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Pentastar: the competent do-everything V6

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Chrysler started working on the “Phoenix Engine” around 2004-05. As the project neared completion, Cerberus executives moved to kill the project and use Nissan engines instead; a well-timed leak from Auburn Hills to Allpar.com, showing the promise of the almost-completed powerplant, seems to have kept it alive. The engine, newly renamed to “Pentastar,” finally reached production under Fiat, with hundreds of thousands of the engines per year being made by three different factories at once for a while (Saltillo, Dundee, and Trenton).

Designed to replace every other Mopar V6, it ran on regular fuel in its 3.0 liter, 3.2 liter, and 3.6 liter forms and was hooked up to a wide variety of automatics in front, rear, and all wheel drive vehicles. The transmissions included the Mercedes five-speed, Chrysler four and six speeds (for front drive cars and for rear drive trucks), and ZF eight-speeds and nine-speeds. The Pentastar debuted on the 2011 Chrysler 300, Dodge Challenger, and Dodge Charger, but didn’t really wake up on those cars until it was coupled to the ZF eight-speed automatic on the 2013 300/300C and Charger, then on the 2015 Challenger.

Pentastar V6 head during combustion

A full 90% of torque was available from 1,600 to 6,400 (1,800 to 6,360 on the Challenger) on the original Pentastar 3.6; it was smooth and steady, building power in a linear climb as the revolutions went up, happy to work at quite low revs. With the eight-speed or nine-speed automatic, it happily powered cars at highway speeds at quite low revolutions; without feeling sluggish, the Pentastar returned a reliable 31-34 mpg at 75 mpg in the full size Chrysler 300, for example. People could be forgiven for thinking the 292-hp (in that application) six was actually a V8 engine; after all, it wasn’t that long ago that such power was, at best, unusual coming out of a V6.

Originally, there were three variants of the 3.6, which more planned. These were the 3.0, for cars sold in Europe; the 3.2 liter, for the Jeep Cherokee; and the 3.6 liter, for everything else. The 3.0 disappeared when Chrysler left Europe, the 3.2 when the Jeep Cherokee “KL”  ended in 2013. At the dawn of 2024, two factories were making two versions of the 3.6 liter version—the original and the Pentastar UpGrade (PUG).

3.2 Cherokee Pentastar V6

Ferrari modified the Pentastar for the Maserati Quattroporte and Ghibli; with twin turbos and very exacting machining, its output rose to 404 horsepower. Their inability to squeeze out more power, despite a great deal of added expense, may explain why the pure-Mopar turbo and supercharged versions never made it into production. Maserati eventually moved to “real” Ferrari engines, but the Pentastar stayed on for Dodge, Chrysler, Jeep, and Ram; it was reliable, quiet, and still a good power-and-economy powerplant.

The Pentastar was largely state of the art when it was launched, and won spots on Ward’s Ten Best Engines list for several years. Even its weakest 3.6-liter version was more powerful than any past Chrysler six; it also had better fuel economy, less noise, and easier maintenance.

The Pentastar remains the only gasoline V6 used by Chrysler, Dodge, Jeep, or Ram, and will probably be their last V6.

Pentastar Upgrade (PUG)

The Pentastar UpGrade (PUG) was more expensive to make and harder to repair, but it brought 15% more torque at engine speeds below 3,000 rpm for better drivability and less shifting; gas mileage increased by over 6%. On the Grand Cherokee, horsepower rose from 290 to 295.

The revised engine uses two-speed variable valve lift to cut pumping work at low speeds, for a fuel economy gain of up to 2.7%. A torque-driven cam phasing valve timing system cuts oil demand and increases its range from 50° to 70°, cutting knock during hot starts and increasing the ability to use the stop-start system. The valve timing system was also recalibrated to take advantage of the new intake manifold. The computer looked at the rate of change in the accelerator pedal, making aggressive changes when it sensed “pedal to the metal.”

The upgraded Pentastar (PUG) has cooled exhaust gas recirculation to eliminate knocks; a new intake manifold with longer runners enabled higher torque, and new heads with higher tumble intake ports and shrouded combustion chambers allowed the compression ratio to be boosted from 10.2:1 to 11.3:1. New fuel injectors have eight holes for better atomization.

Internal friction was cut by using HG-R1 on the timing drive guide faces (the first production engine using HG-R1), new valve springs, low-tension piston rings, and piston pins with a diamond-like carbon coating.

Chrysler V6 - PUG

New 100-millijoule high-energy ignition coils with platinum spark plugs extended spark plug life.

Redesigning parts cut the engine weight, despite 13 pounds of added content; the lightest PUG weighed 326 lb (vs the original Pentastar at 330 lb). One strategy was thinner walls on some die-cast components. Windage tray weight was slashed by 19%. The two-piece oil pans were eliminated except on Trail Rated Jeeps. The main bearings and crankshaft pins were trimmed, cutting six pounds and reducing friction.

Roads not taken

These roads not taken were projected in 2006, when the Pentastar was still being developed:

V6 Mopar Pentastar engine

The Pentastar replaced all prior V6 engines, in a phrase-out process with the last survivor, the 3.7, ending production in August 2012. The 4.7 liter V8, which produced similar horsepower (with higher torque), was also dropped. The Pentastar was reportedly cheaper to make than past engines, and was also cheaper than GM’s contemporary (at launch) V6.

Technical details

Pentastar engines have an open deck design, with four oil return holes below the head bolt holes. This made manufacturing cheaper, at the cost of upper cylinder support. Other open deck engines included the aluminum slant six. A turbocharger could be added without changing the deck machining, though this was never implemented. Compared with the 3.6 engine, the 3.2 used lower-friction pistons, narrower sleeves, and smaller journals and main bearings, and different rods, for much less rolling resistance and higher gas mileage. The 3.2 and 3.6 had the same blocks.

A chain drive for the cams replaced the timing belts used on prior Mopar V6 engines; and all the engines used regular 87-octane fuel, while some previous V6 designs had required midgrade.

Chrysler Pentastar V6

There were only two head designs at launch, despite there being four variants (rear drive, all wheel drive, front wheel drive, and Wrangler). There were also only two intake manifolds and one set of internal components, including cam and pistons, according to an SAE article by Paul Weissler. The Challenger’s 305 horsepower, the highest on any Pentastar except for the Ram 1500, was created by a better intake air system, which increased airflow from 214 to 220 g/s. The engine was designed to run on E85 without hurting performance or emissions.

The major innovations were:

Dodge Pentastar engine

Ports and manifolds. The intake valve was a single piece of forged heat resistant (martensitic) steel. Exhaust valves are two-piece designs, with a forged austenitic head welded to a martensitic stem, and both have a nitrided surface treatment to prevent scuffing (except at the tip and lock grooves). Roller rocker arms, pivoting on stationary lash adjusters, activate the valves, which use three bead lock keepers to help rotation and retain the springs.

Timing. The timing drive uses four chains, one of which, with a spring-loaded tensioner, drives the oil pump. The other three drive the camshafts. Primary and secondary camshaft chains use oil pressure controlled chain tensioners; the left secondary uses a ratchet, the right secondary and primary do not. Chain guides and tensioner arms alike are made of glass-filled nylon, with nylon wear faces. The valvetrain uses roller rocker arms with hydraulic lifters. The Pentastar V6 is an interference design; it has valve reliefs but only for clearance under normal conditions.

PUG valves at low lift

Pentastar V6 cylinder heads. Aluminum heads had unique left and right castings and integrated exhaust manifolds. The valves have pressed-in powdered metal guides. Thin-walled spark plug tubes are pressed into place and could easily be damaged by careless mechanics.

Engine block. The high-pressure die cast aluminum block has cut slots between each cylinder and cast steel cylinder liners. Three piston oil cooler jets mounted to the block (each cools two pistons) were attached to the main oil gallery. Four powdered metal main bearing caps are cross-bolted, with directional arrows molded in. The main bearing caps are a cross-bolted, 6-bolt design. Three oil drain back drillings are on each of the cylinder banks, and two knock sensors are in the block valley. The engine accessories are bolted directly to the block, cutting vibration and weight versus using brackets. A tensioner for the serpentine belt maintains tension.

MAP sensor. Instead of a mass airflow (MAF) sensor, Chrysler uses MAP sensors and computer algorithms.

Lubrication

A vane-type variable displacement oil pump adjusts the flow rate and pressure; the computer uses a solenoid to drive the pump into low or high pressure mode. Below 3,500 rpm, the pump conserves energy by using low pressure. A force balance mechanism inside the oil pump adjusts the size of the pumping chambers to alter oil flow, reducing the internal chamber size when the oil is cold, which also saves energy. An internal, mechanical ball-and-spring relief valve dumps oil into the sump when needed, for example in a cold start with high engine speed.

Traditional, non-synthetic motor oil with an ILSAC standard of GF5 was recommended at launch; the standard change interval was then 8,000 miles under normal driving conditions, with this oil.

RWD - Ram V6

The oil pick-up tube is supported at the windage tray. Oil pressure and temperature sensors are on the oil filter housing assembly; the oil cooler (a plate-style coolant to oil heat exchanger) is mounted to the oil filter housing. The Wrangler had specific requirements to keep the oil within reach of the pump when the vehicle operates at steep angles; it also has a higher-mounted alternator for water crossing, and a unique intake.

The nodular iron crankshaft common to all Pentastar engines (as of 2010) has an 83% increase in fatigue strength due to the rolled fillet process. The crankshaft has four bolts on the main bearing supports; two more are cross-fitted in the main bearing caps providing an extremely rigid bottom end. A structural windage tray reduces oil splash on the crankshaft and cuts power losses from the reciprocating assembly, while increasing structural stiffness and lowering engine noise.

V6 engine intake and exhaust

Cylinder heads were made of T7 heat-treated aluminum; intake valve diameters are 39mm with 17 degrees relative to the bore axis. Exhaust valves are 30mm in diameter and canted at 18.8 degrees. Combustion chamber volume is 52.7cc.

Torque actuated cam phasers use the natural action of the valve springs to move into position; their small size allows the camshafts to be spaced very closely together for optimum valve angles and combustion chamber geometry.

at V6 engine factory - valve train exposed

A lightweight composite intake manifold, pioneered on the Neon, feeds into a 74mm throttle bore. Spent gases exit through an integral exhaust manifold that is cast into the cylinder head, cutting weight and bringing a broader range of stoichiometric operation, reducing fuel consumption during mountain grade and trailer tow driving.

Meeting future emission standards does not require Exhaust Gas Recirculation (EGR); on launch it met Federal Tier 2 BIN 5, Ultra-low Emissions Vehicle II, and Euro6 standards.

Other Pentastar V6 engine notes

Spark plugs, good for 80,000 miles, are installed at the end of a tube which is pressed into place and cannot be removed. Cylinders are numbered front to rear; the right bank has pistons 1, 3, and 5, the left 2, 4, and 6, with a 1-2-3-4-5-6 firing order. The serial number is on the left side of the block, at the transmission flange.

The Pentastar reportedly did 7% better in fuel economy than the Nissan engine, for the same power output, when tested against its proposed replacement. The planned MDS (cylinder deactivation) system, never implemented, would have dropped three cylinders at a time when they were not needed.

The 60° engine had a length of 503 mm (94mm shorter than the 3.7 and 34 mm shorter than the 3.5). The bore and stroke were 96mm by 83mm. Pistons have a reduced skirt area to cut weight and friction. Piston cooling jets are fitted to each cylinder, spraying oil onto the piston to prevent detonation, control heat, and allow MDS. The smaller 3.2 liter was created by using thicker cylinder liners, rather than by having smaller bores.

Horsepower and torque improvements

Fully dressed, the new Pentastar V-6 is 94 pounds lighter than the 3.7-liter engine and 42 pounds less than the 3.5-liter. On the Jeep Grand Cherokee, horsepower increased dramatically from 210 horsepower to 290 horsepower (38%). The Charger, Challenger, and 300C gained 42 hp, rising to 292 horsepower. The engine was originally rated at just 280 horsepower; engineer Phil Jansen wrote, “The engine team did a fabulous job of increasing horsepower and delivering added fuel efficiency in the final phase of development.”

Quality and production notes

The die-cast blocks were made in both Mexico and Kokomo. Camshafts used in Trenton were made in Trenton starting in 2012; before then, they were made by a vendor in Mexico. Chrysler re-opened part of the Trenton North plant to make Pentastar parts, taking over from another Mexican supplier. Some of the old 3.7 liter production equipment was moved to Trenton to make the new engines; the millionth Pentastar was made on January 27, 2012. Kokomo made the Ferrari blocks, too, which were machined in a separate area at Trenton (Michigan).

The sand-cast heads are washed and inspected before assembly; one worker wrote, “They use an 80 horsepower motor with a 2,500 psi pump about the size of a small diesel motor. To say they come out clean is a gross understatement. The only ‘dirt’ problems I can remember was, a couple of times, having oil pump relief valves sticking with aluminum chips from the vendor — who had all Hell to pay because of it.”

millionth Pentastar V6 from Trenton Engine

The Trenton Engine South plant which makes the Pentastar has flexible CNC-based machining, volume-bundled parts purchasing, and standardized tooling; many parts were machined in Toledo. Trenton South was the fourth auto manufacturing facilities to receive a LEED rating of any kind, and when first built, the only engine manufacturing facility in the world to achieve LEED Gold. In practical terms Chrysler likely saved $1.25 million per year in energy, cut CO2 emissions by 12,000 metric tons per year (or 1,000 homes worth) and saved 1.5 million gallons of water per year.

David Van Buren wrote that they used “overhead gantry type robots in the machine shop. The whole robot can be easily replaced by unplugging, unbolting it and changing the end of arm tooling with minimal lost production time. My observation of the robots in the machine shop told me they appeared to be all about the same type and size.”

He added, “Each major component has an individual identification number with a stamped on it and a radio frequency tag. They know what time each part went into a particular machine. If there is a problem with a part, it’s easy to find! They know what parts are on what engines!”

Because die-cast blocks can be porous, resulting in leaks, the high-pressure die manufacturing process has a higher scrap rate than sand casting. During the cubing process, parts were tested for leaks and scrapped as needed; they may have all been impregnated with silicone sealer. Allpar’s “atwork” wrote, “After machining at the engine plant, it is possible that more porosity is created. Parts are leak tested at the engine plant as well (and possibly impregnated). The high pressure die cast can cause problems; while allowing better dimensional tolerances than sand or lost foam casting, it is more prone to porosity and therefore leaking. Once the high pressure die cast process is worked out, it is very stable, but this takes a lot of development time.”

One of the first Pentastar engines at Trenton Engine launch event

Another Allpar member confirmed to have worked at Trenton, “Mad Duck,” added:

Leak tests are done with low pressure air, and the leak rate is measured over a given time. Air leaks through smaller paths than oil or antifreeze and water, so this is a tougher test. Silicon impregnation was used at Trenton Engine starting with the 3.5 liter aluminum engine; it may have been used earlier on the aluminum heads of the 2.2 / 2.5 liter engines. It works and has stood up over time. I don’t remember any short or long term problems with this process.

Engine blocks and cylinder heads had freeze plugs partly for cleaning out the metal chips from machining. The dark sides are leaks and noise-vibration-harshness problems; a freeze plug is just like a drum for emitting noise. The Pentastar blocks and cylinder heads have no freeze plugs! No leaks, no noise, but getting them clean of chips is a lot harder.

The parts are now using RFID tags and are marked with build dates and times, and a unique serial number for each major part; they are marked using a unit with a resemblance to a dot-matrix printer.

Repairs

Cylinder head failures (to mid-2013)

In 2011-12, some engines had cylinder head failures due to overheating of the #2 cylinder’s valve seats. The problem was indicated by the “check engine” light. The fix was hardened valve guides and seats, entering production in June 2012. Most affected vehicles were Jeep Wranglers; a service bulletin was issued for Wranglers built before January 24, 2012 (MDH 0124XX) to prevent “false positive” check-engine lights.

A build date of 2062 (the 206th day of 2012) stamped on the cylinder head shows that it is one of the newer types. The part numbers of the new heads are RL141353AC or higher (left side) and RL141352AD (right side). Update: Some 2013 model year vehicles may have the old heads.

Chrysler extended the warranty on the left-side heads of 2011-12 (and some 2013) Pentastar engines; bulletin D-14-12, dated June 10, 2014, tells dealers which vehicles are covered — for ten years or 150,000 miles, whichever comes first. At this point the warranty is over.

Some exhaust cam phasers on the early 2011 engines set a check engine light.

Oil filters

Chrysler changed the oil filters and cap O-rings for the 2014 model year, from 68109834AA to 68191349AA; this coincided with changes to the oil cooler. This may not have been a repair issue but an attempt to commonize parts with the VM diesel. Using the wrong part will cause an oil leak.

Serpentine belt

The serpentine belt on early engines must be carefully routed; the water pump is driven off the back of the belt, so an incorrect routing will result in the pump going backwards. Later models use electrohydraulic pumps in a different location, and then have electric power steering rather than electrohydraulic or hydraulic power steering.

Specifications

The announced output of the 3.6 in the 2025 Ram 1500 is 310 hp.

  HP Lb-ft* MPG**
Dodge Challenger 305 268-270 18/26
Chrysler 300, Dodge Charger 292 @ 6,400 260 19/31
Charger Pursuit 291 @ 6,400 260 @ 4,400 19/26
Caravan, Avenger, old 200 283 @ 6,400 260 17/25
2015-17 Chrysler 200 295 @ 6,350 262 19/29
Grand Cherokee 5-speed 290 @ 6,400 260 16/24
Durango (2014) 290 @ 6,400 260  
Ram 1500 305 @ 6,400 269 @ 4,175 to 18/25
Cherokee AWD (3.2) 271 @ 6,500 239 @ 4,400 22/29
Pacifica 287 262  

* at 4,800 rpm unless otherwise specified
** 2014 unless otherwise noted

Specification Mopar 3.6 liter V6 Engines
Material 60° V6 with deep-skirt aluminum block and heads
Valves Dual overhead cam (DOHC)
Four valves per cylinder with 24 valves
Chain driven
Roller finger followers; hydraulic lash adjusters
Dual independent cam-torque actuated phasers
Measurements Fully metric
Bore x stroke 3.6 liter: 220 cid, 3.78 x 3.27 (96 x 83 mm)*
Fuel injection Returnless, sequential.
Compression 10.2:1 (3.2, 10.7:1)
11.3:1 for PUG
Fluids 6 quarts 5W20 oil
14 quarts antifreeze; regular gas
Regular 87 octane fuel
Firing order 1-2-3-4-5-6; cylinder is #1 in the right bank
Pistons Cast aluminum alloy, 354-364 grams
Intake valve timing Opens at 2° ATDC
Closes at 82° (ABDC) or 262° (ATDC)
260° duration, 128° centerline
Exhaust valve timing Opens 59° (BBDC) or 239° (BTDC)
Closes 12° ATDC
251°, duration, overlap 10°

* 3.2 liter: 198 cid, 3.58 x 3.27 (91 x 83 mm)

Sources: Willem Weertman, Chrysler Engines, SAE; Allpar.com; press kits; conversations.

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