Reliability of the Staright Six 4.0 - Jeep Wrangler Forum

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Old 12-26-2013, 11:59 AM   #1
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Reliability of the Staright Six 4.0

Due to job reasons, I need to pick up a second vehicle. I'll mostly do highway driving and lease road driving, which is not going to be good on my Challenger. Probably around 22,000 miles a year. One vehicle I've been considering is a 2005 Jeep Wrangler Unlimited. It's got about 70k on it right now. I was wondering how reliable that engine is, and the vehicle as a whole. I've mostly read good things about the engine, but mixed reviews on other things (sway bars, rotors, bushings to name a few).

Thanks in advanced.
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Old 12-26-2013, 12:14 PM   #2
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Isn't it the same AMC 4.0L that's been around since the stone age and is generally regarded as being bomb-proof?

There's something to be said about a platform that's been around as long as that one has. If it's stuck around, it's done so for a reason.

As a whole, as far as I know, the TJ's pretty darned reliable. But you don't just buy a Jeep. You adopt a Jeep. You make it a member of your family.

2010 Wrangler Sport - Dark Charcoal Peal - 6-speed - 3.21 - Katzkin
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Old 12-26-2013, 12:49 PM   #3
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It'd be a valued member, for sure. Just gotta make sure I don't adopt something that'll leave me stranded 200 miles from a real city.
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Old 12-26-2013, 12:52 PM   #4
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With a used vehicle, it's always hard to tell because you never know how it was treated by it's previous owner. 70,000 miles isn't really that much on modern drivetrains and it should still have a lot of life in it. The 4.0L AMC is a very reliable mill as long as it's cared for properly, like anything else. There are original owners running their TJs with the 4.0s at 200k+.
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Old 12-26-2013, 12:55 PM   #5
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The old 4.0 is pretty bulletproof. They develop a lot or torque at low RPM which makes it a better off road engine than what is in the newer Wranglers. Fuel mileage on those older engines was pretty bad though. I've had 3 vehicles with that engine, a 91 Cherokee, and a 95 and 99 Wrangler. My full size 1/2 ton 4X4 pickups got equal or better fuel mileage. I'd get about 14 city, 17-18 highway if I drove carefully. The newer 3.8 and 3.6 Wrangler engines are much better on fuel. I'm getting 18 city, 21 on the road with my 2010.

I think it would be a great choice if you intended to use as a 2nd vehicle and would see a lot of off roading. Not what I'd buy for a lot of highway miles
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Old 12-26-2013, 01:04 PM   #6
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I'd generally go about 200 highway miles to a county / lease road which will be gravel or dirt. When it rains is when it gets sketchy.
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Old 12-26-2013, 08:54 PM   #7
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The 4.0L is a pretty darn good engine for an off road vehicle.

The TJ is a good platform, but keep in mind that it is a Jeep and as such, it enjoys some maintenance. It isn't a gas up, change the oil twice a year, and drive for 250,000 carefree miles type of vehicle.
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Old 12-26-2013, 09:06 PM   #8
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They are great engines. If I could have a Jeep for a work rig I would do it in a heartbeat but, Im already addicted and any excuse to add another Jeep to the herd is fine with me.

I got 19 mpg with my 4.0 before the 35s. Now I get like 10.

Depending on write offs/whose paying for the fuel and all that it could be a great reason to get a wrangler. Especially if you need 4wd and can write it off... Even though I write off most of my gas, I bought a geo metro and started leaving my work van in town at my shop. It cut my gas bill from around 700 a month to like 150-200. Ugly little tin can car but the money saved covered the payments on my cummins and insurance on all 6 of my rigs.
91 Laredo, 4.0ho, TF999, Magnaflow exhaust, Yukon rear axles, Spartan Lockers, Posi locker, 3.5 inch springs, 1"MML, 1"BL, 1"shackles, trimmed fenders, raised flares, 35x13.50s.
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Old 12-27-2013, 01:52 PM   #9
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Overwhelmingly they seem to be great. That said, I bought my XJ with about 70k miles on it, and the 4.0 blew right after 100k. I'm assuming poor prior maintenance was to blame as I changed the oil religiously while I had it. Going to get 60k on my TJ in 2014, and hopefully having been in control of maintenance the whole time it'll last at least another 60k after that
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Old 01-05-2014, 12:27 PM   #10
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The 4.0 has a reputation of being solid, dependable and reliable for 200k plus. The driving you are going to be doing with it is where your wrangler will shine. The ability to have it as a second vehicle is going to help quite a bit with maintenance and other issues you may have. When my TJ was a second vehicle I had time to do repairs and other preventive maintenance myself. I had fun and saved a bunch of money. I daily drive my TJ now and I have to say I am really enjoying it but it likes money like strippers like oil tycoons.
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Old 01-17-2014, 02:17 PM   #11
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I owned a couple of Jeeps with 4.0s. I must say the engine was tough and long lasting but I can't say it was a great engine from a performance perspective.
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Old 01-17-2014, 02:43 PM   #12
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My wife had an XJ with 280K on it it was still running good when we sold it. We sold it because the body and interior was falling apart.
95 YJ 2.5 5 speed 33" Mud Rovers SOA
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Old 01-17-2014, 02:49 PM   #13
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The 4.0 is very solid. Easy to work on, reliable, torquey, and durable. It is also noisy and slightly underpowered on the top end. Take care of it and it will last a long time.

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Old 01-17-2014, 03:29 PM   #14
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great motor. id take a 4.0 over a ghetto pentastar any day.
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Old 01-17-2014, 04:33 PM   #15
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The 4.0 is a good reliable engine, but, 2005 and 2006 has the OPDA, which is a serious, oil pump drive gear issues! Chrysler/Jeep, re-positioned the seal starting in 2005, and now it is causing oil starvation.
If you purchase a year prior to 2005, then this issue doesn't exist!

I recommend that you go to the TJ Technical section of the Forum, and ask about this issue..........

Stay away from the 2005, and 2006 4.0..........
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Old 01-17-2014, 04:54 PM   #16
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I love my jeep and have gotten 148k trouble free miles out of it but if I had to commute 22k miles a year a TJ would be the last thing I would look at. Depending on how many times you have to make that commute a week, you are going to be uncomfortable and it will be loud compared to other 4 wheel drive vehicles. Yes, the Lj does have a longer Wheelbase and is a little more comfortable but its Your call, sometimes the lack of comfort is well worth owning the vehicle you want.

I know a lot of things, most of them are only correct in my own head...
Better to be judged by twelve then carried by six. I'm sure this is going to get me in trouble down the line
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