Jeep 4.0L: Everything You Need to Know 

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When the last JL jeep is taken to the scrapyard, it will be towed there by a 4.0L jeep.

'99 Cherokee with the 4.0 379,xxx miles and STILL runs like the day I bought it in 2000 with 11,000 miles on the clock. Most reliable vehicle I have ever owned. Might be why I've had it for 20 years. 😎👍

My 4 Liter knocks and will continue knocking for years. It doesnt give a shit because it's a 4 liter

Thanks for mentioning me (Frank Swygert). MY background on the AMC six is mostly on the car side, whereas you're obviously mostly on the Jeep side. Overall you did a great job! There are a few things I want to point out though. 1. The 232 six first appeared in 1964 in a special edition Rambler Classic two door hardtop coupe called the "Typhoon" -- after the engine name (that never really caught on, people just call it the Rambler or AMC... or Jeep... six). All were yellow with a black top and only 2520 were made. This was late in the model year (April release). The 232 was optional in other Classic models for 64 (for $59.95), but not too many were made. The 232 became available in the American for 1965, but not with air conditioning. The 232 is about 3.5" longer than the older 195.6. A special short shaft water pump (later used to put the 232 in CJ-5s) was used and the radiator moved about 2" forward. When the radiator was moved there was no longer room between the grille and radiator for an AC condensor. If you ordered the 232 and AC the AC option took precedence and you got the 195.6 anyway. A shorter stroke version of the 232, the 199, replaced the old 195.6 for 1966. The American was restyled with a slightly longer "nose" to create room for the standard length water pump and an AC condensor. 2. The 4.0L and 232 (and 199 and 258) are virtually the same block. The bell housing bolt pattern was changed in 1972 to be the same as the AMC V-8 (previously used the smaller 195.6 bell pattern), the deck height was increased in 1971 to create the 258 (which eliminated the 199), and the timing cover was changed in 1974 to accommodate different accessory mountings. To create the larger bore 4.0L (3.88" vs 3.75" for 199/232/258) the block was revised. It was made ~1/8" wider for the increased bore and the mechanical fuel pump mount was eliminated. Other changes were minor (like a couple extra casting holes... freeze plugs). Cams, cranks, heads, etc. will all interchange. The 4.0L uses a slightly wider and better design timing chain, which is sometimes used on the older engines. 3. Heads. There have been several 4.0L head versions which I won't get into. AMC/Jeep engineers really did all the work on the 4.0L, they just changed employers when Chrysler bought AMC. The work was done at the old Jeep facility by some of the engineers that were working there under AMC and developed the 4.0L. AMC changed the two center exhaust ports from a siamesed design (both center cylinders exiting into one wide port) to totally separate ports and raised the intake ports ~1/8" for a better intake charge entry angle in the RENIX head. The H.O. head intake ports were raised ~another 1/8" to further increase the intake charge radius. The early 2000 head, 0331 casting, did indeed crack more easily than others, at the location you indicated. You show a cracked head, but also inadvertently show a fixed head when showing the casting number. For some odd reason the casting number wasn't changed when the casting core was fixed. Instead the letters "TUPY" were cast across the head in the center. So if you have an 0331 casting you want to look for that TUPY -- which can usually be seen with a flashlight through the oil fill plug on the valve cover. 4. Another bit about the 4.0L head... It is a rather common upgrade for the 258, a bit less so on the 199/232. It's about 1.8" wider than the older heads, so the casting wash-out ports on the 4.0L head come very close to the edge of the 258 block (pre 87 258 -- I believe the 87-90 are the same width as the 4.0L). The head overhangs slightly on the right side (distributor side), but the ports don't. Being so close to the edge they may weep coolant once the engine gets up to temp and under pressure though. I've heard a couple people say coolant will "pour out". It might if core shift on a head casting was really bad, but I've done several head swaps and never saw one that bad. Those ports are just plugged (I've always used epoxy, some weld or drill round and use screw in plugs) to prevent this. Epoxy works well because the plugged area is fully supported by the block and head gasket. You must run a 4.0L exhaust manifold due to the center port change, and the valve cover design changed with the head, so you need a VC to match the head used. 5. Carbs on a 4.0L. For various reasons (cheap blow-thru turbo, racing class rules, etc.) some run carbs on 4.0L engines. Easy -- use a 258 intake by filing the bottoms of the "ears" with the hole to align the intake so that the ears sit on TOP of the alignment dowel and the top edge of the intake is even with the top edge of the head above the ports. Stick a 258 distributor in place of the 4.0L distributor (or later model cam position sensor). 6. RENIX vs. H.O. computers. You pretty much hit that one! I run a RENIX in my 63 Classic wagon. It's not that hard to diagnose, unless you're used to modern cars that at least give you a hint at what's wrong. It's more like a carbed engine, just slightly more complicated. Once you know what each of the 4-5 sensors do it's not too bad. There are a couple good diagnosis guides on-line. The H.O. computer was designed by Phillips. It's just an upgraded RENIX in most ways. The three big changes are that the EGR valve is eliminated (through minor cam and programming changes), the crankshaft position sensor was changed (Hall Effect switch in H.O., a magnetic coil in RENIX), and of course the ability to store codes. The RENIX does "store" codes, but the memory clears as soon as power is cut off. As you mentioned, there is no cheap way to read those codes either. At least the older Snap-On professional code reader would with the right module (expensive!) and the dealers had a reader (also expensive!). That's all that I know of, though some other pro readers of the era might. I probably missed something.. but those are the major points.

Probably the best american made engine in the past 30 years or more.

The AMC 242 is the only engine that hits the million mile marker so often its never even talked about. The legacy this engine left behind is just one part of how brilliant AMC was. In all my years I have never found a brand that is even half the brand AMC was. Just goes to show that whats popular isnt necessarily whats good. Otherwise AMC would be thriving to this day.

I knew most of the information in your video, but I enjoy hearing someone else who shares my enthusiasm and love for the 4.0 I6 talk about these engines. Thank you for sharing!!

I once bought a TJ rubicon from a used car dealer. He was selling for $4500. It had 309k miles on it and was previously owned by the border patrol. I gave him 3800 for it and I put another 120k on it in the years I had it. I bought a new wrangler and a guy across town bought that rubicon from me. I still see it around once in a while.

My first engine ever! Super easy to work on and Damn near bullet proof. If you’ve got one, hold onto it and treat it well. It will take care of you if you take care of it!

Had 5 Jeeps with the I6 4.0L engine. My last XJ had 200K and was running great. I just bought a 14 year old Jeep TJ with only 23K miles on it. Like getting a NEW Jeep. I tow this one behind our motorhome. Nope don't like the new minivan Jeeps. Will keep buying vintage until I cant drive anymore.

My 97' 4.0 turns over and starts before you even hear the engine fully cycle on the starter. Key touches the contact and BAM. It bangs, it smells like gas, she wakes up rough but after all these years, shes ready to do business 24/7. Love these engines.

My Jeep 4.0 has no issues. When I got it, it needed a radiator, thermostat, and water pump. Got those installed in an afternoon and almost 100k miles later, it's still going with no issues. It's not a fast engine, but it's quick for what it is. I've gotten it up to the top speed of 117 a few times and it didn't feel like it got heat soaked after that.

My YJ has the 4.0 straight six and it is so easy to maintain, work on, and after 3 years of sitting, a fresh battery charge, she turned right over. Tough engines man.

I tow a lot with my Cherokee. One of the aggravating problems with the 4.0 here on the Gulf Coast in Summertime is that the fuel rail sits directly above the exhaust manifold. On hot days pulling my 16' covered trailer, it will stumble on startup after refueling and other short stops. The fuel in the rail tends to vaporize. Not a serious problem but sometimes it will throw a "Cylinder misfire" code which I have to erase. I put a heavier duty electric fan on it earlier, but the final cure was a temp probe in the radiator fins that turns the fan on at 160 F and off at 120 F. Wired directly to the battery (with proper relays and fuses) it will run a few minutes after shutdown on the hot days and blow air directly along the fuel rail. No start up stumbling anymore. The only problem is trying to explain to people why "Your fan is still running". Only a few minutes and it shuts off, so no battery issues.

My mom owns a 2004 jeep grand cherokee with a 4.0l straight 6 and it has 200,000 miles on it and it runs like a champ !!!! 😁😁😁😁❤❤❤❤

The 4.0 is as reliable as a hammer, if it blows up you’re either doing it wrong, or you’re surprised it’s lasted as long as it did. Not to mention the smooth torque curve and nice low end.

I beat the absolute hell out of my 4.0L jeep for 280K before I sold it. Never plugged in once in Canadian minus 40 winters. Spent more time at redline then idle. Never burned a drop of oil. One of the best motors ever. Wish they would have made a slight redesign for little more power and mpg.

I will back you 100% on this one. Purchased a neglected MJ 4.0/AW4 with 190,000 miles on it. Drove down with a buddy almost 200 miles to pick it up. Not only was it way down on power when we got there but it only had 3rd and 4th gear unless you manually down shifted it to 1st and 2nd meaning it would start out in 3rd gear in drive. I was pretty disappointed but the guy came down to $850 and it had brand new tires. Drove it back all the way home painfully slow. Got it home and no compression at on on the front cylinder. Turns out bent exhaust valve. Resurfaced the head and found broken wires above the transmission. $500 later for having a machine shop clean up the head, new fluids, and of course a water pump and it ran great. I used it as a daily driver for a long time and sold it for $2500 years later…… looking back I still miss that truck.

250k miles on my 1998 Cherokee XJ with this engine. Just replaced the tires and took it on a long road and offroad trip through Colorado, Utah, and Arizona. Still chewing up roads like a boss. Zero engine trouble since I bought it in 2001.

You got it right bullet proof, I've been driving a 4.0 jeep cherokee for 8 months with a cracked head. No joke i put water in it every morning and I'm not scared to drive it hours away from home still!! MOPAR OR NO CAR!!!!

My 98 Jeep Cherokee is the most reliable vehicle I have ever owned, desert toy now.......I love her. Lol

I had my first 4.0 XJ on 300k miles, was very happy with it and it did not have any issues at all for 60k+ miles during I had it. Got my 2nd XJ on 120k miles few years later, I seriously did not feel any performance drop neither on the engine nor on the transmission. For 100k miles it only wanted oil and water like the old one, and that's it. Never skipped a beat, never left me on the road, never embarassed me.. There was not a single day I thought "will my Jeep run or make this 1000k journey". It always did and I always knew it could.

4.0L is the best engine feeling ever ... so reliable .. I have a BJ60 with a 3B and still ... love this 4.0liters

The 4.0 Jeep and the 4.9 Ford inline six can take a lot of punishment!

They should bring that engine back in my opinion. Best engine ever made.

This engine is incredibly bulletproof. My friend bought a non-running one that had been sitting for a few months, we put a new starter motor in and it roared to life.

One of my favourite engines of all time. Built like a tractor engine with 7 main bearings since 1964. Studebakers v8 is another of my favourites as well. I had a Comanche with the 4 litre and I should have kept it.

The one and only bomb proof engine.

That engine had the best sound. When my parents bought their first Grand Cherokee in 1993, they got the V8, but I preferred the in-line 6 when we test drove them due to its awesome sound.

My 4.0 was pretty rock solid. (97 XJ) Thumb up for the history.

I was an AMC Gremlin guy. That is what I always liked and the Hornet as well and I really liked the 258cid straight 6 and they were bulletproof. I am pissed that my 03 Grand Cherokee was 2000 miles away from hitting 500000 miles when a drunk driver reared me at 100mph. The 4.0 is the best straight 6 ever made. Great video and a props for the 4.0

my 98 4.0L is all original with 325,000 miles. Doesn't sound super healthy, but it doesn't leak oil yet, and still full on power.

One thing you missed mentioning: These engines are really easy to work on in XJ Cherokees.

I and my son have owned a number of Jeeps with this engine. It's a very torquey engine and with just a little work can be pretty powerful and last forever. I put a Borla header, Flowmaster muffler and high performance fuel injectors on my '93 ZJ 4.0 and was very impressed by the power.

I just got a jeep an yesterday with the 4.0 and I am so happy I love this motor

I have seen these engines take on water, we pulled the plugs turned it over and it came right back to life. No issues at all, I have seen these engines held on rev limiter for minutes at a time.

I'm in the UK, I've had several 4.0L's excellent engine apart from one massive issue. Fuel is over $7 a gallon here and a 4.0 has a serious drink problem

Few years ago I bought a 2004 Jeep 4.0L for my Utah off road run around. The longer I have owned it the more impressed I am with performance. After reading your article and watching your video I understand why. Very impressed with your provided info and just would like to say thanks and keep up the good work.

I have an '05 TJ Rocky Mtn with the amazing bulletproof 4.0 I6, which as you mentioned does not have the thin 0331 header, thank God. With just over 153k miles, it runs absolutely amazing. I've been using Valvoline 10w30 150K+ synthetic blend oil and have noticed a tremendous difference in how it idles and performs overall since switching over from the Valvoline 10w30 75k+ mile oil. I also use marvel mystery oil and BG44K products for gas and oil treatment. MMO is good but doesn't compare to BG44K in quality and effectiveness. I can see this 4.0 lasting no less than 500k miles before needing an engine rebuild. I ignorantly had an '08 JK X with that pos 3.8 mini van engine. And these engines are on the opposite sides of the spectrum, from worst to the best. I will never have another Jeep after '06. If I ever get another, it will be either a CJ-7 Laredo or a CJ-8 Scrambler with the 4.2L. But I will never get rid of my '05 TJ Rocky Mtn! Great video! O|||||||O 🇺🇸 Only in a 2 Dr 🇺🇸 '41 - '06

I hydrolocked my 4.0 and had it running In a matter of hours. It's still going strong to this day.

6:10 You showed a "tupy" head when mentioning the 0331 head prone to cracking. The "tupy" head is the improved head. 0331 without the "tupy" cast in between the cylinders should be avoided.

Thanks for reposting this video - searched for it a couple of days after I first viewed it several weeks ago and it was nowhere to be found...cheers!

I have a '91 Cherokee Larado 4.0-HO that just turned 250K with the only issue being the rear main seal leaking. I'm with you; I love that engine! Any issue I have had was not engine-related. Loved your video and agree wholeheartedly.

My father had on that he kept on the road to like 300k miles, kept tubing the floor out cause it kept rusting, the engine was still healthy and running when he finally had to let it go, cause of the rust issue, I just recently bought a 01 cherokee with the 4.0 with 180k, she is a beast and I plan on keeping her as long as I possibly can, she's may daily. Most reliable engine ever made !!

Had a 98 cherokee I ran hot every day for 3 months straight because of a bad radiator, ran it about 2-3 quarts low on oil several times because of a bad seal I eventually fixed along with the radiator. Damn thing still almost made it to 400k. They are definitely the toughest engine I've ever seen

Love the video. Thanks for doing it. I have a '98 TJ and a '98 XJ, both with the 4.0 I6. Each one is sitting just under 200k miles. I fix a lot of things on these vehicles and love how easy they are to work on and how easy it is to get parts. Both developed leaky pan gaskets. I've replaced the pan and RMS gaskets on the TJ. Gonna do the XJ this fall. I love these engines. Almost 25 years old, and they run really nice. Some day I might get one of those Golen mods, stroked out to 4.6L with 270 hp and 315 lb-ft torque.

Got a 95 grand cherokee with the I6 and the thing is a beast. One time I drove 250miles with only a single bolt holding the head gasket together (bad mechanic screwed me) and after getting a new head gasket seal the thing ran perfectly. Told the story to a customer one time and the guy wanted to buy it on the spot lol. I only got 116k miles on her but I plan on keeping her till I'm old(26 atm).

One of the beauties of the AMC 242ci I6 engines is that a child could successfully work on them with some training. It is so logically laid out and so simple to do what would be considered a major repair in other engines that this engine should have never been terminated. The only thing I would change is that the exhaust and intake manifold are on the same side. Other than that, I love the engine tremendously. I have had four vehicles with the engine and still have two of them. I will never part with my 1997 Jeep Wrangler I bought new nor my 1998 Jeep Cherokee I have had for nearly sixteen years. Modern vehicles are made so stupidly, flimsy, ugly, and over engineered that I will likely never get any of them. I work on thsf garbage for a living. I do not want to take my work home with me. Few mechanics drive modern vehicles. We know the dark secrets these piles of junk and plastic have. The engine auto stop and start design flaw is going to get quite a few people very soon. People have no clue what happens when an engine is turned off, allowed to go to zero oil pressure and then restarted over and over. But they save a spoonful of fuel. The thousands in engine they will spend is inconsequential. People are so clueless.

As an accomplished lifetime mechanic I've only seen one 4.0L jeep engine suffer a catastrophic failure. My buddies wife lost her tampon or something and took it out on his 95' cherokee and over-reved the piss out of it on purpose and it had spit the center of the cam out of the block.. He asked me to find out why it doesn't start anymore. So I popped the hood and seen a section of the camshaft sitting there next to the battery and said "well this might have something to do with your problem, besides from being married to a psychopath"..

My 99 Xj has almost 400,000 Mile's and is just like New.... Original Head Gasket and 🐈.. A real beast on the street and trail.

Best damn engine (in terms of reliability) ever made

Wow, absolutely great break down. As the owner of a 4.0l 94 XJ and currently a 00 XJ I found this video not only informative, but also dead spot on accurate. Especially the parts about the 0331 head cracking (been there), the rear main seal leaks (basically almost always there), as well as them being bullet proof (once drove mine in traffic with a radiator leak and super overheated it with no damage). The only thing I can add is that along with being bullet proof, the cost of parts for them is ridiculously cheap and most mechanics find them extremely easy to work on. Lastly, the one negative thing about them that was left out is how bad the MPG is both city and highway.

My radiator blew up, bad. I was a few miles from home when it went, coolant all over the windshield, white smoke pouring out and the temp guage pretty much pinned in the red. Got it home, had the radiator replaced and checked over, still runs like a champ with 165,000 miles on it. Part of the reason I haven't gotten a newer jeep is the V6 they put in it, other part is I can't afford one....lol.. Gonna drive my '03 Rubicon until one of us dies. :) Ps. Nice video, just subbed.

Have a 2004 Grand Cherokee, 452,000 miles, still running strong, all original, including the 42RH transmission

I LIVE IN THE GREAT STATE OF TENNESSEE A LOT OF JEEP OWNERS HERE!BEEN TURNING WRENCHES FOR 53 YEARS COMING UP ON 70,SO HERE ARE THE FACTS!THIS MOTOR HAS BEEN AROUND FOR 77 YEARS!FIRST USED IN THE NASH 600 BACK IN 1946,IT WAS CALLED "SUPER 242"!NASH AND HUDSON MERGED THEY BROUGHT KAISER JEEP,AMC BOUGHT THESE 3,THEN CHRYSLER BOUGHT AMC.THE CO.AMERICAN MOTOR CO.WAS WAY AHEAD OF ITS TIME,THEY HAD THE 1ST ALL WHEEL CROSSOVER ,,THE EAGLE THE DEVELOPED A/C,,ROTORS PADS,POWER WINDOWS AND LOCKS AND CRUISE,WHILE FORD AND CHEVY WERE TWILDING THIER THUMBS.ITS A SIMPLE ENGINE BUT A BEAST THATS WHY I OWN A 95 Z J 26 YEARS OLD NOT A DROP OF OIL ON THE DRIVEWAY CLOSE TO 410,000!

Brother, you did your research. Great video.

I agree one of the best engines ever built! I've seen them with over 250k miles still running like a top. Take care of your shit and it'll take care of you. With this engine even if you don't take care of them they'll still keep running. Can't say the same for the rest of the drive train but that engine is like you said basically bullet proof! Great video!!

I got a 92. dont hit my head getting in and out. the wife died with a 2019 cadillac. I sold the cadillac and kept the jeep. inside armoralled with a cd player radio. I am good.

I had this engine in my Cherokee coupled to the Peugot 5 speed transmission. One day I was cruising at about 90 mph or a bit more. I looked down at my shifter and realized that I was still in fourth gear! No tachometer.

i’ve got me a 98 grand cherokee laredo 4.0l it’s gonna be my first vehicle i hope it lives up to all this potential i hear about it!

Can’t forget the 300 Ford straight six

98 ZJ. Current daily driver. 300k Motor has hard froze a couple times, overheated badly a few times. It is indestructible and I love it. Very solid bone stock veh off road as well. Loves to climb.

Looking at buying a 2005 4.0 for my daughter. I thought this video was truly excellent. Well done! Thanks and I just subbed.

So correct! I have gotten my engine hot where an aluminum block would just melt. I have done the Rubicon with no oil but yet it was synthetic coating that and got out of there that engine is Bulletproof amen.

On XJ number 6, this one has almost 300,000 miles on it.

I had an experience with the 2.5 4 cylinder. I dated a girl that drove the jeep everywhere wide open without fail. She complained about it not having a working heater for years and years, the jeep lived in Tucson az so a heater wasn't really necessary but proper cooling was but when the jeep moved to Missouri things changed. I eventually realized that no hot coolant was moving anywhere in the engine so I pulled off the water pump... It had a radiator leak years before so she kept adding super hard tap water from Tucson.... That water eventually plugged up the hole in the radiator and also completely corroded the water pump vanes all the way down to the shaft. That damn jeep drove around for years with no water pump, it was somehow cooling itself with simple convection all while be completely covered with mineral deposits. That was the most gutless vehicle I have ever driven but it had earned my respect to say the least.

I had 4 of them over about 20 years. 300,000+ miles. Cjs, tjs and cherokees. Best engine ever.

My 1991 has 379,886 on her. She sat for two years before I finally went and got her again. All she needed was a battery and she fired right up. And before I even got her, my uncle had her for 8 years when he was in college. The only thing he did to her in 8 years was ONE oil change.... She's still purring to this day. Suspension is basically gone though lol. Tbf, everything except the headlights is from the dealer.

The one other glitch you forgot was the noisy lifters. Lifter tick is super common with this engine. It doesn't do anything to reliability, it's just slightly annoying. I've had a few that have gone 300k miles with lifter ticking and never had any other problem with the motor.

I love my 01 JGC and runs like it is still new. I traded a ham radio for get mine because my black JGC was white with bird doo doo after it was parked under a tree for 3 years. I replaced the bald tires, replaced top hose, put new alt, replaced the Coil Pack, replaced the original plugs with 1/4 gap to new double platinum plugs, replaced front shocks and both frame bumpers during the last 4 years I’ve owned it. I replaced the valve cover gasket, adjusted the kickdown cable. I did remove the front passenger headlight to replace the radiator fan switch which is inside the front bumper by cutting a 5” panel on the top, then using duck tape to hold the panel in place, re-install headlight and overheat problem gone but boiled the coolant out of the reserve bottle 3 times before I figure it out. God, I love my Jeep.

My '98 wrangler was riding on black oil for about a year before a tech told me I needed to change it when I went in for a high idle. I would've probably never known something was wrong. It started and ran just fine and still does. I hope to see the day when I get to give it to my children.

Own a 95 4.0, bruh gotta swap it 😎 because I sent CL 6 to space 💪just passed Saturn

your points were right on Sir..............excellent. thx

Damn straight the 4.0 is the goat, got myself the very last jeep made with one, 06 wrangler

WJ 4.7 150,000 miles, never had an engine problem, bought it when it had 20,000 in it. Have had electrical problems, a/c problems, and door actuator problems, but engine is still alive and kicking.

I had both the 2.5 L and 4L. The 2.5 L had horrible horsepower. I had a 2000 Jeep TJ and I have replaced many components including the water pump. All these components were very easy to get access. Very reliable and only the very components needed to be replace. A lot more torq than the 2007 Jeep Wrangler

I used to have a Gremlin 77 with the 242 engine inline 6, indestructible twice I broke a rod and it kept going making clacking sounds, but running, it always ran really cold never failed sold it in 1994, ran with the guy I sold it and its still running, in good condition, (rust in the doors and hatch) but it is a damn tractor.

My sister owned a Jeep TJ X with the 4.0L. She ran it for 4 months with less than a quart of oil. It's still running good with 175,000 miles on it. It's been off road and rev'd hard. I own it now and it's a fun little offroader.

This 3 year old video showed up 8/27/23! As an inline 6 fanatic, I own a '96 Grand Cherokee with a 4.0 plus a '95 F150 with a 4.9. my two favorite inline 6's for all the reasons you've stated. Thanks!

I appreciate these engines also the new jeeps are complete junk,they look cool but i hate them

Engineer and Race Engine Builder for 40 years. How do I trailer my Drag Bikes to the track ? Jeep Cherokee 4.0 with almost 300k miles. T.S. RACING 🇺🇸💪🏍

I own a '98 4.0L XJ, a 1KZTE swapped 2nd Gen ('95) 4Runner and an '89 22re 1st Gen 4Runner. The 22re is hands down the most durable (and in terms of chassis strength the early Toyota frames absolutely Trump the Jeeps unibody and Wrangler frames by a large margin) but I love the Jeeps 4.0L too and its a TANK as well. We did 3000+ miles on a road trip around OR/WA/ID and over 900miles off-road and when I got back to Washington the water pump exploded and I was sure I cooked the engine... nope. $350 later shes running like a top. Sadly the Jeep Unibody chassis aren't as tough as the Engines.

Excellent video! I've just bought a '92 YJ with 175K miles; the rear main seal is leaking but apart from that it has zero issues. Looking forward for replacing the seal and drive it for years to come...

I have a 1996 XJ with 446k miles original engine.

It really is as great as you feel. I'm 61 and have, experienced and am experiencing the Chrysler 225 and two Jeep TJ 4.0s. The common denominator being the smoothness and legendary reliability of both of them. Man, my 2005 TJ always fires up immediately. I've got 33s on it, along with an overall 4" lift, so it's not great for using all six gears. I'd love to regear it, but not with the Dana 35s it has. So, 44s that are already geared for 33s is the plan. With only 76k miles on it, I think I'll leave it mostly alone for another year. After a 70 mile run to the range in 90+ degree temps, it will drip maybe 2-3 drops of oil in 2-3 days, and then stop. Local trips don't faze it. Love the 4.0 and it, along with a manual, was a must have.

Really nice to hear and see all the info I had questions on in one video. Thanks

Thank you! Recently purchased a 97TJ with a 4.0. Subscribed from Canada

Will you do tips and tricks on the cooling system?

i found a manual wrangler 4.0 with minimalistic surface rust. I'm planning on having it at my summerplace and learing how to build on it and offroad and go to the dock where my boat is. i'm really tempted. i'm only fifteen though. still i really am considering it

Awesome engines. I've got a '04 TJ Rubicon on 35" pitbull rockers, 4 low, 3rd gear is the sweet spot, gobs of bottom end torque, and usually enough speed in the gnarly trails. When its time for a rebuild might go with a Golen stroker kit.

My favorite as well. I've had 2 ZJs and 2 WJs all with the 4.0. 2 which I put over 330k miles on them. Love that motor!

8:30 "destroying these engines is basically impossible" Me sitting here watching this video wondering how the hell I blew up two motors in one week....

Yes the 4.0 is almost indestructible- back in the late 2000's when the government had their buyback program- dealers had to make sure the cars or engines would not be used again by breaking the engines most commonly by running them without oil. I know the Jeep dealers ended up having to pour sand in the 4.0's to get them to finally seize up. What a shame and sad.

I have a 05 Wrangler Sport with a 4.0 in it - and I've had so many issues with the damn thing.. but never the engine itself. I've replaced just about everything electrical, the fuel pump, radiator and thermostat but never had an issue with the actual engine - it's a beast

I’ve gotten water in my ‘88 4.0 while mudding a handful of times, it’s been over revved many times, been overheated past the end of the temp gauge once or twice, and has run on 5 and even 4 cylinders multiple times, all at over 230,000 miles. The ONLY issue I’ve had with it over 5 years is the original water pump going out, absolutely bulletproof.

282000 miles on my 4.0 I change the oil every 3000 miles no smokin and uses a quarter quart of oil in the 3000 miles. pennzoil 10w30.

I know this is an old video but I do love this engine as well, actually I just love 99% of all inline 6 engines. That said I just have to say I think Chrysler missed a huge opportunity when this engine was out that they never put it in the dodge Dakota. The low end torque, efficiency, and reliability it would have been a perfect match to be offered in the Dakota instead of the v6 or 4.7v8

I have a 98 4.0 with 410000 miles on it and it has never left me anywhere I didn't want to be left

Several years ago, I asked a 40 year engine rebuilder his choices for the 3 most reliable American made engines: 1: the small block chevy, especially the 307. 2: the 300 ford in-line 6, and 3: the 4.0. I just picked up a 04 WJ 4.0 Special Edition with 196K, ($1,500) and it runs perfect, strong and quiet. Uses no oil, leaks nothing and it's smooth as silk at 75 mph.