Jeep Six-Cylinder 4-1-1

    The lowdown on all Jeep six-shooters

    Though V-8–equipped and V-8–swapped Jeeps seem to dominate coverage and conversations about Jeep power, the truth is that the vast majority of Jeeps rolled off the assembly line with six-cylinder engines under the hood—there are good reasons for this. Six-cylinder engines offer a reasonable compromise between the raw torque of a V-8 and the fuel economy of a four-cylinder. A six-cylinder engine can get most Jeeps moving with some degree of authority, and many of them offer plenty of torque down low in the rpm range, which is right where it’s needed for off-road use. There has been a bewildering array of six-cylinder engines used under Jeep hoods during the 76 years of production (and counting), and it can be difficult to keep them all straight. We’ve compiled this guide that provides the lowdown on each of them. You’ll learn the good and bad about each one, where they were used, and the feasibility of swapping one somewhere other than where it came from factory. If it had six cylinders and it rolled off the line with a Jeep emblem, you’ll find it here.

    3.6L Pentastar

    The 3.6L V-6 Pentastar was a welcome improvement to the JK when it appeared in 2012 models, both two-door and four-door. Not only did it offer significantly more power than the 3.8L V-6 it replaced, it has also proven to be pretty durable and up to the task of light-to-medium towing when needed. As of this writing there is no “official” word on whether or not the Pentastar will continue with the JL, but it’s a pretty sure thing it will be in the engine bay of the next Wrangler, along with a couple of new engine offerings. It’s a solid, well-respected engine that fits right in off the pavement.

    The Good: Respectable power and torque that does well with larger diameter tires, especially when re-geared. Even light-to-medium trailer towing is possible thanks to the relatively broad powerband.

    The Bad: Finicky electronics that throw codes so often that many JK owners keep a scanner in the glovebox, and clearing codes is sometimes a daily ritual. The greater the modifications, the unhappier the electronic nannies get. Though power is decent, peak power is up high in the rpm range, so the engine tends to be “buzzy.”

    Swap Factor: Poor. The engine management system is extremely complex, and it’s not well suited to being transplanted into other applications. Plus there are other, more powerful, V-6 swap candidates with greater aftermarket support. Most of the time people are swapping these out in favor of a V-8 rather than transplanting them into something else.

    Fun Fact: Chrysler had both forced induction and cylinder deactivation technology in mind when they developed the Pentastar, but neither has yet to be implemented in a production application. However, stop-start technology has reached the Grand Cherokee, and looks like it will be on the JL as well.

    Jeep Models: 2012-current JK Wrangler, 2011-current WKII Grand Cherokee, 2018 JL Wrangler
    Displacement: 3.6L (220 cubic inches)
    Bore: 91mm (3.6 inches)
    Stroke: 83mm (3.3 inches)
    Compression Ratio: 10.2:1
    Block Material: Aluminum
    Head Material: Aluminum
    Horsepower: 275-305
    Torque: 251-268 lb-ft

    3.8L EGH

    For all the praise and fanfare surrounding the release of the JK, the one big bummer was the 3.8L V-6 minivan engine that Chrysler put under the hood. Even worse, they backed it with highly mediocre transmissions. The 3.8L was standard equipment under the hood of JKs from 2007-2011. Though more powerful on paper than the 4.0L it replaced, in the real world it felt lethargic and weak, especially once bigger tires were in the mix. We’ll admit that the engine tends to get a worse rap than it really deserves, mostly because it is chronologically sandwiched between two excellent engines, but in the end it just doesn’t have the stones to live up to what came before or after. The 3.8L is decent as long as you leave it dead-stock; any power-adder is asking for trouble.

    The Good: A relatively simple engine management system. There are only three sensors that will cause the engine to quit running, so field diagnosis and repair is fairly easy.

    The Bad: What little power that’s available is high in the rpm range, so the only way to really get up and go is to keep it matted, which is hard on equipment over time. There have been a disturbing number of engine failures reported, enough to bring overall longevity into question. It’s also clear that they don’t have the durability to withstand hard use. Plus, it’s not a question of if the exhaust manifolds will crack, only when.

    Swap Factor: Non-existent. The engine is not very well liked and therefore not a popular candidate for a transplant. Their lack of low-end torque and overall mediocrity are among the biggest reasons JK Hemi and LS swaps are so popular.

    Fun Fact: The minivan reference is not a joke. The engine was initially developed specifically for front-wheel drive configurations, and Chrysler used this engine, as well as its variants, for nearly 20 years in various front-wheel-drive applications. This makes the selection of the 3.8L for the Wrangler all the more baffling, as it was the only rear-wheel-drive application for the engine.

    Jeep Models: 2007-2011 JK Wrangler
    Displacement: 3.8L (230 cubic inches)
    Bore: 96mm (3.78 inches)
    Stroke: 87mm (3.43 inches)
    Compression Ratio: 9.6:1
    Horsepower: 215
    Torque: 245 lb-ft
    Block Material: Iron
    Head Material: Aluminum

    Photo Credit: FCA

    3.0L EcoDiesel

    The lone diesel in this article, the EcoDiesel made its debut in the Jeep Grand Cherokee and Ram 1500 in 2014. Manufactured by VM Motori, the engine has received a lot of rave reviews and is coveted among diesel enthusiasts, despite the premium that the engine brings to new and used examples. With the decent horsepower and gobs of torque on tap, it’s easy to understand why.

    The Good: Impressive power and torque numbers make the EcoDiesel popular for towing, and the engine also delivers excellent mileage around town.

    The Bad: Though reliable, repair bills are pretty hefty. Because of the premium prices the engines commanded when new, used examples remain much more expensive than gas-powered equivalents.

    Swap Factor: We don’t know anyone that has done a swap with one of these yet, but it’s an interesting proposition. It’s a 60-degree V-6, so it’s fairly compact and would physically fit in a lot of different applications. The biggest hurdle is going to be making the complex engine management system work in a non-stock application, and transmission choices are limited to the automatic that lives behind these engines from the factory. It would be a big job, but potentially worthy of the effort.

    Fun Fact: The engine is produced by Italian manufacturer VM Motori, which at the time of engine development was a joint venture between Fiat and General Motors. Fiat bought out General Motors’ interest in the company in 2013.

    Jeep Models: 2014-current WKII Grand Cherokee
    Displacement: 3.0L (183 cubic inches)
    Bore: 3.27 inches
    Stroke: 3.60 inches
    Compression ratio: 15.5:1
    Block Material: Iron
    Head Material: Aluminum
    Horsepower: 240
    Torque: 420 lb-ft

    3.7L PowerTech

    The Chrysler 3.7L V-6 engine has a somewhat checkered reputation. Essentially a 4.7L V-8 with two cylinders removed, the engine shares the same architecture and many components with its V-8 counterpart (which also has a pretty dubious reputation). Used in 2002-2009 Liberties and 2005-2009 Grand Cherokees, the 3.7L made decent amounts of power and delivered reasonable fuel economy. Though there are plenty of examples that have gone more than 200,000 miles without issue, there are also an uncomfortable number of reports where internal components became external. It’s rare that you’ll find a Liberty with the engine still in place at a self-serve yard, so good used examples are in demand (and that’s not necessarily a good thing).

    The Good: This engine offers fairly good power numbers for a V-6 and has a torque curve that’s a bit flatter than the other V-6 engines in this story. The engine is also fairly compact and lightweight.

    The Bad: They seem to be more susceptible to failure when subjected to hard use or lax maintenance than other engines. There is also virtually no aftermarket support or upgrade parts available for this engine.

    Swap Factor: Non-existent. The engine management system is surprisingly complex, and due mostly to a lack of aftermarket support, there’s not much of a knowledge base surrounding these engines. Though decent, there are other better supported engines that produce more power and therefore make better swap candidates.

    Fun Fact: Unlike most other engines in this list, the 3.7L was used only in Dodge and Jeep truck and SUV applications; it was never in a sedan or minivan.

    Jeep Models: 2002-2011 Liberty, 2005-2010 Grand Cherokee
    Displacement: 3.7L (226 cubic inches)
    Bore: 93mm (3.66 inches)
    Stroke: 91mm (3.57 inches)
    Compression Ratio: 15.5:1
    Horsepower: 210
    Torque: 235 lb-ft
    Block Material: Iron
    Head Material: Aluminum

    Chrysler 4.0L

    Though the 4.0L is the same basic engine as its predecessor (the 4.2L), there are enough differences to merit its own place in this article. Essentially a modernized 4.2L, the 4.0L has a significantly improved head and a highly efficient and reliable fuel injection system. In a nutshell, the engineers at Chrysler took a great engine and made it even better. The power, reliability, and low-end torque of the 4.0L has made it a favorite among Jeep enthusiasts worldwide. In the end it was emissions standards that brought the 4.0L down; despite the move to a distributor-less ignition system and other tricks, it became too difficult to make an engine design dating back to the 1960s adhere to modern emissions regulations.

    The Good: Though there were early Renix-injected 4.0Ls, the MPI system that debuted in 1991 is what made the 4.0L famous. The same low-end torque that made the 4.2L popular is retained, but with the improved power and reliability of fuel injection.

    The Bad: Certain years were susceptible to cracked heads due to a casting flaw, but this usually only develops when the engine is badly overheated. Overheating can also cause heads to warp. Cracked exhaust manifolds are almost a given.

    Swap Factor: Good. The electronics and engine management changed throughout the years, but those changes are well documented and the systems themselves remained remarkably simple. These engines are a great choice for swapping into CJs, YJs, and TJs with four-cylinder engines, especially since the engine compartments were designed to accommodate the long engine. The accessory drive systems are the same between MPI 2.5L engines and 4.0Ls (though the transmission bolt pattern is not), and even the motor mount brackets interchange between 4.0Ls and 4.2Ls. They would not be a good choice for JKs, short-hood CJ-5s, and flatfenders due to their length.

    Fun Fact: It has been our experience that 4.0L power levels can vary significantly, even within the same model year. One rumor we’ve never been able to substantiate is that the factory was aware that 4.0L output could vary quite a bit for a variety of reasons, and as such they would set aside the “hotter” 4.0L engines for use in Cherokees equipped with police packages.

    Jeep Models: 1991-1995 YJ Wrangler, 1997-2006 TJ Wrangler, 1987-2001 XJ Cherokee, 1987-1993 Comanche, 1993-1996 ZJ Grand Cherokee, 1999-2004 WJ Grand Cherokee
    Displacement: 4.0L (242 cubic inches)
    Bore: 98.4mm (3.875 inches)
    Stroke: 86.72-87.31mm (3.414-3.4375 inches)
    Compression Ratio: 8.8:1
    Horsepower: 180-190
    Torque: 225 lb-ft
    Block Material: Iron
    Head Material: Iron

    AMC 258 / 4.2L

    The AMC inline-six is arguably the best engine ever produced by American Motors. They make gobs of torque right off idle, they’re stupid-simple, and they last forever. They also enjoyed a long production run and were used in various Jeep models from the early 1970s to the early 1990s. These and other reasons have made the 258 a favorite among Jeep enthusiasts for decades.

    The Good: They’re nearly bulletproof. Their low-end torque makes them very well suited for trail work, and they have no problem keeping a Jeep at freeway speeds for hundreds of thousands of miles.

    The Bad: They weigh almost as much as a V-8, despite being short two cylinders. Like most inline engines, they don’t like to rev as high as other engines, and the length and height of the engine makes packaging it in other applications difficult.

    Swap Factor: Good. The 258 is an especially good choice in CJ applications that were equipped with anemic four-cylinder engines. Their long production run means they are both plentiful and inexpensive.

    Fun Fact: There was a smaller-displacement 232ci variant that was offered as a base engine in early 1970s CJs, as well as fullsize Jeeps back into the mid-1960s. Also, both the 232 and 258 found their way into some International Harvester products.

    Jeep Models: 1972-1981 CJ-5, 1976-1986 CJ-7, 1981-1986 CJ-8, 1972-1986 FSJ Cherokee and Wagoneer, 1972-1988 J-Series trucks, 1987-1990 YJ Wrangler
    Displacement: 4.2L (258 cubic inches)
    Bore: 95mm (3.75 inches)
    Stroke: 98.9mm (3.895 inches)
    Compression Ratio: 9.2:1
    Horsepower: 110-150
    Torque: 195-210 lb-ft
    Block Material: Iron
    Head Material: Iron

    GM 2.8L

    Jeep aficionados might remember that AMC offered an optional GM-built V-6 engine in early Cherokees and Comanches. Though short-lived, we still occasionally run across one on Craigslist and in junkyards. This 60-degree V-6 wasn’t GM’s finest effort, and the engine’s bolt pattern is different than the standard small-block Chevy and 4.3L pattern, so its GM heritage doesn’t make it any easier to swap with something better. This engine was offered alongside the AMC four-cylinder and actually made seven less horsepower and only marginally more torque. Plagued with emissions-choked electronic carburetors, there simply aren’t many good things to say about this engine other than they tend to last if well cared for and lightly used.

    The Good: Though these engines have a slight reputation for failure, we’ve seen plenty well maintained examples go 200,000 miles or more. These engines do have a small following due to their extensive use in a variety of GM applications, so there is some aftermarket support. GM Performance Parts once offered a 3.4L that was a bolt-in replacement and added almost 50 horsepower. It has since been discontinued, but these crate engines are still out there.

    The Bad: There were never fuel-injected variants in Jeeps, and the smog-choked carburetors offer non-existent performance levels. Its 115 horsepower wasn’t much to get even a lightweight unibody XJ up to freeway speeds with any authority.

    Swap Factor: Non-existent. A modern MPI 2.5L four-cylinder makes more power and would at least bolt to the transmission in place of a 2.8L, but unless a super lightweight drivetrain package is the goal, you’d be better off junking the engine and tranny in favor of a 4.0L, GM 4.3L, or just about any other engine.

    Fun Fact: Released square in the middle of the automotive-malaise era of the 1980s, these engines plagued base model Camaros and Firebirds into the mid 1990s. As noted, due to a strange combination of circumstances these engines share the same transmission bolt pattern as the 2.5L GM and AMC inline four-cylinders.

    Jeep Models: 1984-1986 XJ Cherokee, 1986 MJ Comanche
    Displacement: 2.8L (173 cubic inches)
    Bore: 3.50 inches
    Stroke: 2.99 inches
    Compression Ratio: 8.5:1
    Horsepower: 115
    Torque: 145 lb-ft
    Block Material: Iron
    Head Material: Iron

    225 Dauntless Odd-Fire

    The Buick V-6 is probably the second-most-famous six-cylinder engine to be used in a Jeep, followed by the inline-sixes. First appearing in 1965 CJs, Kaiser bought the tooling from General Motors in 1967, and the engine was then produced in-house until it was replaced by the 232/258 in 1972. The odd-fire designation stems from the crankshaft having only three pins spaced 120 degrees apart, just like a V-8. The result is unevenly spaced firing pulses (90-150-90, and so on) that give the engine a very distinctive growl. The Jeep engines used very heavy flywheels to augment low-end torque and also dampen some of the vibration caused by the odd firing.

    The Good: Gobs of low-end torque and the ability to idle very low thanks to the heavy flywheel. With such a long production run of the entire Buick V-6 engine family, there are a lot of interchangeable components like electronic ignition as well as excellent parts availability for most of the internals.

    The Bad: The odd firing order makes the engine look and feel like its running rough even in perfect tune. Mostly due to age, the odd-fire–specific internal components (such as crankshafts) can be difficult to source.

    Swap Factor: Excellent. A Buick 225 (or its later even-fire 231 variant) is an excellent choice in just about every vintage four-cylinder Jeep application. The standard BOP bolt pattern also opens the door for many other engine and transmission options.

    Fun Fact: AMC shelved the Buick engine in favor of its own engine in 1972. Facing the gas crisis, GM bought the tooling it had sold to Kaiser back from AMC in 1974 and went on to develop the 231 V-6, and later the 3800, which continued well into the 2000s. This makes the Dauntless a part of the most-produced six-cylinder engine family in history.

    Jeep Models: 1966-1971 CJ-5 and CJ-6
    Displacement: 3.68L (225 cubic inches)
    Bore: 3.75 inches
    Stroke: 3.40 inches
    Compression Ratio: 9.0:1
    Horsepower: 160
    Torque: 235
    Block Material: Iron
    Head Material: Iron

    The Oldies

    6-226 Super Hurricane Straight 6
    The earliest six-cylinder engine available in a Jeep, the Super-Hurricane was first seen in 1950 Willys pickup trucks. It was used throughout the 1950s and early 1960s in both wagons and pickups. With a reasonably long production history, the engine has proven to be reliable and adaptable to a variety of purposes. The engine was used in several Willys cars in addition to trucks, though the truck versions reportedly had a lower compression ratio and peak torque came at a lower rpm. The length of the engine did not make it a viable swap candidate into the short noses of CJs, but that’s not to say it didn’t happen a few times over the years.

    Displacement: 226.2 cubic inches
    Bore: 3.94 inches
    Stroke: 4.375 inches
    Compression Ratio: 6.86-7.3:1
    Horsepower: 105-115
    Torque: 190 lb-ft
    Block Material: Iron
    Head Material: Iron

    Kaiser Tornado I6
    Though fairly antiquated today, the Kaiser Tornado was generally considered ahead of its time, in part because it used an overhead cam design while many of its contemporary engines were still flatheads. Indeed, it replaced the flathead Super Hurricane. Used in a variety of pickups and wagons in the early- to mid-1960s, it also made an appearance in their military variants, notably the M-715. Designed to be a low-revving workhorse, the Tornado was usually coupled with gearing best suited to speeds below the limits on most modern freeways, but it delivers plenty of torque for moving heavy loads. Though not a viable swap candidate, there’s no real reason to replace a good-running Tornado unless additional power is the goal.

    Displacement: 230 cubic inches
    Bore: 3.34 inches
    Stroke: 4.38 inches
    Compression Ratio: 7.5-8.5:1
    Horsepower: 133-140
    Torque: 199-210 lb-ft
    Block Material: Iron
    Head Material: Iron

    Honorable Mention

    While we’ve covered the full line of factory sixes, there are a couple engines worth mentioning that make good swap candidates. The Chevy 4.3L V-6 is an excellent candidate for a Jeep transplant; it’s compact, powerful, and well supported by the aftermarket, so swapping is easy. Both TBI and Vortec versions are great choices. Another worthy candidate is the Buick 231 V-6. It shares a transmission bolt pattern with the earlier 225, so factory Jeep transmission combinations bolt to this engine. These engines litter junkyards under the hoods of late-70s to early-80s GM cars, so you can afford to be picky. The best examples are usually carbureted but have HEI ignition; later EFI versions are also viable swap candidates.

    Related Articles