"Can't start in the back. That's how you get an infection." I laughed WAY too hard on that one!

Fun fact. This engine was designed by engineers from all the big three makes. AMC came around and they stuck this in about everything. When AMC disbanded Chrysler kept using the engine. It has one of the longest production life spans of any engine.

Just did a 2004 XJ with a 4.0. It had two pistons that dropped their skirts. 279,000 miles. The customer replaced it with a reman. This is a common issue with the High Mileage 4.0s. What happens is as follows. It starts to overheat or run just a bit on the higher side of 220 degrees. The piston skirts crack or break off leading to it burning some oil. The oil soot covers the 02 sensor, and tricks it into thinks it is running rich. So the computer adds timing and lean out the fuel to get it within spec. Only to melt down the already damaged piston, and this is the end result.

Finally a 4.0 teardown! And my god I've never seen that damage to a 4.0 in my life. I daily a 1995 Jeep Cherokee with 254K on it and it runs pretty nicely.

Good to see an uncomplicated old style basic engine that anyone could work on without a shop full of electronic gadgetry and specialist tools..

Got a 2001 Cherokee with 263,000 miles original motor daily driver rig. Impressive to see what abuse these motors can take til they let go.

Can you imagine going in for a physical exam and your doctor making the same noises as Eric does when he examines this engine block?!?! (Hmmm....maybe it wouldn't be that funny after all. 😱)

I have a 2001 XJ and it has been rattling for eight years, so bad I tell people that it's a Cummins swap. I paid a mechanic to drop the oil pan and take a peek. He couldn't find any loose so he buttoned it up and said to just ignore the rattle and keep driving it. That was eight years ago.

I like the 4.0 because of it's AMC lineage. But those cracks in the head you saw are common on certain years, and that's Chrysler's fault, because they redesigned the head. After a couple of years, they saw the common failure pattern, and came out with yet another redesign that fixed the cracking problem.

I've seen that kind of damage in 4.0L in-line 6 before. The 2 main reasons are 1) Prolonged high revving from trying to get unstuck in deep mud, or 2) very steep angles during rock crawling. I have owned many Jeep (Chrysler models) over the last 35+ years. Being involved with off-roading clubs has given me experience with the typical failures for people pushing their vehicles to the failure point.

I owned a 97 Cherokee with the 4.0L. After 212k miles the engine still ran strong. Like you said, everything around the body was falling apart or broken, but the engine always started up.

My brother had one of these in a jeep that had over 200k. It had a cracked radiator so he'd have to refill it. Sometimes he would drive longer than 30 minutes without coolant and the temp pegged on H and when he got home it would be bone dry. Drove like this for a few months. He had it for a year more and sold it to the neighbor who had it for years. Have to work hard to kill a 4.0

The 4.0 "AMC" and Furrrrd's 4.9 300 straight 6 are both legendary in similar ways. I had a '81 Bronco with the 300 and a manual 3-speed ( with overdrive) that was one of my favorite trucks ever! 300,000 miles on that truck. Too many things went wrong too quickly on the Bronco so I sold it as a parts truck. The 4x4 still got me anywhere I needed to the very end. 🏁

After just tearing a toilet apart going spelunking for my headphones, I needed to see someone else tear something else down and get gross.

I bought a 1996 Grand Cherokee with 267,000 miles on it. It was my first Jeep. It had a slight tapping coming from Cylinder #6. Started using T4 10/40 in it and it quieted it substantially. Drove it till about 301,000 miles and then it developed a really loud chatter. Still drove it another 2,000 miles that way till I finally bought another vehicle. I got curious and dropped the oil pan. The piston skirt for cylinder #6 was laying in the pan. Engine still ran and had good compression. Just piston #6 was chattering around in the cylinder.

So glad to see the 4.0 inline 6. They are so hard to find as cores. One of the best engines ever made. Would still love to see a GM 3800 series engine on the channel, or a 3.5L V6 from the 93-97 Intrepids/Concords

The other reason they were so popular was the ability to stroke them with a good set of 4.2 piston, rods and crank. That’s a good way to get power.

For a piston skirt failure, that one actually seems pretty tame. Usually the piston comes apart and the wrist pin hammers into the block until it either makes an inspection port or it seizes.

The cylinder head definitely feels like 89 lbs when you are leaning over the front of the jeep or the fender to remove it and even more when you are putting it back on

I've got a 1946 cj2a and it's still running the original 4cylinder GoDevil engine. Built to last!

Had a 99tj with about 90k on it break a skirt on the piston on cyl 6. Thought it was a rod knock at first. Pulled it and tore it down. Found the rod on cyl 4 visually bent as well. Never hydrolocked it. Figured I had it apart so go big or go home. Went .030" over, stroked it with a 4.2L crank, Comp Cams camshaft, bigger injectors amongst exhaust and others. I was very happy with the build!

There is a clear crack in the cylinder head, between #2 and #3 rocker arms. It can be seen just by removing the oil fill cap and looking in the valve cover. I was a jeep tech in the early 00s, this was very common on 98-03 cylinder heads. I replaced hundreds under warranty.

13 years as a flat-rate mechanic, owned 7 XJs (have one with nearly 300k miles), and I have NEVER seen this level of damage to a 4.0l.

A mechanic friend told me a story about one of his customers that had towed a Cherokee using a front axle type dolly for about 50 miles and then remembered that he had forgot to take the trans out of low gear and then found the engine wouldn't start. He pulled the head and ALL pistons were missing- just con rods and wrist pins were left...

Your videos keep getting better and better! I love watching you channel, its relaxing and entertaining. Always looking forward to seeing your new tear-downs and project updates. Your commentary is my favorite part lol. Merry Christmas man!

Thank you! Another one off the list! This engine is, of course, one of the most durable and torquiest motors available from the late seventies through the early aughts. The inherent primary and secondary balance of the straight six aside, just the combination of torque, ease of maintenance, and simplicity all made it the absolute pinnacle of the Wrangler powerhouse. This engine is still the best 6 cylinder that has ever been in a Chrysler product (slant six aside), and I have a couple customers that have their Grand Cherokees and wranglers up past 300K. Having to drop the 242 and the 318 from their lineup has left FCA continuing to fight for a 6 or 8 cylinder gas engine of any sort of quality, a fight that to this day has not been won. Yes, I know what I said. The Gen 3 hemi is barely worth its weight as a boat anchor. Of course you're not going to have a problem with the dipstick tube - it's not on a GM product. Engine Requests: Ford: 300 Inline Six, Windsor, FE, 1.0 EcoBoost, 1.4 EcoBoost, 5.2 Voodoo, 6.7 PowerStroke General Motors: 3100/3400/3800 Olds, LUW/LWE 1.8l i4, L5P Duramax Chrysler: Slant Six, MORE HEMIS, 1.4L FIRE, 3.3/3.8, 318/360 Honda: B Series, D Series, K Series Toyota: 1GZ-FE, 1ZZ or 2ZZ Subaru: FJ series, EZ30/36 Other: DT466 Old School Unicorns: GM 702 Twin-Six, Oldsmobile 5.7 Diesel, LT5 Lotus (C4 ZR1) Modern Unicorns: Toyota 1LR-GUE, Chevrolet Gemini, 7.3 Godzilla

Had the same 4L in a jeep Wrangler in the shop this past year, thing had completely seized, and when we pulled the pan there was mud in it. When asked, the owner denied having driven it in water or anything. We sent it away for a complete revision along with boring it out into a 4.6L. It now makes 300 hp and 600 Nm of torque.😁 Was quite a fun project. Had to modify and rebuild the entire jeep as it wasnt roadworthy anymore. One hell of a project for me and another mechanic, but a lot of fun

You did an excellent job showing the damage; very well done video!

Had a 95 GC with the 4.0 with 325k when I sold it. Only problem I ever had with was the water pumps shreading every 20-30k miles. I got very good at that routine maintenace.

Yes, Finally!!! My favorite engine too. In fact, I'm dailying my 04 WJ at the moment because well, it's the only thing I own that doesn't ever break. From what I remember, somewhere around 2000-2002 were the problem years with cylinder heads cracking, at least for the WJ. By around 03 and definitely for all 04's have a different head (denoted by the "TUPY" stamping under the oil fill cap) that isn't prone to cracking. I'm 32 and I expect my 4.0 to outlive me!

Hey Eric, I really enjoy your channel. I love taking things apart and really bad at putting them back together. Thank you.

Since that engine development was started in 1956 by Nash, then it was made by Hudson, then made by Rambler, then made AMC, then made by Chrysler for Jeep… After 50+ years, they better have figured out how to make it work right!

Don't trash that block! It may be suitable for an overbore as long as there are no cracks in it. Someone might be interested in buying it for a stoker build.

That was some impressive damage! Great video as usual. There’s a couple 4.0’s in my driveway.

As always, educational and fun! Thank you!!!

UK mechanic here, I absolutely love the channel, I'm addicted. You do a lot of complicated big blocks I would love if you could do some small European engines like some small inline 4 cylinders as that's mainly what we drive over here and their an absolute breeze to teardown and rebuild 😊

There was a little known issue with water pumps. The inline sixes had 2 water pumps. V grove turned one way. Serpentine turned opposite. They could easily be switched and the coolant would not circulate properly causing meltdown of the center two pistons.

My son bought a 2004 Grand Cherokee with the 4.0 and drove the hang out of it. I got it and drove the hang out of it then gave it back to my son, and he drove the hang out of it then gave it to his father-in-law, and now he's driving the hang out of it. The computer is starting to go away, but the engine's been solid.

thanks you for doing this awesome tear down. im a xj guy and love these engines.

How good you show everything and speed up the simple things, learn very much, thank you so much!!

Love my 95' 4.0! It's just broken in at 205k miles. I replaced the water pump and thermostat on my own. Pretty easy to work on

Sold mine after 350,000 miles and it still ran great. It was the family adventure vehicle. Heavy loads and back country roads were no problem for our 1995 sport. It did have a cracked exhaust and after my son used it two of the engine mount studs were cracked. I welded the engine mount back to the studs and it was good to go.

Hey, you answered my question about where the milage was stored on the Corvette. You are amazing!! I love to learn and you are great at educating.

Nice one Eric, your tear down videos are always worth following. HAPPY XMAS to you and your tribe. 🎉🎊🎉✌

I really appreciate how you speed through repeated bolt removal once the initial fastener is dealt with like on heads and rockers. Very enjoyable and informative stuff!

Merry Christmas and a Happy New Year! Thanks for all the humor and jokes throughout all these tear downs and projects! You are like an auto coroner on the channel, but you also save a lot of cars from the salvage yards. You should be called the car doctor for all the autopsies and projects. Keep up the great work!

Your fast forward sounds are very satisfying. Specially when your tq somthing down and you Hear the clicks. 😮

Somebody sponsor this mans supply of brake clean! Love the teardowns keep it up.

Eric, Merry Christmas to you and your family. Thanks for taking us along with you this past year. I’ve enjoyed your videos, your humor and presentation style!

That version of the 4.0L was used in the 2000-2006 jeep wrangler, and the 1999-2004 grand cherokee, I can tell by looking at the water pump and the accessory drive

Got a 97 with an old trw 5.0l stroker kit and a hesco aluminum head. Threw on an m90 blower and a pacesetter header blowing through a dual 2 3/4 exhaust. Sounds awesome and just will not die!

Love the videos, been watching for about a year now and I always look forward to when you upload. I’m not one to make requests usually but if you happen upon a Rover V8 4.0 or 4.6 from the P38s and Discovery’s, I’d love to see it. Keep up the good work.

love the Jeep 4.0 and the Ford 300 6 cylinder engines

Please find a blown up 3800 series pre 2004. I want to see how someone can kill a very reliable engine

Another excellent video, good job! Have you considered doing a series on putting some back together?

👍 thanks for making me feel better about my 4.0 with 319k miles on it! It's had a oil leak on the last 2 cylinders coming out the head gasket for about 60k miles. It's always been on my "I'll get around to it..." list.

I look forward to Saturday evening so I can see what you're going to tear down! Thank you from an armchair mechanic!

I've repaired quite a few of those with piston skirt failure. Overheating doesn't help things either. They start making a thunking noise like tapping on a tin can at idle when they start failing. Those can be repaired with a set of pistons and rings. I always opted to do the timing chain and bearings. They literally run for ever if you catch it early. The last one I did was a 2001. Thanks!

Wow. Amazing detail. Great job. I am now subscribed.

Good save with that drain pan!

That block would be good for a over bore and then a stroker setup.

Man as much as I watch these.. I always laugh when you throw away the "good" water pumps.

had one and loved it. great vid

Thank you for finally doing one

I was waiting for a jump scare looking in those manifold openings

Since the cylinder head cracks line up with the most damaged pistons, I'll guess coolant was getting into those cylinders causing detonation, which leads to the torched pistons. I'm impressed the pistons didn't come apart with how loose they were on the wrist pins!

When you rotated the engine and all of the tappets fell out it brought back fond memories of my 83 CJ7 and it’s lifter problems. Still runs great today.

"Can't start in the back, that's how you get an infection" LOL man, I laughed sooooo hard

Yes finally. I’ve been wanting to see one of these bad boys for a while

I'm convinced that inline engines are better than V4 or V6s. Just my opinion.

Love your tear downs ! Great shows

Great catch on the pan!

The exhaust manifold isn't difficult unless you own a Cherokee lmao 🤣 that was probably the most time consuming repair i've had to do to mine lol

You magnificent madman, you finally got one for us! I've owned many Jeeps with the 4.0, XJs and ZJs both, so this is going to be fun. Besides piston skirts and the TUPY heads, these were solid. Although the cooling system was rather inadequate in the XJ, application. You have to ON TOP of cooling system maintenance on those. ZJs were a clean sheet design, so the 4.0 was integrated correctly in those from the get go.

Great catch with the oil catch pan. Love your videos, and commentary LOL

The later 4.0L engine built between 1999 and about 2002 used a head casting #0331 and was prone to cracking between the 3rd and 4th cylinder due to the exhaust port redesign to meet emissions. This same head casting #0331 was redesigned and they added a TUPY casting mark on the surface of the head just under the oil fill cap. The head with the TUPY marking was corrected to prevent this cracking. The #7120 casting between about 1996 and 1999 I believe is the best for performance as it was less restricted before the emissions redesign.

Classic case of an over heating engine and the driver just saying "F' it, going for broke and going run this heap till it seizes!" I bet that baby sounded quite delightful running down the road with pistons screaming going into Chernobyl meltdown mode and I bet good money it smelled truly delicious, truly a worthy honorable mention meltdown. Thanks for sharing, glad I found your channel.

Those Valvoline oil filters don't have a bypass valve, seen them plug up and cause codes or destroy engines several times

Great tear down, Merry Christmas!

I 100% agree with the early exhaust manifolds. I would be replacing at least one a week at the Midas shop I worked at. The replacement ones had a small flex section on the number 1 and 6 pipe to prevent a recurrence.

Hey Eric, love the video, would you ever do a Big Block Molar teardown? Would love to see a 440 or an old AMC 360.

My brother had a box style Cherokee, with the high output, I think they called it, it had over 300,000 and ran like new! You couldn't kill it, he traded it in on a new car.

Thank you for doing the 4.0L ... I have an 80 CJ with the 258. Never seen a melted piston like that in a Jeep I6!

As always, excellent video with witty commentary. Thanks.

Greatest engine AMC produced (RIP) and one of the greatest engines of all time.

That dipstick removal really makes this engine a contender for the GOAT

Finally! I'm glad you finally made a video on this engine. The 4.0L is the only good thing about my jeep and it still isn't perfect. I just read the description and my uncle has a 2004 WJ grand cherokee with over 350k miles it takes literally a minute of cranking but it still starts and runs

My favorite part of your videos is where you analyze a part… say “It’s pretty good. We can use it as a spare or back up.” Then , toss it into the junk pile. I don’t know if I’m the none who gets your sense of humor, but I love it!!😂😂 Love your videos!

Wouldn't mind seeing what the burned Vette engine looked like up close. Even if you don't wind up tearing it down.

First 2 causes that jump to the top of the list: 1. Hydrolocking 2. Overheating

Im new to your chanel, enjoying everyone of your videos. I loved rebuilding engines in my younger days and may rebuild my 4.7 in my 2000 jeep wj.

Love your commentary as you tear down the motors , entertaining vocabulary 😅. Keep it going

Man that 4.0 was ridden hard and put away wet by the previous owner.

Ah yes, the simplicity of rocket surgery 🤣

Very good video! Thank you once again for GREAT content!!

One time I pulled apart a 4.0 from like a '92 Comanche and it had been run at least 60 miles distance with pieces of a broken valve riding bouncing around inside a cylinder. Top of the piston all scarred up and walls not perfect. I ground the top of the piston with a dremel tool, threw on the rebuilt cyl head, and it ran perfect for over 10K miles until I sold her.

Which is more ... bulletproof, in your opinion. 4.0 L Jeep or 225 CI Slant Six ? Have you torn one of these down. I had one (moons ago) which continuously had 'grey' oil and a leakiny rear main (fill the oil, check the gas). TBH, the oil leak kept the body of the D-150 (A833) frame from rusting. The carbon (1bbl) kept the exhaust from rusting.

A 4.0? Tough motors!

Thanks for another great video. 👍

I had a guy drive his wifes 99 jeep Cherokee 25 miles into the shop the 4.0 ran decent but had a miss never made any noise but when we pulled the head off #6 piston was gone!! didn't scar up the cylinder at all we dingle berried the thing put a new piston and wrist pin on the rod reused the rod bearing because it still looked great and she's still driving it today 3 years later. The head casting on these are junk. But with much needed radiator upgrades these will last for a long time. AND A 180 DEGREE THERMOSTAT IS A MUST!!!