AMC/Chrysler/Jeep 4.0 Engine

The Jeep 4.0 isn’t just a legend in the Jeep world, but likewise the automotive industry as a whole. AMC occurred this engine before Chrysler buying them out in 1987. It’s a solid and reputable engine, however, the 4.0L straight-6 is likewise known because that a absence of power. Regardless, the 4.0 is wonderful all approximately engine that many appreciate to this day. Good enough the Chrysler and also Jeep preserved it roughly for almost 20 years. In this article, we talk about Jeep 4.0 engine problems, reliability, specs, and more.

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*Some additionally refer come the 4.0 inline-6 engine together the PowerTech or 4.0 PowerTech. We might refer to the Jeep 4.0L engine by these names in the article. We might additionally call that an AMC, Jeep, or Chrysler engine.

What Cars usage the Jeep 4.0?

AMC/Chrysler/Jeep 4.0L straight-6 engines space in the following years and models:

1987-2001 Jeep Cherokee1993-2004 Jeep grand Cherokee1987-1990 Jeep Wagoneer1987-1992 Jeep Comanche1991-2006 Jeep Wrangler

4.0 Straight-Six Engine Specs

Initial development of the 4.0L inline-6 engine was in 1986 – simply one year prior to Chrysler bought out AMC. Despite this fact, Chrysler opted to keep the AMC draft 4.0 around for the lengthy haul. Though, Chrysler did do a number of updates come the straight-6 over the years. We’ll circle earlier to this suggest and sheathe some in-depth specs in a moment. The listed below chart shows a few of the basic specs because that the Jeep 4.0 engine:

EngineAMC/Jeep/Chrysler 4.0
ConfigurationStraight-6 (Inline-6)
Displacement3,965 cc (4.0L)
AspirationNatural
Block MaterialCast iron
Head MaterialCast iron
ValvetrainOHV
Bore x Stroke98.4mm x 86.7mm
Compression8.8 : 1 come 9.2 : 1
Power173-190 HP
Torque220-235 lb/ft

As the engine name suggests it’s a 4.0L inline-6 engine. Yes, really displacement is roughly 3,965cc i beg your pardon is rounded as much as 4.0L. Actors iron heads and blocks were normal ago in the 1980’s and provide plenty the strength. They’re regularly not uncovered in contemporary times due to weight. Jeep 4.0 engines space overhead valves unequal the standard overhead or dual overhead cams of the modern days.

Power started at 173hp in the initial 1987 models. Output was easily increased come 177hp in 1988 and then 190hp in 1991. Torque additionally improved end the years. Of course, throughout its virtually 20 year manufacturing the 4.0 straight-6 observed a number of updates. Some assisted increase power and torque when others were intended to enhance efficiency, strength, and also reliability. We’ll cover a couple of of this updates quickly in the following section.

Jeep 4.0L Inline-6 Updates

It’s essential to keep in mind – this is not an exhaustive perform of all updates. Two decades is a lengthy time for an engine to it is in around, and many tweaks occur during that sort of timeframe. Anyways, a few notable updates because that the Jeep 4.0 straight-6 engine include:

1988 – higher flowing fuel injectors1991 – Multi-port fuel injection replace instead replace RENIX, intake port raise 3.2mm, larger throttle body, entry & exhaust manifold updates, higher flowing injectors, electronic came timing updates1995 – alters to cylinder head1996 – stronger engine block2000 – Cylinder head architecture changes for greater efficiency & distributor-less coil ~ above plug ignition system

Again, over there are various other minor tweaks and changes over the years. One year after arrival the Jeep 4.0 engine receives greater flowing injectors i beg your pardon help add a few horsepower and torque. 1991 witnessed a grasp of update that enabled the engine to make 190hp. A couple of small updates come the head and also block developed in the adhering to years. Eventually, in 2000, Jeep 4.0L engines observed a couple of design transforms to help support lower emissions and also greater as whole efficiency.

Jeep 4.0 Straight-6 Engine Problems

Alright now we’re moving onto a couple of of our larger focal points because that this article. As legendary as the 4.0 inline-6 may be it’s still prone to running right into engine problems. This is true for any automotive engine, and also especially so when talking about a 15-30+ year old engine. A few of the most common engine troubles on the Jeep 4.0 encompass (in no specific order):

Exhaust manifold cracksOil leaksWater pump & thermostat

We’ll rest the above issues down in greater depth throughout this article. At the end we’ll finish up v thoughts on overall reliability. That will also lead us right into our last discussion around rebuild kits. Numerous owners still adore the Jeep 4.0 straight-6 however age is a big factor here. Over there are most likely tons of Jeeps the end there with the 4.0L straight-6 that are running the end of time due to old age and also high mileage. Together such, Jeep 4.0 rebuilds and also rebuild kits room a common theme.

1) Jeep 4.0L Exhaust Manifold Cracks

Exhaust manifold cracked is without question one of the most usual problems on the Jeep 4.0 engine. This is particularly true through the age and also mileage of many 4.0L straight-6 engines approximately today. Fortunately, it’s a quite minor worry in the grand scheme. Exhaust manifolds may likewise be recognized as headers or exhaust headers.

Sometimes that may simply be the manifold gasket or bolts bring about the issues. However, it’s likewise common because that the manifold come actually build cracks. Symptom are many noticeable on a cold engine. As the Jeep 4.0 inline-6 exhaust manifold heats up and expands. This development can help close the crack, for this reason symptoms might go away as soon as the engine warms up.

AMC 4.0 Exhaust Manifold crack Symptoms

A couple of symptoms that a cracked exhaust manifold ~ above the Jeep 4.0L PowerTech engine include:

Ticking soundsRaw exhaust smellVisible cracking

Exhaust manifold crack typically reason odd engine sound – significantly a ticking noise. Again, this may only be present on a cooler engine together the cracks end up being smaller with heat. You could also notification the Jeep 4.0 smells person that is abnormal stronger prefer raw exhaust. Though, this can be difficult to notice with tiny cracks. Otherwise, a visual inspection could confirm if and where cracks exist.

4.0L Inline-6 Exhaust Manifold Repair

There are number of viable options if you run right into a cracked exhaust manifold on the Jeep 4.0 engine. You can opt because that an OEM solution, however sometimes new parts can be challenging to monitor down. Offered Jeep exhaust manifolds may quickly run right into the same worries so be cautious.

Aftermarket Jeep 4.0L straight-6 exhaust headers room a good choice. However, modding the exhaust might be viewed as illegal and also can reason emissions concerns. Nonetheless, it’s a great option to hopefully stop running into an ext manifold leaks in the feature.

Finally, friend may be able to repair your cracked Jeep 4.0 manifold. Some have success v this option, yet others uncover it to be a short-term solution. This have the right to be a good, cheap choice for AMC straight-6 owners who don’t mind a DIY project.

2) Jeep 4.0 Oil Leak Problems

Well, this one access time close to home as huge BMW enthusiasts. Plenty of of the very same jokes around oil leaks float around in the Jeep community, too. In reality, oil leaks impact many engines therefore the Jeep 4.0 engine is no alone here. Part Jeep oil leaks space simply as result of age and mileage while rather were well-known to be faulty from the at an early stage days.

The Jeep 4.0 valve cover, valve covering gasket, and rear main seal room a couple of of the most usual oil leak problems. End time, this seals and gaskets stay down and also begin cracking. Oil leaks typically start as a tiny leak and also gradually become worse as cracks expand and brand-new ones develop.

With the period of the AMC 4.0 straight-6 it’s likely many engines space leaking or had actually previous oil leaks the were repaired. If you’re in the industry for the 4.0L engine definitely look for any kind of leaks and also see if any of these repairs were excellent in the past.

Chrysler 4.0L Engine Oil Leak Symptoms

Symptoms that oil leaks might be noticeable to some. Nonetheless, look because that the adhering to symptoms the may point to an oil leak ~ above the Jeep 4.0 engine:

Visible leakBurning oil smellsLight smoke indigenous engine bay

Visible autumn of oil ~ above the floor is a dead give-away oil is leaking indigenous somewhere. Once the 4.0L inline-6 is leaking from the rear key seal it frequently drips onto the ground. However, valve cover gaskets lie in ~ the top of the engine so little leaks might not make it come the ground.

With Jeep valve cover gaskets check for potential burn oil smells or light smoke from the engine bay. You could also notification some oil pooling around the valve sheathe gasket area.

Jeep 4.0 Oil Leak Repairs

The DIY crowd will certainly appreciate the truth that this Jeep 4.0L oil leaks room cheap repairs. Gaskets and seals often come in for much less than $20, therefore a pair hours in the garage have the right to save a lot of money. Those walking to repair shops will uncover bills to be a little bit pricey as result of labor costs.

Rear main seal replacement deserve to run $300-500+ in ~ a repair shop. It’s a fairly labor extensive job. Valve covering gaskets are quicker thanks to the simple engine style of an inline-6.

3) 4.0 Straight-6 Water Pump Failures

Overheating is an additional common worry on the Jeep 4.0 straight-6 engine. The water pump and thermostat aren’t always to blame. However, they’re typically an excellent starting points and a common cause of overheating. This wasn’t a significant issue once these engines to be newer. However, water pumps take a many abuse end the years and are usual repairs on numerous aging engines.

Water pump worries are a pretty immediate repair on any type of engine including the 4.0L Chrysler PowerTech engine. The engine is known to construct head gasket troubles on occasion, too. Those failures end up being a lot an ext common as soon as the 4.0 liter engine is subject to overheating.

Another concern outside of actual water pump failure is the pump flow. Some OEM pumps don’t flow very well at reduced RPM’s and also idle, which can likewise cause overheating. Fortunately, there are some aftermarket services that help solve this trouble on the Jeep straight-6 engine.

Jeep 4.0 Water Pump fail Symptoms

Symptoms the water pump troubles on the Chrysler/Jeep 4.0 engine include:

Coolant leaksSteam indigenous engineOverheating

If you notice a coolant leak then the water pump may be come blame. In some cases the coolant loss can be very rapid and you’ll even an alert steam from the engine together it leaks out and burns off. This deserve to lead to quick overheating on the 4.0 cool Cherokee and Wrangler.

It’s essential to for sure the engine does not overheat, so if you notice this symptom shut off the engine as quickly as possible. To run the engine too warm for long periods rises the hazard of extr problems.

Jeep 4.0 Engine Reliability

Is the Jeep 4.0 straight-6 engine reliable? Yes, we believe this engine earns an excellent remarks for reliability. AMC was struggling financially when they developed the 4.0L engine. Together such, AMC opted to use some older yet proven and an easy engineering for the straight-6 engine. Many take into consideration the 4.0 amongst the best Jeep engines because that its simplicity, reliability, and also 4×4 capability.

However, no engine is perfect and also that uses to the legend AMC/Chrysler/Jeep 4.0L engine. These engines are well-known to run into problems such together exhaust manifold cracks, oil leaks, and water pump failures. This additionally isn’t one exhaustive list. It’s not completely uncommon to view head gasket, piston skirt, and also leaking fuel injectors among some other Jeep 4.0 engine problems.

Then there’s age which is a large factor once it involves the 4.0L inline-6. The engine regularly doesn’t have actually much problem making it past 200,000 miles and even 300-400k+ mile in some cases. That’s pretty good longevity and also reliability because that the Jeep 4.0 engine. Still, with the current age of this engines it’s likely they’ll require some extra TLC and also potentially a rebuild.

Jeep 4.0L Inline-6 Rebuild Kits

Given the allure the the Jeep 4.0 engine opting because that a rebuild kit is an increasingly typical choice. Most parts for the straight-6 room pretty inexpensive, so it’s no a bad deal for those who deserve to DIY. The course, rebuilds are an extremely labor intensive and also require a great bit the knowledge roughly an engine. Generally, rebuild kits incorporate something follow me the lines of the adhering to parts:

Seals & gasketsPistons & ringsRod bearingsMain bearingsCamshaft, lifters, & cam bearingsOil pumpTiming kit

This Jeep 4.0 rebuild kit is a pretty good example of what they frequently look like. During a rebuild friend can choose to carry out a bit less or take it things even further. Lot of of options exist for inner upgrades, stroker kits, forced induction, etc. Again, this stuff can include up to be expensive if you’re not qualified of act the job-related on her own. At the point, you might be better off sourcing an currently rebuilt engine and simply swapping.

4.0 Straight-6 Engine Summary

It’s no an enig the 4.0L straight-6 construct by AMC is somewhat a legend in the Jeep world. The 4.0 liter engine definitely doesn’t placed out much power by modern standards, but it offered solid power for that is era. Jeep 4.0 engines additionally use a an easy design that gives lasting longevity and reliability. There’s a factor Chrysler and Jeep kept an AMC developed engine roughly for 20 years.

However, no engine is perfect and also that uses to the AMC inline-6 engine too. A few common issues with the Jeep 4.0 encompass the exhaust manifold, oil leaks, and water pump. Other troubles like head gaskets, pistons skirts, and also crank place sensors additionally aren’t uncommon. A most reliability simply comes under to maintenance, for this reason ensure friend take an excellent care the the 4.0L engine.

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The Jeep 4.0 engine regularly holds up conveniently to 200k miles and also some even make it to 300-400k with couple of problems follow me the way. Not negative for longevity and also reliability. However, through the age of these engines it’s becoming more common that they require rebuilds. It have the right to be a costly endeavor, however some believe its precious the expense to own one of the greats.

What’s your experience with the Jeep 4.0L straight-6? are you considering one?