4.0L-Inline or 3.8L-V6 engine for jeep wrangler?

4.0L-Inline or 3.8L-V6 Engine for Jeep Wrangler, Which is more reliable?

4.0L-Inline or 3.8L-V6 engine for Jeep Wrangler? Here, we are going to compare which is the most reliable engine for Jeep Wrangler. Read out the article thoroughly to clearly understand the best suitable engine for your jeep.

The jeep wrangler first came out of production in 1987 and since then there have been 5 generations of the vehicle. Each generation had different engine models available as explained below. 

First-generation wrangler Civilian jeep (CJ) 

This was in production from 1944 to 1986. It originated as an all-purpose vehicle for the military during WWII. There were a couple of engine trims available for this model. 

  • A 160 horsepower 225cc V6. 
  • An 82 horsepower 2.5-liter Iron duke four-cylinder. 
  • AMC’s 100 horsepower 232 and 150 horsepower 305 V-8. 
  • The CJ7 also came with a rarely used 2.4-liter Isuzu diesel 4 cylinder. 
  • A 5-liter V8 was also an available option for the CJ7. 

Second generation (YJ)

This was in production from 1986-1996. The following engine options were available for this model.

  • The 2.5-liter AMX 150 straight-4 engine is standard. 
  • 4.2-litre AMC 258 straight-six engine. 
  • A fuel-injected 4.0-liter AMC 242. 

Third generation Wrangler (TJ) 

This was in production from 1997-2006 and came with the following available engine options.

  • 2.5-liter straight-four. 
  • 2.4-litre Powertech. 
  • 4.0-litre AMC straight-six.

Fourth-generation wrangler (JK) 

This was in production from 2007-2017. Wranglers from this generation were more technically advanced compared to other generations. Engine options that came with the JK wrangler are as follows. 

  • A 3.8-liter EGH V6 was the base engine in 2007 and was replaced by the 3.6-liter Pentastar V6 on the 2012 models. 
4.0L-Inline or 3.8L-V6 engine for jeep wrangler?

Fifth-generation wrangler (JL)

Production of this model began in 2018 and is still ongoing to date with several available engine trims depending on the year of the model from 2018 forwards. 

  • A 2.0-liter hurricane I4-T.
  • A 2.0-liter hurricane I4-T gasoline hybrid. 
  • A 2.0-liter hurricane I4-T gasoline PHEV 4XE plug-in hybrid. 
  • A 2.2-litre MultiJet 2 I4-T diesel. 
  • A 3.0-liter EcoDiesel V6-T diesel. 
  • A 3.6-litre Pentastar V6 gasoline. 
  •  A 3.6-liter Pentastar V6 gasoline hybrid. 
  • A 6.4-liter Hemi V8 gasoline. 

Here, we are going to discuss two specific engines, The 4.0-liter AMC straight-six and the 3.8-liter EGH V6. 

The 4.0-liter AMC straight-six ***

This engine was introduced in 1986 by AMC and it was so good that when Chrysler took over AMC in 1987, they kept it and made it even better by reducing noises, vibrations and harshness. It was used in some jeeps as listed below.




Jeep Wagoneer


Jeep Comanche


Jeep Cherokee


Jeep Wrangler


Jeep Grand Cherokee

This engine was however only used in the third-generation wrangler (TJ) which was discontinued in 2006 so if you are looking for a jeep with a 4.0 in-line six then the TJ is the vehicle for you. 

As the name suggests, the engine is a 4.0L inline-6. The engine features a cast-iron cylinder head, a heavy cast-iron block with two valves per cylinder.

The engine does not have a variable valve timing or variable valve lift. The displacement in the engine is not four liters, it’s 3962 cubic centimeters which are rounded off to four liters.

This engine has one unique feature that makes it a standout among other inline-six engines, it does not use overhead cams, instead, it uses a single camshaft inside the block which uses hydraulic lifters, pushrods, and rocker arms to operate the valves. 


This engine wasn’t built to be a high-performance engine it was built for reliability and that’s what people love about this engine. It can be pushed deep into the 200k mile range without any or little issues.

Though some tuners have been able to get high amounts of horsepower and torque from this engine it does cost a lot and the reliability of the engine is negatively affected. A stock 4.0-liter AMC makes 173 horsepower at 4500 RPM and gradually rises with increasing RPM to the maximum of 190 horsepower at 4750 RPM and about 320 pound-feet of torque at that same RPM.

The mpg of a wrangler with this engine averaged about 13 mpg city and 17 mpg highway thus a combined average of 15 mpg. This is for the wranglers with a 6-speed manual.

For the ones with a 4-speed automatic, it’s 13 mpg on city and 16 mpg on the highway thus an average of 14.2 mpg. This shows that if you drive the automatic, you’ll spend more money on fuel as compared to someone driving a manual. 

Maintenance and issues in 4.0L-Inline Engine On Jeep Wrangler

This is one of the best engines ever to be put in a vehicle, it has low maintenance costs and can go for miles if maintained well. Modifying the engine, which is not easy, will negatively affect the durability of the engine and increase fuel consumption.

Owners who have not tampered with their engines can testify that the 4.0-liter AMC straight-six is one of the best reliable engines out there. 


  • It’s made of long-lasting materials.
  • Most efficient in the middle and low RPM and has good performance in the high RPM. 
  • Low maintenance costs.


  • A little bit underpowered.

Recommended Maintenance accessories for 4.0 Liter Inline Engine

The 3.8-liter EGH V6

This came up as a continuation of Chrysler’s 3.3-liter V6. It was manufactured in 1991 and a larger bore and new stroke to increase the displacement.

This engine was used in the fourth-generation Wrangler (Jk) until 2007 but as from 2012, it was replaced by the 3.6-liter Chrysler Pentastar V6 engine

When the 3.3-liter V6 was replaced by the 3.8-liter V6 there was an increase in power as time went by and the engine was used in the following vehicles.




Chrysler New Yorker & Chrysler Imperial


Chrysler Minivans


Jeep Wrangler JK


Volkswagen Routan


When this engine was out in a jeep wrangler it produced 199 horsepower and 315 pound-feet of torque at 5000 RPM which is not that bad and came with either a six-speed manual or a four-speed automatic.

Fuel consumption for wranglers with this engine was as follows:


MPG in City

MPG in Highway

Combined Average 

4-speed automatic 




6-speed manual 




Maintenance and issues in 3.8L-V6 Engine On Jeep Wrangler

This engine has an excessive oil consumption, roughly around two quarts every 100 miles, and needs to be serviced regularly due to various factors like rust in various parts in the engine as this can damage the power output or cause other general problems and fixing problems in this type of engine does not come cheaply. The solution to the rusting is to apply an anti-rust solution to the main parts of the engine. 


  • The only advantage with this engine is that it produces slightly more power but this power comes at a cost. 


  • Expensive to maintain. 
  • Lower mpg.
  • Not long-lasting.

Based on the above reviews, we are going to do a comparison of the two engines according to the specific vehicles they are fit in and make a verdict on the better engine choice and wrangler model for a wrangler enthusiast.  

Recommended Maintenance Accessories For 3.8L-V6 Liter Engine

Performance Comparison of 4.0L-Inline & 3.8L-V6 Engine on jeep wrangler

4.0 Inline or 3.8 V6 engine for the jeep wrangler

Performance-wise the 3.8-liter v6 makes more power than the 4.0-liter inline-six but does this at higher RPM. This shows that for the 3.8-liter V6 to make maximum power you have to wait longer than the 4.0-liter inline-six.

Also, the 4.0-liter inline-six makes more power at lower RPM than the 3.8-liter V6.  

The ability of the 4.0-liter inline-six to make some reasonable amount of power at lower RPM than the 3.8 liter shows that it uses lesser fuel to do so thus the mpg of the 4.0 is lower.

The fuel cost of a 4.0-liter inline-six is much lower than the fuel cost of the 3.8-liter V6. 

It has also been noted that the 4.0-liter inline-six performs better off-road because of its ability to produce more power at lower RPM compared to the 3.8-liter V6.

However, if you want to make your off-road experience more fun, you can invest in some more advanced vehicle parts like lift kits and bigger tires. In this case, the 4.0-liter engine takes it to another level.

Maintenance Comparison Of 4.0L-Inline & 3.8L-V6 Engine On Jeep Wrangler

The durability of the 4.0-liter inline-six is unmatched when compared to the 3.8-liter V6 as it has lower maintenance issues and was manufactured with stronger materials.

The 3.8 have some issues and are listed as follows:

  • Rust in different parts of the engine.
  • Oil consumption.
  • Failure after 100,000 miles. 
  • Engine knock on startup. 
  • Getting used to the starter. 

The 4.0-liter also had some issues and are listed as follows:

  • Engine noises. 
  • Low oil pressure. 
  • Cracking or leaking exhaust manifolds. 

However, all the issues that the 4.0 liter had begun after the odometer had clocked over 150,000 miles and were very easy to repair compared to issues in the 3.8 liter.

From all the info gathered about the two engines, The 4.0 liter is way better and more efficient than the 3.8-liter but you can’t just choose the engine that you’d want on your wrangler since Jeeps no longer come with these engines.

Now, We’ll look at the vehicle specs that had these engines in them i.e., the jeep wrangler TJ and the jeep wrangler Jk respectively came with the 4.0-liter and 3.8 -liter engines and compare the whole car, in general, to see which one is better off. 

On the streets on paved roads the JK is quicker than the TJ since it has a slightly more responsive throttle response than the TJ, however, the 3.8-liter JK blows because of constant revving and it doesn’t like that.

Revving the 3.8-liter Jk will put your engine at the risk of blowing. In low range gear it performs perfectly but in high range is where issues are at. 

Mpg of the TJ is also lower so you get a better fuel economy than that of the Jk. The same case applies to the maintenance costs. That of the TJ is much lower since it has lesser issues as compared to the Jk.

The TJ is a little bit technologically outdated but if you are looking for a reliable and capable rig then the Jeep Wrangler TJ is the vehicle for you. 

Some owners though might want to have the 4.0-liter engine but not in the Jeep Wrangler JL since it’s the most loved engine. Some Jeep Wrangler enthusiasts perform engine swaps on their vehicles.

4.0 Inline or 3.8 V6 engine for the jeep wrangler

This has to be done with some considerations such as engine mounts and electronics. It’s usually costly to undertake an engine swap but if you intend to keep all the electronics the swap won’t dent your pockets that much.

Though putting a 4.0-liter inline-six in a JK or any other jeep after its time won’t help that much in increasing the power of the car. The only thing that you’ll achieve by performing the swap is a long-lasting hardcore engine that won’t have any issues and will be easier to maintain.

But, if you want power swapping your stock engine for a V8 is much better but we all the V8’s fuel economy. The 3.6-liter V6 is also not a bad option since it’s more powerful and capable than the 3.8-liter V6 and the 4.0-liter inline-six. 

how you can Maintain your Engine performance regularly 

5 Things you can do to maintain your engine performance, suited for both 4.0 & 3.8 Liter engines.

  • Make sure you change the oil filter of your jeep every 3500 – 4500 miles.
  • Rotate the tires to maintain balance for every 6000 – 8000 miles so that the tire pressure doesn’t affect your engine performance.
  • The air filter should be checked and replaced every 20,000 miles.
  • Flush and refill your cooling system every 50,000 miles.
  • Wheel alignment should be checked every 20,000 miles. It may depend on what kind of terrain you are on. Better to inspect closely and change tires if the old ones are worn out.


The 4.0-liter is much better in all categories except maximum power but when you look at it from a different angle, the 4.0 liter takes lesser time (according to RPM) to reach its maximum power output as compared to the 3.8-liter. 

When it comes to maintenance the 4.0 takes the trophy, because it doesn’t have as many issues as the 3.8-liter V6. The Durability of the 4.0-liter is much longer than the 3.8-liter.

A 3.8-liter starts developing issues after a few thousand miles on it especially if you use it regularly for off-roading, while the 4.0-liter can easily clock 100,000 miles without any issues and some drivers have even shared that they have clocked more than 200,00 miles on a TJ wrangler with the 4.0-liter engine without having to repair major engine components. 

Overall in every angle, the 4.0-liter inline-six is way better than the 3.8-liter V6 and it’s the engine you should choose if these were the only engines being offered, also seek professional consultation when you decide to undertake an engine swap. Hope you got an idea about selecting the right engine.