3.7 engine reputation

[Jack Bryant]

Good afternoon my brothers. I have a question for most of you,and respect your opinions.
I have been building my 2002 kj. with a 3.7 engine with the advice of you guys that have been there done that. I have not skimped on price for safety reasons, and I won't the best parts for longevity. It has cost quite a bit but i think it is worth it regardless of what others say.
I have been ridiculed for putting money in something with a 3.7 engine that won't last very long. True it has a lot of miles but it still runs good.
I am asking for your opinions and if by chance the engine hoes bad is there a replacement or a suitable solution. Thanks for listening

 

[tommudd]

First yes there are replacment 3.7s available if that is your question
Next,
I don't care what type of engine, make, model, cubic inches etc that you can come up with they can be trashed to the point they are junk.
If treated right, regualr maintenance done, etc then the 3.7 holds up well
There are some who have 400-500,000 miles on their from various posts I have seen over the years
My 04 I bought new has over 232,000 miles and would drive it anywhere
The 03 and 05 were both bought used but came with all service records from day one , both one owners, I trust them all and hop that they will last another 23 years until I'm 90 LOL
Pay no attention to anyone who ridicule's your ride
its yours, you paid for it, you drive it and if you like it the heck with what they think
Example the 03, when I bought it in 2015 people thought I was nuts for installing a ( somewhat over 2000 dollar lift ) regearing, Moabs and larger tires, full leather Limited interior etc amounting to almost what I paid for it, the first week of ownership . But I knew I'd enjoy it more than anything else out there so I went with it and ignored the naysayers.
Almost 6 years later, over 80,000 miles, I have enjoyed every mile
So back to the 3.7 keep maintenance up, run it and enjoy it every day

 

[Jack Bryant]

First yes there are replacment 3.7s available if that is your question
Next,
I don't care what type of engine, make, model, cubic inches etc that you can come up with they can be trashed to the point they are junk.
If treated right, regualr maintenance done, etc then the 3.7 holds up well
There are some who have 400-500,000 miles on their from various posts I have seen over the years
My 04 I bought new has over 232,000 miles and would drive it anywhere
The 03 and 05 were both bought used but came with all service records from day one , both one owners, I trust them all and hop that they will last another 23 years until I'm 90 LOL
Pay no attention to anyone who ridicule's your ride
its yours, you paid for it, you drive it and if you like it the heck with what they think
Example the 03, when I bought it in 2015 people thought I was nuts for installing a ( somewhat over 2000 dollar lift ) regearing, Moabs and larger tires, full leather Limited interior etc amounting to almost what I paid for it, the first week of ownership . But I knew I'd enjoy it more than anything else out there so I went with it and ignored the naysayers.
Almost 6 years later, over 80,000 miles, I have enjoyed every mile
So back to the 3.7 keep maintenance up, run it and enjoy it every day

I too have spent more than I gave for it four times over ,but the more I do the better it looks

 

[tommudd]

I too have spent more than I gave for it four times over ,but the more I do the better it looks

I'll never, ever post how much went into and through the 04, bought new, lifted 4 times with different lifts, ( testing / upgrading etc )
3 different aftermarket front bumpers, two aftermarket rear bumpers, 3 aftermarket roof racks, two of them Rock Lizard, 2 different brands ( rock lizard and ALLJs ) of rock rails , gears, 2 sets of wheels after stock ones , 5 different sizes of tires , plus way too many other things LOL
all of that paperwork is hidden away from " prying eyes " LOL

 

[Jack Bryant]

I'll never, ever post how much went into and through the 04, bought new, lifted 4 times with different lifts, ( testing / upgrading etc )
3 different aftermarket front bumpers, two aftermarket rear bumpers, 3 aftermarket roof racks, two of them Rock Lizard, 2 different brands ( rock lizard and ALLJs ) of rock rails , gears, 2 sets of wheels after stock ones , 5 different sizes of tires , plus way too many other things LOL
all of that paperwork is hidden away from " prying eyes " LOL

I don't even keep records I have receipts for parts but I too have prying eyes . I am expecting the fun we will have to outweigh the cost.

 

[Bufftester]

I have a 2005 Rocky Mtn Edition I bought brand new. It now has 387,000 miles and still going. Compression is still in the serviceable range, still getting 19+ mpg. That includes half a dozen trips across the country and 5 North Dakotan winters. Biggest issue I've had was transmission at 235,000. Everything else had been pretty minor. All that with just the basic maintenance. Lots of folks laughed, and are on their 2nd and 3rd vehicles while mines still going 16 years later. As said above, if you like it, run it and enjoy it. It's not a very modern engine, but it's in the same class as the old Chevy 4.3l, parts are cheap, and it just runs.

 

[mercdudecbr600]

the 3.7 has a reputation of dropping exhaust valves due to a poorly designed valve retainer that doesn't allow the valve to rotate during combustion and then it overheats. PO of my '02 KJ had this happen, it's a common failure point (google is your friend) but I assume at some point they changed the retainer design. My KJ had a coast rebuilt unit installed so we'll see if it makes 100k without issue. So far, it just has a little valve noise that comes and goes - might be the valve not spinning on the retainer, just not sure. Other than that, the 3.7 is designed to be forded through high water and pretty much delivers (at the time) V8 power in a V6 package. It's torquey for offroading and gets "ok" mileage - acceptable in my book for a true 4WD.

IMO the engine is one of the least attractive components of the KJ. The overall vehicle design is very good - comfortable, good approach/departure angles, simple, good 2 speed transfer case, stiff, handles pretty well, brakes good, and has mechanical parts instead of electronic everything. Compared to today's jeeps, it feels like a dinosaur. But in a good way Has the important creature comforts without frills.

 

[mduclow]

Here is something I can tell you about these 3.7 engines, They DON'T like to be overheated. The valve seats in the valvetrain are known to dry out and crack, dropping a valve in the cylinder. This is almost always a result of high milage and a high temp overheat.

I would highly recommend installing a separate water temperature gauge, and even a transmission temperature gauge.

You will be amazed at what you see from a standalone water temp gauge vs the in dash factory gauge. Example: My factory gauge stays at the halfway point if the actual temps are between 175 and <230, this shown by my standalone water temp gauge.

DO NOT overheat this engine.

 

[04Liberty]

Valve seats are metal......they don't.......................dry out.............
What does happen is that the head is aluminum and if overheated, will expand more than the steel valve seat pressed into it and it might fall out.

The 3.7 is just like it's big brother the 4.7, a balancing act of getting it hot enough to burn off the condensation in the oil and prevent sludge build up vs not getting too hot so that it drops a seat on you.

 

[Doing10to20]

Just take care of it an is gonna last I got north of 214k hard miles and it runs great

 

[Johnny O]

Honestly, I have been very very impressed with the 3.7. Truthfully this is my first real foray into an engine system that uses electronics and coolant, however. I'll hit 179,000 miles sometime this week, 9000 of those since May 2021. (It is currently August 2021) Sure, you ain't gonna do 90 on the freeway all day towing a trailer and four other people with it, but it is not designed for that. Remember that the Liberty was intended to be a grocery getter for soccer moms that like to go camping on the weekends...

I honestly have not read much about poor reliability of this engine that could not be attributed to abuse and poor preventative maintenance. That is, like most other engines, if it is properly taken care of as used as designed, for the most part they will last. Sure, there are always exceptions, but we live in a time where non-mechanics whine and cry about things they don't understand and want nothing more than a lawsuit and/or someone to blame for their own inability to behave like responsible automobile owners.

As others have stated, Heat is the Mind Killer, to paraphrase Frank Herbert. Well, that and using the proper parts for the job.
Keep the plugs (the proper ones as suggested by the service manual and the Gurus around here) and COPs replaced according to mileage and driving style as per the manuals. Get that radiator professionally flushed and ONLY use the proper coolant! Oh, and dielectric grease is your friend, as are hood vents if you do lots of stop and go in traffic driving or towing/hills, off road etc.

Personally I believe 90% or so of the engine failure complaints on this system that litter the web can be attributed to the use of the wrong coolant, the wrong oil, and knuckleheads trying to drive a light all terrain vehicle like it is a MacLaren F-1. And, likely are by suburbanites that can't tell a 17mm crow's foot box from a 72 point ratchet... Well that and haters gonna hate, so I bet a bunch of that can be attributed to MOPAR freaks and Wrangle jockeys that are just gonna talk smack to make them feel their reproductive organs are large and useful...

As a reformed VW wrench jockey, I assure you that the size/make/year of the engine doesn't matter. Lubrication and coolant done right, followed by the right fuel and proper maintenance and they will last. My liberty was a rough running, heavily abused Heep that had been owned by the above type knuckleheads. I spent a total of 200$, followed the Guru advice on here and memorized the service manual maintenance schedules for my driving style and usage...and then drove it over 3k miles overloaded like I had a dozen bodies to hide in the desert just a few weeks later without any serious issues beyond a serpentine belt failure that is my fault as I knew it was old and I didn't put in hood vents prior to the trip...well that and my VW is a 58 with well over a million miles on it. 450k of those on the original factory 4 cylinder 1200cc 40ish HP engine which I still use for car shows and the like.


Whoops.....that's one heck of a rant. I shouldn't post pre coffee. :wink:

 

[mercdudecbr600]

Ya but by even relatively modern engine standards dropping valves is a big no-no. Kinda in the same realm as Subaru 2.5 h4 engine popping head gaskets at 120k. And they lost a class action lawsuit on that one.

 

[duderz7]

For every time tou hear about a dropped valve consider how many more have not. And like was said, it's due to neglect.

 

[Johnny O]

Agreed. Only two ways to drop a valve. Heat and lack of proper lubrication.

 

[mercdudecbr600]

Agreed. Only two ways to drop a valve. Heat and lack of proper lubrication.

Normally, yes. In this case, the early 3.7 had a faulty valve keeper design so the valve didn't rotate correctly. THus, it overheated and dropped. I have talked to at least 2-3 other (previous) Liberty owners that have had the same happen.

My limited KJ's 3.7 was babied by the PO and it dropped a valve at 90-95k. When it happens to you, it's not fun and it sticks with you. My beloved 01 Subaru Outback blew headgaskets at 120k even with the special Subaru coolant sealant being used throughout its life. To this day I avoid Subarus now due to the inherent design flaw of their H4 headgasket design.

 

[Johnny O]

Sure. Agreed.
All anecdotal evidence aside, facts are facts.
Still, I assure you a valve drop is a direct result of poor maintenance and and ‘ Murica style maintenance.

had to drive an air cooled VW four ****** on 3 cylinders for 2k miles with a beer bottle and JB weld…but you go ahead and do as social media tells you.exact same tech, 6years and billions of miles later.

valve blown is bad maintenance, period on a 3.7 Or any other engine.
Facts are facts.

feel free to go back to Instagram. Have fun with roadside assistance.

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