Jeep 4.0L: Everything You Need to Know

Typically when you hear someone talk about an impressive inline-six engine, they're referring to the Toyota 2JZ or the Nissan RB26, the Ford Barra, or even the BMW N54/N55. While those engines are awesome and we've made videos about all of them in the past, there's another really awesome inline-6 ​​engine that no one really talks about and that's the Jeep 4-liter. While the 4-liter engine may not have as much performance potential as the other inline-6 ​​engines, it is arguably more reliable than all of them. Warning: This is one of my favorite engines, but I'll try to keep this video as unbiased as possible.

Let's get into it. What's particularly interesting about the four-liter is that its roots date back to 1964 with the AMC Rambler American, which was a small compact car that featured a handful of different engines, one of them being a 232 cubic inch inline. six

know

n as the typhoon 6. While the modern 4-liter doesn't share many things with those older engines, they share a lot of the same architect and those older engines laid the foundation on which the 4-liter was built. Over the years, AMC updated their inline-six engines with different displacements and design features until 1986, when they released the modern 242 cubic inch 4-liter engine.

During the development period the AMC 4-liter wasn't exactly doing incredibly well, so to save development costs on the 4-liter they used many of the same dimensions and architectural features found in older inline-6 ​​engines. of the 232 and 258. family of cubic inches. This is evident by the fact that the 4-liter heads practically bolt onto a 232 or 258 cubic inch AMC inline-6 ​​engine. What's even more interesting is that, according to AMC historian Frank Swigert, sorry if I've butchered your name, it's entirely possible and relatively common to put a 258 cubic inch crank and connecting rods into a 4-liter engine to make an engine. 280 cubic inches.

This can be done with stock 258 cubic inch crank and connecting rods and a 4 liter block and pistons. Before we get into the details, I want to cover some really basic information for those of you who are completely new to this engine. As the name suggests, the 4-liter is a 4-liter inline-6. It features a cast iron block, a cast iron head, 2 valves per cylinder, and lacks any type of variable valve timing or variable valve lift. The diameter measures 98.4 millimeters and the stroke is 86.7 millimeters, which is equivalent to 3962 cc of displacement that is rounded to 4 liters. Depending on the year of the engine, the compression ratio can vary from 8.8 to 1 all the way up to 9.2 to 1.

Now, something that's really interesting about this engine, which is very different than any other inline 6 engine we've featured in this channel is that this The engine does not use overhead camshaft. What I mean by this is that there is no camshaft above the cylinder head. Instead, the 4-liter uses a single cam in the block with hydraulic lifters, pushrods, and roller rockers to operate the valves. Another thing that is very different than any other inline six we feature on this channel is the fact that the intake and exhaust ports are on the same side of the head.

Now, normally the air will come in through one side of the head and then the exhaust will come out through the other side of the head; On the 4 liter

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, the air comes in on one side and then the exhaust comes out on the exact same side and the ports alternate. As you can probably imagine, placing the intake ports and exhaust ports directly next to each other on a cylinder head is not particularly thermally efficient, which is probably why you don't see this layout on modern engines. Again, this is very different than any other modern inline-six engine, where you will typically find one or two camshafts on top of the cylinder head, as well as intake and exhaust ports that are opposite each other.

Again, this just shows how old the 4L Jeep really is and how old those internal design features are. Now, something else that you might find really interesting is that you may have noticed that the bore and stroke are actually a little strange for a truck or SUV engine. Typically you'll find a stroke longer than the bore or maybe even just a square stroke and bore, but on the Jeep, the four-liter bore is actually significantly larger than the stroke. Normally a larger stroke will give you more torque, but in this case a large bore doesn't actually mean no torque.

In fact, the 4-liter engine has really intense torque even with that short stroke. When the 4-liter came on the scene in 1987, it was surprisingly powerful for an engine of that size used in an SUV or truck. At its initial release, it made 173 horsepower and 215 pound-feet of torque, which was quite a bit more than other inline-six engines found in Ford, GM, or Nissan trucks or SUVs. Over the years, Jeep increased the power until the final high-performance version generated a whopping 190 horsepower and 235 pound-feet of torque. Ironically, the 4-liter engine was quite impressive upon its initial release in 1987, but power didn't really increase much until it was discontinued in 2006.

Something that many truck or SUV engines of the era didn't feature was a quality system. fuel injection. Many truck and SUV engines at the time were carbureted or used throttle body injection, but AMC decided to go ahead and send the 4-liter to Reynold Bendix for the fuel management and engine management system. This engine management system later became

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n as the Renix system. It is important to note that the 258 cubic inch carbureted engine was produced alongside the 4 liter and the carbureted engine was used in the YJ Wrangler from 1987 to 1990 until the YJ finally used the 4 liter. The Renix system was very advanced when it first came out and Jeep had a clear advantage over other SUV or truck manufacturers with that system, but since then, the Renix system has become known as an overly complicated and really difficult system to work with because It's not really diagnosed very easily.

What I mean by this is that there are virtually no tools that connect to the Renix system and it stores no codes, which means that if you have an intermittent problem, there is literally no way to know what the problem is. Fortunately, when Chrysler bought AMG in 1987, they realized that the Renix system was kind of garbage and by 1991 they had created their own system. In addition to changing the engine management system in 1991, Chrysler also changed the location of the intake ports to help increase flow, added a larger throttle body, improved the intake and exhaust manifolds, and changed the camshaft. .

The result of all the changes in 1991 was a power increase to 190 horsepower and 225 pound-feet. These engines are now known as high-performance engines and many of the Jeeps using 1991 and later engines have a high-performance badge on the side. From 1991 to 1995 there were virtually no major changes to the 4-liter engine, but in 1995, the cylinder head received some small updates and then in 1996, the engine block was updated with more belts and a bolt belt for added rigidity. In 2000 there were some changes to the cylinder head that were poorly designed and caused cracks in the cylinder head. Not all 2000 and newer cylinder heads have this cracking problem, it's just the heads with the zero three three one on the side.

The design of these heads really isn't bad, but they were molded a little too thin and you will often see cracks between the number three and four cylinders. With that oil/coolant mixture cracking, the head basically

need

s to be replaced because it's junk. By mid-2001, Chrysler had fixed this problem by molding their cylinder heads a little thicker while also using the same design that fixed this cracking problem. Over the years, Jeep and Chrysler made a few other small changes to the 4-liter engine, but for the most part it stayed largely the same, and what's particularly interesting is how closely related the 4-liter inline-6 ​​engine is. liters and the 2.5-liter inline 4 engine. .

In reality, the 4 liter and the 2.5 have exactly the same architecture and practically the same design. In fact, if you were to simply take a 4-liter engine and remove cylinders 3 and 4, you'd pretty much end up with exactly a 2.5-liter inline-four. If we look at some of the common problems you will find with a 4 liter engine, surprisingly there aren't that many problems with the 4 liter engine. As mentioned above, 4 liter Renix's are very difficult to diagnose, later engines supposedly have leaking fuel injectors, rear main seals can leak, as can oil filter adapter seals, cylinder heads. O331 cylinder may crack and oil pumps are damaged.

They are known to occasionally wear out prematurely. That's pretty much it for all the common problems. This engine really has very few common problems and that is mainly due to the fact that it is incredibly simple, it is based on a 1960s engine and has virtually no advanced features, no variable valve timing, no valve lift variable, it has practically nothing advanced. Due to the lack of advanced features, there is very little that can really go wrong in a 4 liter engine and these engines are well known for surviving conditions that would definitely destroy any other engine. Now, in my personal experience, I have had 4 liter engines running on 5 cylinders for long periods of time without problems.

I have run them almost without oil, very well. I have run them well below operating temperature due to the lack of a thermostat. There was even a point where I accidentally made a hole and dented the oil pan and the crankshaft was hitting the oil pan. I was able to get it home, remove the oil pan, remove the dents and re-weld it and the engine ran great and I know these points I just mentioned are anecdotal but in my personal experience these engines are absolutely bulletproof . and destroying one of them is basically impossible. When it comes to performance, it's pretty obvious that the four-liter wasn't designed with performance in mind.

It basically has no performance features and getting more power out of one is a bit difficult, although not impossible. One of the most popular versions you'll see is a 4.7-liter stroker that will increase power to about 210 to 220 horsepower and over 300 pound-feet of torque, but that's about all the performance you'll get. of a four liter atmospheric. Now there are quite a few people who have been turbocharging these engines, which is really interesting because these engines sound really wild when they're turbocharged. There are also some supercharger kits on the market, but again, they don't really increase power much; the most you'll really see from a 4 liter engine with forced induction is 250, maybe 260 horsepower.

They really aren't performance oriented engines and you shouldn't expect to get much power from one. That's pretty much

everything

you

need

to know about the four-liter Jeep. I tried to keep this video as unbiased as possible, but I won't lie, this is one of my favorite motors, for the sole fact that they are practically unbreakable and super reliable, and I've had a lot of hands-on experience. with these engines. The reason I love these motors is the same reason so many other people love them: they are super reliable and almost unbreakable. If there is anything you want to add or anything you think I missed, let me know in the comments below.

Sometimes I miss something important when researching this, so if there's something I missed, please let me know below. While you're there, be sure to hit the "Like" button; It really helps the channel. Make sure to subscribe so you don't miss future videos and let me know what videos you want to see in the future. See you at the next one.