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Trail Test: 2012 Jeep Wrangler JK

Posted in Features on December 1, 2011
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When the latest Jeep Wrangler debuted in 2006, enthusiasts were quick to embrace it. Wider and more stable than the previous generation, with a suspension design that was as comfortable on pavement as it was capable on the trail, the Wrangler JK was clearly the most streetable bobtail in the history of the Jeep product line, and its nonpareil off-road chops hadn’t been compromised in the slightest.

There was only one key thing missing: namely, power. The kind of usable power that off-road enthusiasts demand when crawling over rocky sluices and stump-riddled logging roads. The kind of low-end torque that was offered in abundance by the previous-generation inline engine, but which was lacking in the JK’s 3.8L V-6. To make matters worse, the 3.8L was mated to a crude-shifting 20-year-old truck transmission that sucked whatever useful power that could be wrung from the engine at lower revs, and the result was a powertrain that felt weak and anemic at trail speeds, that delivered lousy mileage, and left enthusiasts pining for the return of the inline.

That’s all a distant memory now. For 2012, the 3.8L minivan motor has been replaced by the 3.6L Pentastar V-6 engine, which premiered last year as the base V-6 for the Chrysler vehicle line-up. Assembled at Chrysler’s Trenton, Michigan, plant, the aluminum-block DOHC engine is rated at 285 horsepower at 6,400 rpm and 260 lb-ft of torque at 4,800. That’s 75 more horsepower and a 33-percent power boost over the 3.8L’s 210 horsepower, and while the Pentastar’s peak torque output might not sound too impressive, 96 percent of it is available at 2,000 rpm, and much like the old 4.0L, the engine’s torque curve remains relatively flat from two grand up to redline. What’s more, its all-aluminum block is 33 pounds lighter than the engine it replaces, it meets PZEV emissions requirements, and it affords better mileage per gallon to boot — 21 on the highway and 17 around town.

New for 2012, the 285hp 3.6L Pentastar V-6 replaces the 3.8L that formerly inhabited the JK’s engine bay. The new engine not only produces 70 more horsepower than its predecessor, but it’s also 33 pounds lighter, thanks in part to an all-aluminum block and exhaust manifolds that are integrated into the cylinder heads. Note the location of the alternator, high up on the assembly; Jeep engineers relocated as many electrical components upward in the engine bay as they could to give the Wrangler its 30-inch max water-fording depth.

A great engine, however, is only as good at getting power to the wheels as the efficiency of the gearbox that’s backing it, and in that regard, the old OHV 3.8L was hindered by the 42RE four-speed automatic, which wasn’t so great even when new in ’92. Enter the factory-option Daimler-sourced W5A580 electronic five-speed that’s also found in the latest-generation Grand Cherokee. Obviously enough, the A580 is much more technologically refined than its predecessor, with narrower ratio splits translating into greatly reduced torque-converter slip under throttle, smoother acceleration and quicker passing, reduced levels of interior noise, and better fuel mileage to boot. It was also designed to handle the torque and horsepower loads of the 5.7L Hemi V-8, so it should have no problem handling the Pentastar. You also don’t sacrifice much gearing with the automatic; a Rubicon Wrangler equipped with the juice transmission still sports a commendable 59:1 crawl gear.

For those of you who still prefer an old-school “real-man” grindbox - and according to Chrysler take rates, that’s about 20 percent of new JK buyers - the NSG370 six-speed returns as the standard stick. Transfer cases and axle components are mostly carried over as well. Wrangler Sport and Sahara models get the NVG 241 “Command-Trac” part-time two-speed with a 2.72:1 low-range, while the Dana 30 front and 44 rear axles are fitted from the factory with new-for-2012 3.21:1 gears (Why? Better mileage for Wranglers that mostly see pavement and which seldom tow; 3.73:1s are still an option). Rubicon Wranglers come equipped, as before, with the 4:1 Rock-Trac ’case with Dana 44s, electronic lockers a both ends, and standard 4.10:1 cogs.

Also new to the Wrangler for 2012, the W5A580 five-speed automatic is now the JK’s factory juicebox, replacing the crude-shifting 42RE that had been a staple of the Chrysler truck line since 1992. Long admired for its efficiency of operation, the A580 utilizes bearings instead of bushings throughout its internal assembly to reduce friction, and a unique oil-scavenging system that channels spun oil through slots on the sides of the case saves energy and minimizes losses in fluid viscosity due to “trapped” oil. It’s designed as a “fill for life” gearbox, with no maintenance necessary, but Jeep still gives you a dipstick to check for fluid levels whenever you like.

We had a chance recently to spend a day ’wheeling the repowered JK and its big brother, the four-door Unlimited, through the Tillamook National Forest in western Oregon, and as you might expect, the Jeep’s solid axles, driver-actuated lockers, supple coil/link suspension and electronic swaybar disconnect, had no difficulty delivering ample articulation and flex to keep us motoring over logs, boulders, and fender-deep ruts. Where the new powertrain came to the fore was during steep sections of trail, where slow and predictable vehicle speeds are most desired. On uphill sections, where we’d have once needed to mash on the skinny pedal more aggressively than we’d have liked, there was plenty of power at lower revs, which allowed us to feather the throttle more precisely and avoid overloading the drivetrain. Also, the A580’s electronic Range Select allows you to hold any gear you want for as long as you want, and this allowed us to take full advantage of the Pentastar’s generous compression braking on steep downhills. On pavement, of course, the 75 additional horsepower made themselves apparent anytime we needed to merge into highway traffic, and the extra transmission gear all but eliminated the erratic gear-hunting that was a persistent characteristic of the old four-speed.

Completely revamped last year, the Wrangler’s interior receives a few tweaks for 2012, such as an elevated center console with soft-touch plastic armrest, and improved rear visibility thanks to slightly enlargened rear glass. While a Wrangler’s interior is generally not thought of as an ideal test bed for audio gear, the 368-watt, six-speaker Infinity stereo system (standard on Rubicon models) does a really good job at delivering balanced and distortion-free sound levels to all areas of the cab.

Bottom line: with its interior upgraded for 2011 and a brand-new powertrain for ’12, the Wrangler JK is very much now a finished product. It was already the best Jeep ever. And now, it’s been made even better.

Counterpoint By Phil Howell
The much-anticipated 3.6L VVT V-6 is here. Is it the Hemi-beater most said it was going to be? No. In fact, while highway performance is improved, crawling speed performance is about the same as the 3.8L at best.

Jeep-supplied torque graphs don’t tell the truth. They make the 3.6L VVT look like a diesel with a very flat torque curve. It isn’t. The mill feels weak until about 4,000 rpm, when it comes on strong. Freeway cruising will now be fun in a JK, but the new V-6 has very little low-end torque. The high stall speed of the new five-speed automatic’s torque converter bares this out. Go up to a ledge and the JK stops cold, the engine revs, and revs, and finally the Wrangler hooks up and the Jeep pops up to the top.

Is the 2012 JK better than earlier models? Yes. Is it worth spending the extra money for one if you already have a 3.8L JK? Maybe.

We’ll be spending more time with a 2012 Rubicon soon and will let you know how it performs on familiar trails.

2012 Jeep Wrangler Jk Trial Test dyno Chart Photo 33704753 As you can see here, the 3.8L delivers nearly all of its available torque at 2,000 rpm, and maintains a relatively flat torque curve through the remainder of it's powerband. In that respect, it's a great deal like the 4.0L inline engine that jeep aficionados have missed since 2006. An, obviously, the 3.6L offers a great deal more usable horsepower everywhere from idle to redline than the 3.8L

Vehicle make/model: 2012 Jeep Wrangler Rubicon
Base price: $33,570
Engine: 60-degree 24V DOHC V-6
Max hp/torque (lb-ft) @ rpm: 285 @ 6,400/260 @ 4,800
Transmission (tested): WA580 5-spd. automatic
Transfer case: NVG241 Rock-Trac
Low-range ratio: 4.0:1
Frame type: Steel ladder
Axles, f/r: Dana 44, electronic locker/Dana 44, electronic locker
Axle ratio:
Suspension, f/r: Four-link, coil springs, track and stabilizer bars, monotube shocks, electronic swaybar disconnect/Four-link, coil springs, track and stabilizer bars, monotube shocks
Wheels: 17x7.5 cast aluminum
Tires: LT255/75R17 BFGoodrich Mud-Terrain
Steering: Power, recirculating ball
Brakes, f/r: 11.9-in vented disc/12.4-in solid disc
Wheelbase (in): 95.4
Length (in): 152.8
Width (in): 73.7
Height (in): 71.9
Track, f/r (in): 61.9/61.9
Base curb weight (lb): 4,146
Approach/departure angles (deg): 44/40
Minimum ground clearance (in): 10.5
Max fording distance (in): 30
Interior cargo volume (sq ft): 61.2 (rear seats removed)
Payload (lb): 892
GVWR (lb): 5,038
Towing capacity (lb): 2,000
EPA mileage, city/hwy (mpg): 21/17
Fuel capacity (gal): 18.6

Of course, all that extra horsepower doesn’t mean much if you can’t keep the wheels on the ground, and no factory 4x4 does a better job of that on rough, rocky trails than a JK. Oh, and this tester’s Crush Orange paint and body-matching hard-top is a brand-new shade on the Jeep palette; it’s one of eleven colors that are available for 2012.

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