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2008 GMC Yukon two-mode hybrid 2WD test drive

A unique piece: the super-sized hybrid

About.com Rating 4 Star Rating

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2008 GMC Yukon two-mode right side

2008 GMC Yukon two-mode Hybrid right side view.

© Adrian Gable

What do the rating stars mean?

SUVs (especially full-size 8-passenger models) have long been stigmatized as inefficient lumbering beasts that are wasteful, and for the most part, unnecessary road hogs. Fair assessment or not, General Motors is attempting to change public perception with the 2008 GMC Yukon two-mode Hybrid. How are they doing so far? Read on to see how this 2WD Summit White tester, priced at $53,235 performed ($50,045 base). EPA estimates: 21/city, 22/highway. Warranty: 3-year/36,000 mile bumper-to-bumper, 5-year/100,000 mile powertrain and 8-year/100,000-mile hybrid powertrain.

Initial Impression

Scott: “I know it’s important to General Motors that its two-mode hybrid package be successful right out of the gate. They’ve spent considerable time, money and effort perfecting the technology in partnership with Chrysler and BMW, so really, all three manufacturers have a stake in seeing the system perform well and gain public acceptance. So, knowing this, I was not at all surprised to see an extra dose of badging and graphics (fairly screaming out: ‘I’m a hybrid!’) splashed on both sides and both ends of the big Yukon. And you know what? I’m OK with that, in fact, I applaud it as long as it’s tastefully done (as in this case it is). It’s good to let the motoring public know that hybrid drivetrain technology is branching out to every vehicle segment. So, I’d driven the Yukon Hybrid and its cousin, the Chevrolet Tahoe Hybrid, (each for about 20 minutes) at a General Motors 2008 model preview event. That was definitely a tease, not nearly long enough to develop any real feelings for either of them, but just enough to whet my appetite for another encounter. Well, this was my chance--would I fall in love or walk away feeling somehow jilted and disillusioned?”

Christine: “After all the hoopla that GM has kicked up on its release of the new 2-mode hybrid system, I was looking forward to some extended time in this large SUV (after our shorty preview event trips). Having had favorable experiences with GM’s other SUVs, I was looking forward to seeing how the Yukon behaved in its hybrid incarnation.”

Continued below...

Look & feel

2008 GMC Yukon two-mode hybrid power mode

The onboard computer completely controls all modes (engine only, electric only, hybrid, charging and Auto Stop) of the hybrid drivetrain.

© Adrian Gable

There is certainly something to be said for the ride comfort afforded by big SUVs. The long wheelbase and big tires absorb bumps, dips and potholes with nary a notice that they even exist. And that’s just how the Yukon behaves. The combination of its comfort tuned suspension and our tester's sumptuous leather upholstered heated seating left us feeling almost coddled.

Of course, it’s a full-size SUV, so gobs of cargo space is a no-brainer. Behind the third row, there’s 16.9 cubic feet. Remove third row seats and open yourself up to a generous 60.3 cubic feet—and for the really big loads, fold down the second row seats for a cargo gobbling 108.9 cubes.

From time to time, we could detect a faint turbine-like sound. The two mode’s drivetrain (in most instances) tends to be very quiet, but on occasion we noticed in all-electric mode (with just a little load), there was a very faint turbine whine. Although it caught Christine off-guard several times thinking there were sirens in the background, it was not disturbing. Depending upon load, engagement of the electric drive motors can be felt—it’s like a very mild shift in a conventional transmission.

If you’re looking for maximum payload and trailering capacity, the two-mode hybrid may not be for you. Though the 2WD model does share a 7100 lb. GVWR rating with the conventional Yukon, it has slightly less payload capacity (1426 lbs.) and trailering capacity—but still a very reasonable 6200 lbs. Overall, the Yukon two-mode is better suited as an economical medium-duty family utility vehicle rather than an all-out workhorse.

Fuel-ability

In daily operation, the Yukon shows that the two-mode engineers really did their homework (for a full description of how the system works, see What is a Two-Mode Hybrid). The unique combination of conventional transmission components and electric drive motors teamed-up within the same housing, work in concert with Active Fuel Management (GM's version of cylinder deactivation) and the hybrid system's sophisticated management algorithm to keep vehicle in the delicate balance of power and economy.

The hybrid system can operate on engine power alone, electric power alone, or a combination of the two. And unique among full hybrid systems is the addition of Active Fuel Management. Under light cruising conditions where the engine and motors are working together, the computer will shut down four cylinders for optimum fuel efficiency. While cylinder deactivation is available on other GM V-8s, what’s innovative here is the ability for the engine to stay in V-4 mode for longer periods while relying on the electric motors to “pick up the slack.”

And while these features return excellent fuel economy, it can be enhanced further by watching the economy gauge, which encourages driver light-footedness. And of course, like all good hybrids should, the Yukon two-mode shuts off the engine whenever the vehicle comes to a stop. Our combined fuel mileage for the week came in very close to the estimated EPA rating of 21 mpg combined. It probably would have been higher had Scott not spent so much time enjoying the vehicle's 367 lb-ft of torque.

When it’s all said & done

2008 GMC Yukon two-mode transmission cutaway

GM's 2-mode hybrid transmission front motor shown in cutaway view.

© Scott Gable

We were happy with the overall ride, handling and cargo capacity of the Yukon. It does exactly what it’s supposed to do, and it does it well, while leaving little room for gripe. But one area where we think it shines above its direct competition (and exponentially so), is in the fuel mileage department. Yes, that’s what the whole hybrid package is supposed to be about, but we were just a little skeptical that a 5600-pound, 6.0-liter V-8 powered 8-passenger vehicle could actually consistently deliver 20+ combined MPG throughout a solid week of daily commutes.

Scott came away particularly impressed with the two-mode transmission's ability to mix conventional fixed gearsets with two electronic variable drive modes that culminates in an extremely fuel efficient 0.5:1 overdrive ratio. The system is so sophisticated and self-regulated that Scott couldn’t “trick” the system into accepting some of his hypermiling tricks. Turns out, he probably would have reduced the system’s overall efficiency had he figured out a way to fool it anyway.

So, the question begs, is the two-mode system worth the extra cost?

Compared to a similarly optioned Yukon SLT, the hybrid system carries a $2820 price premium. Based on 15,000 miles of annual driving, and factoring in the Yukon two-mode's superior fuel economy (over the conventional Yukon's 16 mpg) and a generous $2200 federal tax credit, the hybrid pays for itself in as little as 10 months. That's a quick payback. In the market for a well-equipped Yukon? Then it's a no-brainer.

Page Two: Enviro-meter & Specs

2008 GMC Yukon Hybrid Gallery

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