AMC 4.2L Inline-6 Engine

The AMC 4.2L engine was produced from 1971-1990 and is very similar to the rest of the lineup of AMC inline-6 cylinder engines. These engines are considered to be very reliable, cheap to make, and torquey. It is found in many AMC and Jeep vehicles throughout the years and also found it’s way into some farm vehicles.

The AMC Inline-6 engine dates back as far as 1952, but the more iconic design was developed and released in 1964. Since then, that 3.8L (232 cu in) inline six has been modified throughout the years until 2006, when development of the 4.0L Inline-6 engine came to an end in the Wrangler TJ.

The 4.2L was produced between 1971 and 1990. Just like the other engines in it’s lineup, it was considered reliable and inexpensive to repair. In 1981, the engine had some small changes including an aluminum intake manifold, plastic rocker arm cover, and the crankshaft was redesigned to only have four counterweights instead of twelve, reducing the weight.

This engine was used in a variety of vehicles throughout AMCs lineup – but here are some of the Jeeps you can find it in!

  • 1972-1988 Jeep CJ
  • 1972-1986 Jeep Cherokee SJ and Wagoneer
  • 1971-1988 Jeep J-Series Truck
  • 1987-1990 Jeep Wrangler
  • 1972-1973 Jeep Commando

Oil Types and Capacities

ViscosityAbove 32°F: 10W-30, 10W-40, 20W-40
Above 0°F: 10W-30, 10W-40
Below 0°F: 5W-30
Capacity6 qts
Oil FilterMopar 33004195
WIX 51626
Drain Plug Torque30ft-lbs
YearsHPTQ
1987-90112hp @ 3200rpm210lb-ft @ 2000rpm
1982-1986115hp @ 3200rpm210lb-ft @ 1800rpm
1979-1981110hp @ 3500rpm195lb-ft @ 2000rpm
1972-1978110hp @ 3500rpm195lb-ft @ 2000rpm
1971150hp @ 3800rpm240lb-ft @ 1800rpm

Common Problems

Lifter Tick

Lifter tick is a common issue on these engines. While essentially harmless, many people do not enjoy the sound of the top of the engine slightly ticking when running. Besides replacing rockers and lifters, the only solution I’ve seen to work is to use a zinc additive in your oil or switch to an oil type that includes higher levels of zinc. One of the most recommended oils to use in the 4.2L engine (and 2.5L & 4.0L for that matter) is the Shell Rotella Diesel Engine Oil. The oil works great in the engine and includes lots of Zinc. As a result, this engine oil usually reduces lifter tick.

Modification

The 4.2L engine is essentially a tractor engine, and wasn’t designed to be used for high horsepower or performance applications. This is further indicated by it’s low horsepower numbers, but high low-end torque. Typically, there is not much that can be modified on this engine to significantly increase performance.

This engine is used in another type of engine build though – the Stroker engine. Stroker engines are highly modified, high performance 4.0L engines. Typically, the modifications include using the crank or piston rods from the 4.2L engine.

To learn more about stroker engines, visit the stroker forums here.

Downloads

Engine Overhaul Guide

Engine Removal Guide

Jeep Engines Guide

Engine Spec Sheet

Engine Parts

Engine Fluids

EngineFluid TypeCapacity
AMC 2.5L I4Above 0°F: 10W-30
Below 60°F: 5W-30
4.0 qts
AMC 4.0L I6Above 0°F: 10W-30
Below 32°F: 5W-30
6.0 qts
GM 2.5L I4Above 0°F: 10W-30
Below 0°F: 5W-30
3.0 qts
Renault 2.1Ltbdtbd
VM Motori 2.5Ltbdtbd

Transmission Fluids

TransmissionFluid TypeCapacity
Chrysler A904 3-Speed
Aisin-Warner AW-4 4-Speed
Chrysler 30RH 3-Speed
Borg-Warner T-4 4-Speed ATF Dexron II1.75qts
Aisin-Warner AX4 4-Speed75W-90 GL3 or GL4
10W-30 Motor Oil
2WD: 3.7qts
4WD: 3.5qts
Borg-Warner T-5 5-SpeedATF Dexron II1.75qts
Aisin-Warner AX5 5-Speed75W-90 GL3 or GL4
10W-30 Motor Oil
2WD: 3.7qts
4WD: 3.5qts
Peugeot BA-10/5 5-Speed
Aisin-Warner AX15 5-Speed75W-90 GL3 or GL4
10W-30 Motor Oil
2WD: 3.32qts
4WD: 3.27qts
New Venture Gear NV3550 5-SpeedMopar MT Fluid
SAE 30W Oil
3.3qts

Axle Fluids

AxleFluid TypeCapacity
Dana 3075W-90
75W-140 (towing)
1.26qts
Dana 3575W-90
75W-140 (towing)
1.75qts
Dana 4475W-90
75W-140 (towing)
2.00qts
Chrysler 8.2575W-90
75W-140 (towing)
2.11qts

Transfer Case Fluids

Transfer CaseFluid TypeCapacity
NP207
NP228/229
NP231
NP242

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4.0L

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