GM 2.5L “Iron Duke” Inline-4 Engine

The GM “Iron Duke” engine was built by the Pontiac Motor Division of General Motors from 1977 to 1993. It’s original purpose was to be Pontiac’s new economy car engine, but it was later adapted to be used in many more vehicles.

GM began to sell the engine to AMC starting in the 1980 model year. It was used in the Spirit, Concord, and Eagle model vehicles. It was also used in select Jeep CJ models. It was used in three Jeep models:

  • 1981-1983 CJ-8
  • 1980-1983 CJ-7
  • 1980-1983 CJ-5

Oil Types and Capacities

ViscosityAbove 40°F: 10W-30, 20W-30, 10W-40, 30W, 40W
Above 0°F: 10W-30, 10W-40, 20W
Below 0°F: 5W-20, 5W-30, 10W*
Capacity3 qts (2.8L)
Oil FilterWIX 51040
* Do not operate above speeds of 55 mph with 10W oil
197885hp @ 4400rpm123lb-ft @ 2800rpm
198090hp @ 4000rpm134lb-ft @ 2400rpm
198184hp @ 4000rpm125lb-ft @ 2400rpm

Common Problems

Chipped Timing Tooth

The most common failure point of the 2.5L Iron Duke is the timing gear, which is known to chip a tooth around 80,000 miles. The replacement is laborious and requires the replacement gear to be heat-fitted onto the shaft.


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

Axle Fluids

AxleFluid TypeCapacity
Dana 3075W-90
75W-140 (towing)
Dana 3575W-90
75W-140 (towing)
Dana 4475W-90
75W-140 (towing)
Chrysler 8.2575W-90
75W-140 (towing)

Transfer Case Fluids

Transfer CaseFluid TypeCapacity

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