Jeep 4.0 Engine History and Cylinder Heads

Categories: Cylinder Head Tips

Despite being discontinued 16 years ago, the Jeep 4.0 engine is still one of the automotive industry’s most recognized and favored engines to date. Today we’re going to head back in time and discover how this engine came to be, and your options for rebuilding the engine – should you need to.

The Jeep 4.0 engine goes down in history as one of the company’s finest additions to the automotive market. Knowing that its drivers were seeking the biggest adventures, Jeep designed a reliable and powerful engine to accommodate almost any plans. While the Jeep 4.0 was highly praised in the Jeep community after its initial release in 1987, it was further discontinued for a new version in 2006. Despite disappointing many loyal Jeep drivers, the Jeep 4.0 is still recognized as one of the best engines for power and control.

Even though the Jeep 4.0 is no longer manufactured, you can still improve used engines. Before buying new, let us help give you a guide to the engine’s history, specs, reviews, rebuild options, performance upgrades, and everything you should know about replacing the cylinder head on your Jeep 4.0 engine.


The History of the Jeep 4.0 Liter Engine

After 26 months of designing and building, AMC produced a new and improved engine to replace Jeep’s 6-cylinder engines. The Jeep 4.0 engine was first introduced in 1986 and was added to the 1987 models the company was about to release. This 242 cubic inch engine offered an impressive improvement in strength and the combustion chamber in comparison to their previous engines. In 1987, Chrysler took over AMC, but they continued producing this engine due to how popular it was.

Sadly, the engine was discontinued in 2006, with the 2007 Jeep Wrangler using a 3.8L OHV V6 from Chrysler. The Jeep 4.0 engine certainly made a mark on the automotive industry and the engine is still known for its strength and power. The good news is that you can still buy parts for this engine online today, so there is a chance you can extend its life and enjoy using it for years to come.

If you want to learn more about the Jeep 4.0 engine, check out the YouTube video below.



How Long Does the Engine Last?

Typically, the Jeep 4.0 engine can last for about 200,000 miles. However, there are many reports of vehicles lasting up to 400,000 miles without too many major issues. One driver, in particular, has reported his ’95 Jeep Cherokee XJ 4.0L has hit the 500,000-mile mark! Don’t believe us? Check out this YouTube video of driver, Damian L. Smith, hitting the half-million miles mark with his 4.0 engine. Not only is that an impressive feat for an older vehicle, but for any engine to survive that long. The Jeep 4.0 engine is a very reliable and long-lasting engine, but they often require rebuilds when they start to age.


Why Is The Engine So Popular?

You might be wondering why the Jeep 4.0 engine is so popular, and it’s primarily due to its excellent torque. This makes it ideal for off-roading and is the reason that most of these engines easily make it to 200,000 miles without major issues. Due to the many years of production of the Jeep 4.0 engine, you’ll find that it’s very easy to find parts for replacement, which is why it’s still such a well-respected engine to this day.

Want to see if the engine lives up to the hype? Then, you have to take a look at some of the most extreme off-roading stunts a Jeep 4.0 engine can pull off.



Reviews of the Jeep 4.0 Engine

Reviews of the Jeep 4.0 engine often state that it’s one of the best Jeep engines. While it’s a simple engine compared to many on the market, it’s very reliable and has excellent capability when used in 4x4s. Of course, there are always going to be some issues with any engine, and for the Jeep 4.0 engine, the most commonly reported issues include water pump failures and oil leaks. Let’s check out some of the top reviews:

  • BlueJeepster on Wrangler Forum:
    • “Very reliable engine. They leak oil and knock all the time but they keep going. We see them well over 200k at the shop all the time. Most sound like they should blow any minute but they keep going.”
  • Ironhead Jed on Wrangler Forum:
    • “There aren’t too many engines that can stand toe-to-toe with the I6 4.0L when it comes to reliability. It just keeps going and going!”
  • Jarod Bianti on Quora Forum:
    • “The 4.0L straight-six engine is arguably the best engine that the Jeep engineers have ever designed. Made of long-lasting materials, the bore and stroke are over square like most engines. 4.0L engines are easily worked on due to their straight block design and in the latter years of the 87-06 run, the 4.0L high output was the coveted engine to be had amongst Jeepers.”


Can You Rebuild a Jeep 4.0 Engine?

It’s completely possible to rebuild a Jeep 4.0 engine, and this is something that you’ll find many people are doing now that it’s been discontinued for such a long time. The good news is that you can find parts for these engines easily online, making this task something that anyone can consider doing.

Many off-road drivers are looking to increase the torque and horsepower in order to drive on various terrains, which means that they are looking to rebuild the engine. There are many ways to improve the performance with simple modifications to the engine, and by carefully taking this process step by step, you can ensure you have an engine that will serve you well for many more years.

Here is a great tutorial on how you can rebuild a Jeep 4.0 engine.



In What Vehicles Do You Find This Engine?

Over the years, constant improvements were made to the Jeep 4.0 engine. This continual improvement is why it’s been used in so many Jeep vehicles, including:

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


How Do You Replace the Cylinder Heads on a Jeep 4.0 Engine?

The cylinder head on your Jeep 4.0 engine can be replaced without working with a mechanic. If you are looking to take on this task yourself, we recommend checking out this video on YouTube for a step-by-step guide through the process.

The Jeep 4.0 engine is considered a relatively easy engine to switch out the cylinder head-on. To start, you’ll want to pull the manifold and the head. Make sure you clean the surface of the block very well before installing the head and gasket. The gasket needs to be installed dry without any sealer before replacing all of the head bolts and ensuring everything is secure. For more detailed instructions on how to replace the cylinder heads on a Jeep 4.0, you can check out the YouTube video below.



Options for Jeep 4.0 Engine Performance Upgrades

There are multiple exciting options for you when it comes to upgrading the engine performance of your Jeep 4.0 engine. While it’s a powerful engine as standard, you can make a few little tweaks to improve your power by up to 20 hp. The engine has a slight restriction on the intake airflow, so you can work to increase the cold-air intake and improve your fuel economy. Many drivers opt to upgrade to a high-performance cap for their ignition, which improves the top-end power and once again increases the fuel economy slightly.

Changing the header on the engine to one made from thicker stainless steel will help to improve the exhaust system. This adjustment will make the system more efficient and reduce the chance of failure with this part. Finally, adding a high-flowing muffler and tailpipe can help to increase exhaust flow and offer a better driving experience. These are all common upgrades that people are still making to their 4.0 engine and will help you to experience the performance you desire from the engine.

The Jeep 4.0 engine is one of the company’s best additions to the market, and while it has been retired for some time now, many people are still rebuilding these engines and making performance upgrades.

By following step-by-step guides, which are readily available online, you can take on this task yourself and enjoy experiencing the high mileage that these engines are so well known for. It’s a very reliable and sturdy engine that has served drivers well for many years, and one we are sure will remain in circulation for years to come.


Buy Replacement Heads at Clearwater Cylinder Head

With over 50,000 happy clients and 25+ years of business, Clearwater Cylinder Head prioritizes customer satisfaction by selling top-quality cylinder heads for cars, trucks, and boats. We are all about producing a reliable product that is worth your money. Our employees are dedicated to manufacturing, inspecting, restoring, and replacing cylinder heads on all vehicles. If you are looking for a replacement cylinder head for a Jeep, then Clearwater Cylinder Head is the place to call. Our team is happy to assist you with any questions regarding cylinder head selection.

Please call us to inquire about new cylinder heads for your vehicle by calling us toll-free at 1-800-572-1963. We look forward to serving you!