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The Workhorse: A History and Look Inside the Jeep's Legendary 4.0 I6


Jeep 4.0

For Jeep enthusiasts, few engines inspire the same level of reverence as the 4.0 inline-6. Introduced in 1987, this powerplant became synonymous with durability, reliability, and pure Jeep capability. At WikiJeeps, we love everything Jeep, and today, we're diving deep into the history of this iconic engine, exploring its strengths and weaknesses.


A Storied Past: The AMC 258 Takes the Wheel


The 4.0 I6 wasn't entirely new. It was based on the American Motors Corporation (AMC) 258 cubic-inch I6, introduced in 1964. Jeep, acquired by AMC in 1970, recognized the engine's potential and built upon its success. Upgrades included a modern fuel injection system, an improved cooling system, and a higher compression ratio, bumping output to 190 horsepower and 221 lb-ft of torque.


The 4.0L's Strengths: A Master of Off-Road and Towing


The 4.0's reputation wasn't built on brute force, but on its ability to deliver smooth, usable power. Here's what made it a legend:


  • Unmatched Reliability: The design prioritized simplicity and robustness. Cast iron construction and a pushrod valvetrain meant it could handle tough trails and high miles with minimal problems.

  • Torque Monster: With its ample low-end torque, the 4.0 made crawling up hills and tackling rough terrain effortless. It gave Jeeps the pulling power needed for serious off-road adventures.

  • Towing Prowess: Whether it was a trailer full of camping gear or a hefty boat, the 4.0 I6 had the grunt to handle towing duties without breaking a sweat.


The 4.0's Achilles Heel: Facing the Facts


No engine is perfect, and the 4.0 has its shortcomings:

  • Fuel Economy: Compared to modern engines, the 4.0 is thirsty. Expect single-digit fuel economy figures in city driving and low teens on the highway.

  • Emissions: The engine doesn't meet stricter modern emissions standards, leading to its discontinuation in 2006.

  • Power: While ample for its time, the 4.0's horsepower pales in comparison to today's powerful V6 and turbocharged offerings.


The 4.0's Legacy: A Timeless Classic


Despite its limitations, the 4.0 I6 remains a beloved engine. Its simplicity, reliability, and off-road prowess have cemented its place in Jeep history. Even today, enthusiasts seek out Jeep Wranglers and Cherokees equipped with this legendary powerplant.


The Final Drive


The 4.0 I6 is a testament to the idea that an engine can be more than just a source of power. It's a symbol of Jeep's can-do spirit and a reminder that sometimes, the most dependable options come in a timeless, unpretentious package.


At WikiJeeps, we celebrate Jeep's rich heritage, and the 4.0 I6 is a significant part of that story. Whether you're a seasoned off-roader or a Jeep enthusiast just starting out, the legacy of this engine is undeniable.

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