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The History of the Jeep 4.0 Liter Motor Engine

Jeep enthusiasts disagree on a lot. CJ-7 or CJ-8? Grand Cherokee or Wrangler? Rock-crawling or trail runs? Depending on who you ask about preferences, you’ll get wildly different answers. However, one thing all of us can agree on is the fact that the Jeep 4.0 engine is downright legendary. The 4.0 liter Jeep engine was used in Jeeps from 1987 to 2006 and it’ll never be gone from our hearts. However, the origins of the Jeep inline 6 date back even further. Let’s take a ride down memory lane and look at the history of the renowned 4.0 Jeep motor.

Pre-Jeep AMC Origins

AMC used inline 6 cylinder engines for decades. The modern inline 6 started in 1964 and was known as the “Torque Command.” These engines were found in the famed Rambler Classic Typhoon, which featured distinctive yellow paint and a classic black hardtop. Other cars that were equipped with this engine include the Rambler Classic, Rambler American, AMC Gremlin, and AMC Hornet.

1972 to 1986

The inline 6 underwent a lot of changes over the years, but 1972 saw some of the most prominent ones. For example, AMC changed the bell housing bolt pattern to match the ones used on its V8 engines. This was the first year an inline 6 was featured in a Jeep–the Jeep CJ, to be precise. From then through 1986, the inline 6 was found in many Jeep models, including the Cherokee, Wagoneer, J-Series, and Commando.

Introduction of the 4.0

The Jeep 4.0 oil capacity engine we know and love was introduced in 1986 for 1987 models. AMC developed this 242 cu engine in 26 months with an improved combustion chamber, cam profile, port setup, and overall strength. The engine was so beloved that Chrysler kept it when it took over AMC in 1987. Once Chrysler got ahold of it, it made continuous refinements, most notably reducing vibration, noise, and harshness. It was used in the following Jeeps:

  • Jeep Cherokee: 1987-2001
  • Jeep Comanche: 1987-1992
  • Jeep Wagoneer: 1987-1990
  • Jeep Wrangler: 1991-2006
  • Jeep Grand Cherokee: 1993-2004

Since then, it’s been known as one of the best off-road engines in history.

Why It’s So Loved

So why do Jeep enthusiasts love this engine so much? One reason is because of its impressive torque thanks to its long crankshaft. This makes it perfect for overcoming off-road obstacles. It’s also known for making it to 200,000 miles and over with minimal issues. Not to mention that millions of them were produced, making it super easy to find parts for.

Discontinued in 2006

To the dismay of Jeep lovers everywhere, Chrysler discontinued the famous engine in 2006. The 2007 Jeep Wrangler was equipped with the 3.8L OHV V6 designed by Chrysler, mostly used in minivans. A lot of people weren’t pleased with the decision to put a minivan engine in an off-road vehicle.

The 4.0 inline 6 will never be forgotten. It goes down in history as one of the best workhouse engines. If you have a Jeep with this celebrated engine and need parts for it, you can find all the parts you need at 4WD.com.