2008 GMC Yukon Hybrid review:

2008 GMC Yukon Hybrid

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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.

In sum
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.

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