our Car Tech ratings, the navigation system and stereo give it an average rating. Navigation isn't particularly advanced, and the one stand-out feature of the stereo is its MP3 CD scanning. We give it a high score for the under-the-hood tech, as GM scores the first use of the two-mode hybrid system, even though it was jointly developed. It also earns a good score for design, buoyed by our appreciation of the music and navigation interface.