The 3.7 liter Dodge - Jeep V6 engine, 2001-2009
The 3.7 liter PowerTech V-6 engine is, essentially, the 4.7 V-8 with two fewer cylinders. It replaced the 2.5 liter four-cylinder, as well as the 3.9 liter V6 engine, both used only on Jeeps and trucks. According to Bob Sheaves, the concept originated at AMC, before the company joined Chrysler.
The 3.7’s first use was being the optional engine on the Jeep Liberty, followed quickly by use as the 2002 Dodge Ram's base engine. In both cases, the 3.7 V6 was mated to a five-speed manual transmission or an automatic. It was later attached to a six-speed manual.
“pgcooldad” predicted the production-end date, correctly saying that much of the machinery would go to Trenton North to produce the Pentastar V6.
Producing 210 horsepower at 5,200 rpm, with 235 lb-ft of torque at 4,000 rpm (that's 157 kW and 319 Nm), the 3.7 was more carlike in its power curve than past Jeep and Dodge Ram engines. However, revving for power was also the key to fuel efficiency not just for this engine, but for most new truck and SUV motors.
The 3.7 has a 90 degree V-6 design with cast iron block, compacted graphite bedplate and aluminum cylinder heads with single overhead cams on each bank. A centrally-mounted, gear-driven counter-rotating balance shaft, along with a split-pin crankshaft, reduces vibration.
Like the 4.7 on which it is based, the 3.7 features chain-driven overhead cams to provide long-term durability and reliability. A fabricated tubular camshaft with powder metal lobes helps reduce engine weight.
Unlike many new engines, the 3.7 has only two valves per cylinder - better for low-end torque, but not as good at higher rpms. Since the 3.7 will be in relatively heavy vehicles, that could be a good design choice.
The composite intake manifold has individually tuned runners for improved performance. Runners are shorter than on the 4.7-liter engine, to produce torque and power peaks at higher speeds. The three-piece shell molded plastic manifold provides individual tuned runners for each cylinder. Molded plastic construction provides more air flow than a cast aluminum manifold with the same dimensions because of its smooth inner walls. Lightweight aluminum pistons and precision forged, powder metal connecting rods reduce reciprocating weight, contributing to the engine's high rpm capability.
High air flow was achieved through hundreds of hours of computer simulation used to optimize every aspect of the air flow equation, from the air cleaner inlet to the tail pipe. Splayed valves and large uniform intake ports, made possible by using overhead camshafts, ensure that abundant air flow enters each cylinder in the same way.
Fast-burn combustion extracts more work from a given amount of fuel, increasing efficiency. Spark plug location near the center of the combustion chamber allows rapid combustion without potentially damaging knock. Rapid, complete combustion maximizes the amount of energy in a given amount of fuel that is transferred to the piston as useful work. The engine was designed for Champion copper spark plugs, and reportedly does not work well with platinum plugs. Tester Marc Rozman wrote:
I did the spark plug testing for Champion when they came in; I was doing calibration work for the 3.7 with engineer Brian Crothers, a sharp guy. We installed their instrumented plugs in different heat ranges to determine the appropriate ones to use for production. They thanked us for building an engine that fits their most common spark plug. I am not sure if there were engineering reasons for the use of the copper vs platinum, the engines these days do not wear the plugs out like the older days; cost may have been the major factor. Personally, I had heard that the Champions were not the best, so I used to use the A/C plugs for my tune-ups.
Spark plug evaluation is hard unless you have all the high tech equipment to do an analysis properly. We had Kistler probed cylinder heads, thermocoupled components, and exhaust gas analyzers.
Molded, high temperature gaskets provide lifetime sealing of all structural joints. The drive overhead camshafts uses three chains with an intermediate shaft to provide the necessary speed reduction in a compact package and to ensure reliability. Direct mounting of the alternator, power steering pump and air conditioning compressor on the front cover of the engine provides accurate alignment to minimize belt wear and noise. An automatic tensioner for the single serpentine poly-vee belt makes adjustment unnecessary for the life of the belt.
The exhaust system of the 3.7-liter LEV includes two mini-catalytic converters, one for each cylinder bank in addition to a main under body converter.
In 2005, the 3.7 engine was treated to numerous economy and idle-quality changes, with a new cam profile, lash adjusters, rings, and a 9.7:1 compression ratio.
The 3.7-liter engine was produced at Chrysler's Mack Avenue engine plant in Detroit, Michigan, next to the 4.7-liter engine plant.