The 4.0L engine is synonymous with a Jeep. The engine is common, they were made by the millions, and for the most part, are known as a reliable engine option for many years.

Why is the inline 6 engine in Jeeps the best?

What makes it best for a Jeep? An inline engine, even a six cylinder, has plenty of torque because of it's long crankshaft. That torque is perfect for operating a vehicle slowly, and over off-road obstacles. Jeep also produced millions of the engines, so they are plentiful and easy to get parts for. Every Jeep mechanic knows their way around one.

The history of the 4.0L Jeep engine

The inline sixes for Jeep started in the AMC years, when they owned the company. AMC made inline sixes for cars from as far back as the 1950s. In 1971 they developed the 258 inline six used in the CJ-series Jeeps, as well as the J-Series trucks and Cherokees. (AMC used it in cars too, including the 4x4 Eagle, Hornets, Pacers, etc.). The 4.0L was introduced to Jeeps around 1986. It's still a descendant of the long line of inline sixes from AMC, and was retained when Chrysler bought Jeep.

2.5L vs. 4.0L Jeep engine and why

It's really hard to compare these two because a 4-cylinder just isn't going to give you the torque that an inline six can easily do (stock wise). With that said, if you're going to go to bigger wheels and tires, you'll need to work around the 2.5L shortcoming with re-gearing and some other mods, to maybe get it where you want it to be. Cruising the highway would be no problem, but climbing up boulders could be an issue. (the 2.5L and 4.0L share a lot of parts, so the 2.5 is basically a shortened 4.0L in some respects). The 2.5L might give you better MPG, but then, this is a Jeep. It's not likely the MPG is a concern or at the top of the list of considerations.

Wrangler TJ 4.0L Tech Engine

Jeep TJ 4.0L Engine
The 4.0L engine was most common in the Wrangler TJ series, from 1997 to 2006. When Jeep went to the JK Wrangler, the 4.0L did not continue, so 2006 was the last year. Some Jeep owners say this was a mistake, to retire such a well known and reliable engine.  But with it's longer size, there are only so many ways you can make it fit in a vehicle's engine bay. A V6 is more compact.

Increase power and efficiency with your 4.0L

The 4.0L is still a popular engine, and fortunately for Jeepers, there are hundreds of aftermarket parts to get even more out of these reliable and high torque engines. From high flow heads, to headers, and even better camshafts, you can get more horsepower and more torque from these tough Jeep engines.

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Don't count the Jeep 4.0L engine out just yet. It's got a lot of 4x4 and off-road fans.