2012 Jeep Wrangler and Wrangler Unlimited transformed by new engine

2012 Jeep Wrangler Rubicon

2012 Jeep Wrangler Rubicon shows off the extreme articulation of its suspension.

It’s seldom that a single part will transform an entire vehicle, but that’s what happened with the 2012 Jeep Wrangler and Wrangler Unlimited. That single part is Chrysler’s new 3.6-liter Pentastar V-6–so OK, it’s a big part with a number of components and subsidiary elements–but it changes the Wrangler from a vehicle that only an off-roading enthusiast could love to (if properly equipped) an SUV that’s suburbs-friendly and does it, of course, without losing any of its backwoods capabilities.

The Pentastar V-6, which replaced a number of aging powerplants across the Chrysler Group, becomes the sole motivator for the 2012 Wrangler with a choice of two transmissions, a first ever five-speed automatic new to the Wrangler, and the existing six-speed manual adapted to the new engine.

The new Pentastar V-6 debuted in 2011 Chrysler Group products and has been adapted to everything from Ram pickups to the Chrysler Town & Country/Dodge Grand Caravan/Volkswagen Routan minivans, assorted cars, and of course the Jeep Grand Cherokee, where it has been roundly praised.

Output varies slightly from application to application, but it’s an extremely adaptable engine. In the Jeep Wrangler, it’s rated at 285 horsepower and 260 lb-ft of torque. That’s an 83 horsepower gain over the 3.8-liter engine used in last year’s Jeep, and torque is up from 237 lb-ft.

The engine’s advantages are more than just output. The 3.6-liter is more than 90 lbs. lighter than the preceding 3.8, and it’s almost four inches shorter. Less weight means less mass to drag about, improving fuel mileage, and the weight all comes off of the front axle, providing better balance.

Jeeper's eye view over the hood of a 2012 Jeep Wrangler Rubicon

Jeeper’s eye view over the hood of a 2012 Jeep Wrangler Rubicon.

With a shorter engine, Jeep engineers had more freedom in arranging things under the hood. It allowed the intake flow to be improved, allowing more power, for example, and the alternator could be moved higher as well, increasing the Wrangler’s fording depth.

A change made to the engine specifically for Jeep is a redesign for the upper and lower oil pan to accommodate “increased grade requirements,” keeping oil around the oil pump pickup for the times when all the driver can see is either sky through the windshield, or dirt inches in front of the Jeeps seven-slotted grille. The entire intake system is unique to the Wrangler. Induction comes through a revised throttle body positioned on the left side of the engine rather than on the right, as in all other applications.

Like other Pentastar V-6 engines, the engine in the Jeep has an exhaust manifold cast into the cylinder head. Equal-length downpipes plus a optimized collector point helps develop midrange torque. The Wrangler’s exhaust also has a new intermediate pipe resonator along with a reduced internal restriction muffler.

Despite the gain in power and torque, the engine is designed to run on regular 87 octane unleaded, a boon not only from the lower fuel price at the pump but also increasing the likelihood of finding adequate octane in sketchy locations.

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John is a veteran auto writer, first published in Custom Rodder magazine in 1980. Since then, he has been published in all the big car magazines, including Car and Driver, Road & Track, Motor Trend, Auto Week, Automobile, plus a variety of others, including but certainly not limited to Automobile Quarterly, Collectible Automobile, and Special Interest Automobiles. John’s work has also been featured in a number of consumer and general interest magazines such as Consumers Digest, Popular Science and others. John has written four books, including a history of the Mazda RX-7 (selling for more out-of-print than it did new), buyers’ guides for Mazda, Datsun/Nissan and Volvo cars, and is co-author of 365 Cars You Must Drive with Motor Trend editor Matt Stone, and his work has been translated into Italian, Estonian, Portuguese, Russian, and Bulgarian. John is recipient of the prestigious Ken Purdy Award for Excellence in Automotive Journalism, awarded by the International Motor Press Association, and the Golden Quill from the Washington Automotive Press Association. John has three adult daughters and has been married for more that four decades to Mary Ann, Distinguished Professor of Mathematics at East Stroudsburg University of Pennsylvania.