The current version of the Jeep Wrangler, known internally as the JK, was a pretty big deal when it debuted in 2006 as an ’07 model. Not only did it offer a complete rethink of the venerable TJ, but it also brought the Wrangler in to the mainstream with its four-door Unlimited model. At the time of the JK introduction we were happy to see a manual transmission, more refinement, and a spacious interior. No longer did you have to choose between your camping gear and your loved ones, and solid axles and a fold down windshield ensured the Jeep Wrangler’s capability and heritage remained intact.
The Jeep Wrangler JK was an instant success as new customers and the aftermarket embraced it, carrying many of the companies who produced aftermarket parts for it during the economic downturn. It has even been said that the Jeep Wrangler JK is the product that saved Jeep, which is the brand that saved Chrysler. If not for the Wrangler JK, the off-pavement enthusiast landscape could look completely different now.
Since its launch, the JK has gone on to dominate every test we have thrown at it, beat sales expectations on a regular basis and lead the renaissance of the Jeep brand. It is a product that carries a lot of weight and responsibility within the walls of the Jeep brand. So how do you make it better without messing up the formula?
At the time of its introduction, we leveled two distinct complaints about the Jeep Wrangler JK, the interior materials were cheap and the engine was underpowered, especially with the antiquated four-speed automatic. For 2011, Jeep answered our interior criticism with a stunning new dash, as well as some NVH improvements. For 2012, the last piece of the puzzle comes in to place as Chrysler’s newest corporate engine, the 3.6L Pentastar V-6, finds a home under the JK’s hood. This is a thoroughly modern mill that is teamed up with a new-to-Wrangler five-speed automatic or the existing six-speed manual transmissions.
Jeep invited us to the California-Nevada border to test the latest Jeep Wrangler on the storied Rubicon Trail and in and around scenic Lake Tahoe. After a few days in the driver’s seat, here is what we found.
The all-aluminum Pentastar V-6 produces 285hp and 260 lb-ft of torque in JK trim, which is an increase of 83 horsepower and 23 lb-ft of torque, or 30 percent for horsepower and nine percent for torque over the outgoing 90-pound-heavier 3.8L V-6. While nine percent may not sound like much, the 3.6L has an impossibly flat curve, which translates into more power over a greater rpm range.
To get an idea of just how much more power the 3.6L makes over the 3.8L, one just needs to take a look at the dyno overlay. The 3.8L hits 200 lb-ft at around 1,900 rpm and carries it to about 5,300 rpm, near its 5,600 rpm redline. With the 3.6L, 200 lb-ft of torque comes in around 1,500 rpm and it never drops below 200 all the way to its 6,500 rpm redline. In fact, the 3.6L hits 250 lb-ft (13 lb-ft more than the 3.8L max) at 2,100 rpm and doesn’t drop below 250 lb-ft until 5,300 rpm. It is real-world power that you can feel and finally the JK feels competent while passing on two-lane roads.
Backing the Pentastar is the same Getrag NSG 370 six-speed manual found behind the 3.8L, marking the Wrangler as Chrysler’s very first use of the Pentastar/manual in a longitudinal arrangement. The six-speed has been updated with a new clutch housing, flywheel, and long travel damper clutch. It still has a 4.46:1 First gear, making the max crawl ratio available from the factory (4.10:1 axle, 4.0:1 transfer case) 73:1, the same as the 2011 manual-equipped Wrangler.
While we are excited that you can still get a manual with the Jeep Wrangler JK, the bigger news is in the optional W5A580 five-speed automatic that is shared with the Grand Cherokee. In addition to an extra cog over the retired 42RLE, the W5A580 has a lower First gear than the 42RLE (3.59:1 vs. 2.84:1), improving the crawl ratio on automatic-equipped Wranglers to an impressive 58.9:1 from 46.6:1. It also now has Electronic Range Select (ERS), allowing the driver to select the appropriate gear for better control over the drivetrain, and the extra gear helps to lower interior noise levels on the highway. While the transmission is designed to be “filled for life” and doesn’t require maintenance in normal operation, the Jeep engineers added a dipstick, knowing that Wrangler owners are more likely to drive in extreme environments and want to know the condition of their transmission fluid.
Together, the new engine and transmissions improve fuel economy across the board by as much as 2 mpg, and for the first time the Jeep Wrangler is capable of 20 mpg on the highway. The lowest rated Wrangler is the Unlimited automatic with an EPA rating of 16 city/20 highway, while the two-door, manual or automatic, is rated at 17 city/21 highway, giving an impressive highway range of over 400 miles on Unlimited models.
Jeep didn’t stop at the driveline to bump up refinement. Optional are automatic climate control, heated seats, and power mirrors (new for 2011), and they improved NVH and interior comfort through improvements in powertrain mounting, noise damping, and a new acoustic engine cover. Other notable highlights are the availability of a body-colored top and flares on Rubicon models and a wider selection of gear ratios, including taller gears for those who don’t plan to wheel or modify their JK. What this means for those of us planning on bigger tires is that if you are presently running 37s and 5.13:1s with your current 3.8L-powered JK, you can probably have the exact same package, but run 4.88:1s in a 2012, which should help fuel economy and pinion strength.
As for the rest of the Jeep Wrangler JK, the chassis is the same fully boxed, high-strength steel frame with seven crossmembers and 10 body mounts on two-doors and eight crossmembers and 12 body mounts on Unlimiteds. Axles are also identical, which means the aftermarket should have no problems adapting current JK upgrades, such as suspension kits, skidplates, gussets, and gears to the ’12 models.
Three new colors join the pallet for 2012: Dozer Yellow (think bulldozer), Deep Molten Red, and Crush Orange in addition to eight other familiar hues.
On the Road
Our drive from Squaw Valley, California, to the trailhead of the Rubicon was a great test of the Pentastar’s tractability. Despite elevations ranging from 6,000 to 8,000 feet, we were instantly impressed with the power output of the 3.6L. We never found it running out of breath, even as it approached its redline. While the Pentastar doesn’t quite offer up Hemi power, it is a considerable improvement over the 3.8L, and you are no longer left longing for a V-8 in daily driving. Our only complaint, and it is a minor one, is that the 3.6L feels slightly flat pulling off the line when compared to the 3.8L (see sidebar), but once you get above 1,400 rpm it’s all Pentastar. The engine pulls hard and sounds good doing it with none of the harshness associated with the 3.8L.
We found the manual-equipped models to be quite a bit of fun to drive on the asphalt, and the Pentastar even doles out enough pop to get that elusive (to Wrangler, anyway) tire chirp on the 1-2 shift. While the clutch travel is long, the trans shifts smoothly and it is still our choice for those who want more control or an engaged driving experience. Just as in the current Wrangler, we did notice a bit of the gear noise in the 3-4 gate, which is not surprising considering that the Wrangler interior noise levels are down and the gearbox hasn’t changed.
As fun as the manual is, the real treat is going to be for those new buyers who currently drive an automatic JK. The 3.6L/five-speed automatic package is a substantial upgrade over the 3.8L/four-speed combo. No longer does the driveline feign power with noise or reluctantly shift at its leisure. With a wide powerband and a well-matched transmission, the ’12 Wrangler feels light on its feet and shifts are appropriate and well timed. Our favorite feature of the new transmission is ERS. Select a gear and the transmission will hold it all the way to the fuel cutoff at redline, never second-guessing your selection by upshifting on its own.
Out on the road it is clear that this is the quietest Wrangler ever. While NVH improvements are noticeable and appreciated, old-schoolers mustn’t worry because the upright windshield still makes plenty of wind noise on the highway—you’ll never feel too far removed from a traditional Wrangler experience. Want more? Just drop the top or pop off the front panels for more wind in the hair.
On the Trail
Jeep quotes the water fording depth of the Wrangler Rubicon at 30 inches, which came in handy as the Rubicon Trail was often underwater due to a particularly wet winter season. With the 4.0:1 transfer cases churning away under our Rubicon testers, we have to be honest when we tell you that the ’12s weren’t much different on the trail than the ’11s. And that is probably a good thing. The 3.6Ls performed flawlessly on the Rubicon and you wouldn’t know much has changed, which should make the purists happy.
We’d say the biggest change is from automatic-equipped models where we had the ability to lock in First via ERS and enjoy the improved crawl ratio.
No doubt about it, the days of the tractor-like power delivery of the 4.0L straight six are over, but if you are already used to the high-rpm powerband of the 3.8L, you won’t need to adjust your driving habits to adapt to the new engine.
The Pentastar V-6 is a fantastic upgrade that will appeal to majority of Wrangler buyers, especially those who may never have considered a Wrangler before. We wouldn’t be surprised to see the aftermarket coax more than 300 horsepower from this engine in short order and it should serve to increase the Wranglers popularity even further. The bottom line is that as good as the Wrangler is on the trail, this driveline upgrade makes it an even better all-around vehicle in daily use. The 2012 JK is the most versatile Wrangler ever, so if you’ve been waiting to buy one, the time is now.
What’s Hot, What’s Not
Hot: Sweet engine, more fuel efficient, more refinement, same capability
Not: Slightly less low end off idle, and…
Our Take: More of what you want and less of nothing else
Vehicle/model: 2012 Jeep Wrangler Rubicon 2DR
Price as tested: N/A
Engine: 3.6L 60-degree DOHC V-6
Rated hp/torque (lb-ft): 285/260
Transmission(s): NSG 370 6-speed manual/W5A580 5-spd automatic
Transfer case: NV241OR Rock-Trac
4WD system: 2-speed, part-time
Low-range ratio: 4.0:1
Frame type: Fully boxed ladder frame
Suspension, f/r: Live axle four-link w/coil springs and monotube shocks/Live axle four-link w/coil springs and monotube shocks
Axles, f/r: Dana 44, Tru-Lok electronic locker/ Dana 44, Tru-Lok electronic locker
Axle ratio: 4.10:1
Max crawl ratio: 73.0:1
Steering: Power recirculating ball w/ damper
Brakes, f/r: 11.9x1.1-inch vented rotor w/single piston floating caliper/12.44x0.47-inch solid rotor with single piston floating caliper
Wheels (in.): 17x7.5 painted cast aluminum
Tires: LT255/75R17 BFGoodrich Mud-Terrain
Wheelbase (in): 95.4
Length (in): 152.8
Height (in): 70.9 (hardtop)
Base curb weight (lb): 3,760
Approach/departure angles (deg.): 44.3/40.4
Minimum ground clearance (in): 10.2
Payload (lb): 892
Interior cargo volume (cu ft): 61.2
Max towing capacity (lb): 2,000
Fuel capacity (gal): 18.6
Fuel economy (mpg): 17 city/21 highway
Behind the Pentastar
One of the most important products to come out of Chrysler is its next-generation V-6 engine, dubbed the Pentastar. The Pentastar is designed to be compact and lightweight and provides motivation for a variety of vehicles in Chrysler’s portfolio. Currently it is available in everything from the Chrysler 200 to the Jeep Grand Cherokee with plans for it to debut as the base engine in the Ram 1500 next year. The Pentastar V6 was designed to be Chrysler’s engine of the future, meeting all foreseen U.S. and international emissions requirements without the need for an EGR system. The Pentastar V6 is certified to Tier 2 BIN 5 and ULEV II federal standards, as well as PZEV in California.
We had an opportunity to learn more about the Pentastar V-6 and got a lot of insight after our tour of the Trenton Engine Plant during our last visit to Detroit. This nearly 1,000,000 square-foot factory facility was opened in summer 2009 and is packed with state-of-the-art technology and a manufacturing floor so clean you can see your reflection. It has an identical sister facility in Saltillo, Mexico, and at the time of our visit, Trenton employed over 500 people and was on pace to crank out 440,000 Pentastar V-6 engines a year, with plans to increase that total to 500,000.
At the foundation of the 60-degree Pentastar V6 is a high-pressure die cast aluminum block with cast-iron bore liner and aluminum cylinder heads. Bore and stroke are 96mm x 83mm with cast aluminum pistons sporting low friction rings and forged steel connecting rods. The crank is made from nodular iron and features four-bolt main bearings. Two additional bolts are cross-fitted in the main bearing caps to provide a very rigid bottom end. A structural windage tray helps to reduce oil splash on the crank and help bottom end strength.
Cylinder heads are made from 319 T7 heat-treated aluminum and have dual overhead camshafts with roller finger followers and independent cam phasing is used on all four camshafts. Compression is 10.2:1 and piston cooling jets help cool the pistons to control temperature and detonation, allowing the V-6 to make its advertised power on 87-octane gasoline. Using a multi-port fuel injection system, the Pentastar breathes through a 74mm throttle bore.
In addition to the aluminum construction, other weight-saving tactics include the absence of exhaust manifolds. Instead of headers, the exhaust passages are cast directly in to the head, eliminating complexities in the exhaust stream and saving space. Equal-length downpipes, are tuned for torque as well. The Pentastar improves NVH and lowers weight even further by eschewing bracketry and having all of the accessories bolted to the engine itself.
The overall length of the Pentastar V6 engine is only 19.8 inches long, more than 3.5 inches shorter than the 3.8L V-6 it is replacing in the Wrangler. Because it is so much more compact than the 3.8L, it allowed engineers to maximize intake airflow for more power. Wrangler has a unique intake manifold tuned for midrange torque and is the only Pentastar engine with the throttle body on the left side of the engine. Other Wrangler-specific changes include a unique oil pan arrangement to keep the engine oil within reach of the oil pump to prevent oil starving at extreme angles. To keep the alternator out of harm’s way, it is mounted high on the engine for maximum water fording ability. Wrangler also gets a 600-watt pulse-width-modulated fan for improved cooling performance and a full-face A/C condenser that is 20 percent larger.
To ensure quality, reliability, and durability, the Pentastar design went through 45,000 hours of computer analysis before the first engine block was cast. Once the engines were produced, they logged 12 million customer equivalent miles on the dyno and millions of actual field-testing miles. For easier service, oil change intervals are 8,000 miles and utilize a paper filter mounted in a canister on top of the engine.
The current 3.6L displacement is just the tip of the iceberg of the Pentastar’s potential. Its displacement can be scaled down to as little as 2.7L or up as high as 4.0L and it is also designed to work with a wide range of technologies such as direct injection, Fiat’s Multi-Air system, or turbocharging. Come to think of it, we wouldn’t mind a turbocharged 4.0L in our next Wrangler.