Is it me, or does the JT really struggle...

[jwilson2899]

I had 85, 87, 89 and 92 Comanche's and Cherokees. The 4.0 HO motor came into existence I think in 92 and they were great. The standard 4.0 before that was only marginally better then the 258.

Wasn’t there a GM sourced V6 too in that era, 2.8 I believe?
Man, that’s a long time ago……..

The XJ had the crappy carbureted 2.8 from 84-86, and the Comanche had it in 86 only. Terribly engine that’s really good only as a boat anchor. The 87-90 models got the 4.0 with Renix that was much better, but had lots of weird Renault/French twists to it. They switched the the 4.0 HO in 91 with a much more modern and better ignition and fuel injection system. Those are the best ones by far, which they continued with a few changes all the way through the end of the XJ, WJ, and TJ. I had an 88 Comanche, and it wasn’t bad, but the Renix stuff is definitely quirky.I would love to have a 91-92 Comanche with the 4.0 HO, but the prices have gotten so nuts it’s pretty much only a dream at this point.

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[steelponycowboy]

Wasn’t there a GM sourced V6 too in that era, 2.8 I believe?
Man, that’s a long time ago……..

Yes and the 2.8 sucked big time

 

[dcmdon]

Wish that I could use the Off-road + function when in 2WD, that really wakes up the engine with its different engine mapping.

On our Grand Cherokee with the same 3.6, Sport mode works really well on it.

I'm thinking Jeep don't want overheating issues or something on our Gladiators for everyday driving.

The engine makes heat proportional to the power you are asking it to make.

If you gear down a bit, like in sport mode, its not going to make appreciably more heat.

I was going to say that if you have an engine that doesn't make much torque, but loves to rev, then let it rev. Short of a "sport" mode, the next best thing is using the manual shifter to just drop it into 7th and leave it there when in hilly areas. Its not perfect. But letting the motor rev a bit won't hurt anything and will make it drive better.

Remember, the pentastar actually makes more power than the diesel. Power is the ability to do work. But the diesel makes more power at lower RPMs. So you need to let the pentastar spin to get much power out of it.

I've often thought that with cars that don't make much torque, they should under drive the tach by 1/2. So when its spinning 4000 rpm and making decent power, you will see 2000 rpm and think "wow, this thing is torquey". ha.

 

[Iamstubb]

I drive the M6 version with the 4.1 diff. You really got to wind it up, which is not necessarily intuitive. But that is where the motor is happy. Driving on hilly highways, 5th gear does great, maybe even the occasional 4th to keep speed. Driving in 6th is for those long flat stretches. Same engine in a Charger A8 is a totally different driving experience. Each has their place. Although I wouldn't mind if my JTR had a 3.6 turbo, a 5.7, or the 3.0 diesel in an M6. That would be fun. The 392 is overkill IMO.

 

[steelponycowboy]

I'm pretty sure the 3.0 has 100+ more LB ft of grunt than the Pentastar. Low RPM or not the diesel when working properly will out perform the 3.6 any day of the week.

 

[CerOf]

I'm pretty sure the 3.0 has 100+ more LB ft of grunt than the Pentastar. Low RPM or not the diesel when working properly will out perform the 3.6 any day of the week.

Gas 285hp 260tq
Diesel. 260hp 440tq

25hp difference but 180lbs more torque.
25 less hp is not a big deal. 180tq is significant.

I agree with steel pony.
(unless it’s 100 degrees going up a grade, lol.)

 

[dcmdon]

I'm pretty sure the 3.0 has 100+ more LB ft of grunt than the Pentastar. Low RPM or not the diesel when working properly will out perform the 3.6 any day of the week.

Which is where gearing and revving a gas engine makes up for the difference. But you need to be willing to rev it.

What moves the vehicle is torque at the axle.

A motor making 400 ft lbs of torque at 3000 rpm will with gearing provide the same torque at the axle at a given speed (power) as a motor making 200 ft-lbs of torque at 6000 rpm.

400 ft-lbs at 3000 rpm = 200 ft-lbs at 6000 rpm.

In this case I don't believe that the total "area under the curve" of the gas engine is as great as the diesel's. But its closer than you think.

Put another way. I used to race a 125 cc road race bike. It had 6 cubic inches and made 15 ft-lbs of torque. But because it could rev to 15,000 rpm, it made over 50 hp. It wouldn't even run below 6000 rpm.

I used to drag race it to practice starts because it was so finicky. My best time was 14.1 seconds at 97 mph. HP is what gets it done, if you are willing to flog the engine.

In day to day driving, when most of us don't want to flog the engine, the diesel makes MUCH more power between 1200 and 3000 rpm. So it feels much quicker. And is honestly more responsive because most of us don't want to drive down the road at 5000 rpm in the gas Jeep.

 

[NC_Overland]

The XJ had the crappy carbureted 2.8 from 84-86, and the Comanche had it in 86 only. Terribly engine that’s really good only as a boat anchor. The 87-90 models got the 4.0 with Renix that was much better, but had lots of weird Renault/French twists to it. They switched the the 4.0 HO in 91 with a much more modern and better ignition and fuel injection system. Those are the best ones by far, which they continued with a few changes all the way through the end of the XJ, WJ, and TJ. I had an 88 Comanche, and it wasn’t bad, but the Renix stuff is definitely quirky.I would love to have a 91-92 Comanche with the 4.0 HO, but the prices have gotten so nuts it’s pretty much only a dream at this point.

The 4.0l/Aw4 4 speed auto would feel like a boat anchor in a gladiator. XJs and MJs are super light.

 

[atxatxatx]

The engine makes heat proportional to the power you are asking it to make.

If you gear down a bit, like in sport mode, its not going to make appreciably more heat.

I was going to say that if you have an engine that doesn't make much torque, but loves to rev, then let it rev. Short of a "sport" mode, the next best thing is using the manual shifter to just drop it into 7th and leave it there when in hilly areas. Its not perfect. But letting the motor rev a bit won't hurt anything and will make it drive better.

Remember, the pentastar actually makes more power than the diesel. Power is the ability to do work. But the diesel makes more power at lower RPMs. So you need to let the pentastar spin to get much power out of it.

I've often thought that with cars that don't make much torque, they should under drive the tach by 1/2. So when its spinning 4000 rpm and making decent power, you will see 2000 rpm and think "wow, this thing is torquey". ha.

I understand what you are saying, and yes I do switch to "manual" mode and downshift in certain situations, and absolutely yes this engine needs to stay at above a certain rpm to be happy. Once its above that point it's not bad to drive.

My point was the Off-road+ has better engine mapping/throttle response (not just the shift points), same with our Grand Cherokee - the engine is more responsive in Sport mode.

 

[Trickster]

Yeah, my father had one in his S-10. That thing was a pooch. Even with a manual transmission, it was so sluggish, could have sworn there was a 4 cylinder under the hood.

Jeep back in those AMC days sourced parts from a few different manufacturers. In the 2.5 I believe the starter was from Ford.

 

[ShadowsPapa]

Jeep back in those AMC days sourced parts from a few different manufacturers. In the 2.5 I believe the starter was from Ford.

LOL - so did Ford, GM, MOPAR and others. (use parts from other companies)
Ford ownership of stuff was tricky as they bought other companies (Autolite) and then took certain aspects and made them their own, then turned around and sold Autolite again. So somewhere in the 70s, Autolite was no longer Ford.

MOPAR and GM used Kelsey-Hayes brakes. They all used Bendix brakes here and there.
AMC used Ford design starters beginning in the late 1960s - and when there were issues, AMC engineers resolved the problems, implemented the changes - and in at least a couple of cases, Ford copied the fixes and put them in starters for their own use.

Below is a starter I built/restored for a customer in Texas. He needed one to match the build date of his 68 AMX. I had the stuff to do it. Note the name and part number on the starter...........there were differences, such as the starter drive, for example. AMC's was different from Ford's

Where GM and Ford bought up the technology or even entire companies, or folded them into their own corporate messes, AMC didn't have the cash, so bought the products. They were also the first major company to use "just in time" manufacturing. They did make their own differentials to a point and then sold their designs to Dana in later years (that's why some Dana parts are the same as some AMC parts)

As far as the 4.0 - RENIX was not the most simple or reliable system ever made, but it was a leap ahead of many others, the best that could be done at that time in several ways.
The HO changes were more than minor.
For those of us doing the 4.0 swap into our cars, the best 4.0s to use were something like 94-96. The systems were simple to swap into other vehicles, for the most basic of swaps, only 5 wires were needed. (I merged a heck of a lot more when I did my swap) The split pattern cam made a big difference, they got rid of the EGR and dropped the knock sensor.

I've owned a lot of I6s, including several 258s (4.2L) and several 4.0 equipped vehicles.
I saw it said above the 4.0 was only marginally better? Not IMO. I beat the heck out of the 4.0 in my Comanche. Then later, I had a Cherokee with a better 4.0 and towed with it. Both would run circles around a 258, which in the 70s and 80s was no slouch, especially compared to other I6s.
Would I want one in something as heavy as the JT? Nope - the 3.6 blows the 4.0 away in towing abilities, mpg and other aspects of vehicle life.

I think we lose the phrase all too often than really needs to be inserted or implied when comparing things - and that phrase is "for its day".......... meaning "for its day" those I6s were superior to almost any other I6 engine, many running 200,000-300,000 miles untouched (other than basic tunes and maintenance)

The 3.6 is not underpowered and doesn't struggle when used for what it was designed to do.
Maybe too many of us grew up with cars that were made to run sub-5,000 or even sub-4,000 RPM.
I see running higher RPM still called "flogging" even in this forum - this thread. No, it's not. It's designed for higher RPM. We all (including me) need to get over our old ways.
You aren't flogging the 3.6 running over 3,000 or even 4.000 RPM. But you are flogging an older I6 at 4,000 RPM. Long stroke engines are great for low-end grunt, pure torque climbing up 5% grades in 3rd gear at 1400 rpm and accelerating but those same long stroke, high torque gas engines aren't great at 4,000-5,000 rpm.

 

[Trickster]

LOL - so did Ford, GM, MOPAR and others. (use parts from other companies)
Ford ownership of stuff was tricky as they bought other companies (Autolite) and then took certain aspects and made them their own, then turned around and sold Autolite again. So somewhere in the 70s, Autolite was no longer Ford.

MOPAR and GM used Kelsey-Hayes brakes. They all used Bendix brakes here and there.
AMC used Ford design starters beginning in the late 1960s - and when there were issues, AMC engineers resolved the problems, implemented the changes - and in at least a couple of cases, Ford copied the fixes and put them in starters for their own use.

Below is a starter I built/restored for a customer in Texas. He needed one to match the build date of his 68 AMX. I had the stuff to do it. Note the name and part number on the starter...........there were differences, such as the starter drive, for example. AMC's was different from Ford's

Where GM and Ford bought up the technology or even entire companies, or folded them into their own corporate messes, AMC didn't have the cash, so bought the products. They were also the first major company to use "just in time" manufacturing. They did make their own differentials to a point and then sold their designs to Dana in later years (that's why some Dana parts are the same as some AMC parts)

As far as the 4.0 - RENIX was not the most simple or reliable system ever made, but it was a leap ahead of many others, the best that could be done at that time in several ways.
The HO changes were more than minor.
For those of us doing the 4.0 swap into our cars, the best 4.0s to use were something like 94-96. The systems were simple to swap into other vehicles, for the most basic of swaps, only 5 wires were needed. (I merged a heck of a lot more when I did my swap) The split pattern cam made a big difference, they got rid of the EGR and dropped the knock sensor.

I've owned a lot of I6s, including several 258s (4.2L) and several 4.0 equipped vehicles.
I saw it said above the 4.0 was only marginally better? Not IMO. I beat the heck out of the 4.0 in my Comanche. Then later, I had a Cherokee with a better 4.0 and towed with it. Both would run circles around a 258, which in the 70s and 80s was no slouch, especially compared to other I6s.
Would I want one in something as heavy as the JT? Nope - the 3.6 blows the 4.0 away in towing abilities, mpg and other aspects of vehicle life.

I think we lose the phrase all too often than really needs to be inserted or implied when comparing things - and that phrase is "for its day".......... meaning "for its day" those I6s were superior to almost any other I6 engine, many running 200,000-300,000 miles untouched (other than basic tunes and maintenance)

The 3.6 is not underpowered and doesn't struggle when used for what it was designed to do.
Maybe too many of us grew up with cars that were made to run sub-5,000 or even sub-4,000 RPM.
I see running higher RPM still called "flogging" even in this forum - this thread. No, it's not. It's designed for higher RPM. We all (including me) need to get over our old ways.
You aren't flogging the 3.6 running over 3,000 or even 4.000 RPM. But you are flogging an older I6 at 4,000 RPM. Long stroke engines are great for low-end grunt, pure torque climbing up 5% grades in 3rd gear at 1400 rpm and accelerating but those same long stroke, high torque gas engines aren't great at 4,000-5,000 rpm.

That’s interesting and informative info Bill.
I am from that old school thinking of over revving engines on a daily basis. I can say I have not red lined a vehicle I owned for many years because of the fear of damaging it. Rental and company vehicles close, but I try not to abuse something that is making my life easier.
As the wife’s JT is still in its early stage of life and just getting out of its initial break in period, I will have to explore a more spirited range of its rpms.
I came pretty close to the rpm orange zone more than a few hundred shifts on my Durango SRT, but my wallet slowed me down before I got into some serious trouble.

 

[samd1351]

I'm, the 3.6 is okay. That is until I jumped in the 'stang the other day. Damn!!! Made my day rowing the gears on the way to Mexico. "Might" have hit triple digits on the entrance ramp. The JT is slug. But's supposed to be. Low end torque at low speeds. The mustang in the other hand, loves living above the 6000 rpm mark. Know your roll.

 

[Challenger85]

Lol I came from a 392 Challenger, Mojave is slow but honestly I like it that way. Make lame drive slower and more responsibly and relaxed. It speeds up when I need it too.

 

[ShadowsPapa]

Lol I came from a 392 Challenger, Mojave is slow but honestly I like it that way. Make lame drive slower and more responsibly and relaxed. It speeds up when I need it too.

It's a TRUCK. It's built for any conditions on or off road. As such it's not made to win races but to get there no matter what.
It's not a race car.
I tell people - regarding my two remaining classics - one goes anywhere, the other gets me places fast.
If I want to haul things or go where nothing else will go - I take the JT.
If I want to go fast, I take the Javelin.
If I want to really turn heads and have fun shifting and something I can park literally anywhere, I take the SX4.
Each has a purpose. A Swiss Army Knife does a lot of different things - but for that stubborn screw, get a real screwdriver.

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