Difference between 2H and 4H AUTO on dry roads?

[lindaspins]

A fellow with a 4xe did an 80-mile road test, once in 2H and once in 4H Auto and compared MPG. 2H was 19.6 while 4H AUTO was 23.8 even though the Jeep people said their engineers found there is "really no difference".



The fellow acknowledged the 2H 80-mile trip was hilly while the other one was not. But a 4MPG difference?

He didn't say how he excluded the battery for these tests while, in a subsequent video, he said he depleted the battery to calculate MPH but that video was not a 2H vs 4H AUTO comparison.

As my vehicle won't be 4Xe, I kinda set his test aside.

Wrangler mileage is so variable anyway that it's really hard to pin down what causes differences. Variations in speed, cargo, wind direction, pavement-it all makes a difference. All I know is that if I had to pick one of our two Jeeps and sell the other, the 4xe would win every time.

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[Panda Mafia]

I have tested mine a few times. Always have similar mileage. Summer time weather obviously. Then again I don't care about mileage. Winter time if my gf driving the Jeep, it's safer, I feel better knowing that. Plus I have way too much fun with it in 4Ha on snow roads. My 4xe 95% of its life has been in 4H auto.

 

[Zandcwhite]

A fellow with a 4xe did an 80-mile road test, once in 2H and once in 4H Auto and compared MPG. 2H was 19.6 while 4H AUTO was 23.8 even though the Jeep people said their engineers found there is "really no difference".



The fellow acknowledged the 2H 80-mile trip was hilly while the other one was not. But a 4MPG difference?

He didn't say how he excluded the battery for these tests while, in a subsequent video, he said he depleted the battery to calculate MPH but that video was not a 2H vs 4H AUTO comparison.

As my vehicle won't be 4Xe, I kinda set his test aside.

Better mpg in 4A means you can throw his test in the trash. I doubt it makes much of a difference having the front axle engaged vs not in 2H, but any difference it does make favors 2H by simple physics. Neither JL we've owned has had 4A, so I don't have any real world experience, but why anyone would drive around in 4A spinning their front driveshaft needlessly in dry conditions is beyond me if 2H is an option. The wear difference will be as minimal as the mpg difference, but it still favors 2H. On a 392 I believe the Tazer can enable 2H but I'm not sure there.

 

[Ratbert]

I'm just trying to find out as much as I can before buying a Jeep which may be a 392 where I would have no 2H with which to compare to 4H AUTO. Curious, too.

If you're thinking about buying a 392 and any concerns about "does (whatever) impact mileage?" then you're looking at the wrong engine. The 392's mileage is absolutely horrific. That's not what people buy it for.

Note, however, that you can get a Tazer and enable 2H with the 392. That's intended for burnouts, however, and not for any perceived increase in mileage.

 

[kmmn]

In 4 auto, the front axle shouldn't engage until the transfer case senses slippage... then typically a viscous coupler engages the front output shaft and you're in 4wd. It's great for slick wet/snowy roads. I would have gotten it, but it wasn't available on the EcoDiesel

 

[Zandcwhite]

In my opinion/experience if you drive aggressively in a non-392 JLU on big tires your mileage is going to be pretty close to that of the 392 anyway. Our 2019 on 38s with the 2.0t got mid 16 mpgs on average and closer to 15 at freeway speeds. This mileage didn't change much when we regeared from 4.10s to 5.38s. That brick into the wind thing needs all the power it can get. Out 2022 with 35s and a 3.5" lift averaged low 14 mpgs and would drop into the 13s at freeway speed with 4.56 gears. Now with 39s is averaging high 13s. Now granted we do drive on the faster/more aggressive side, but with the 392s power to spare I'm guessing you'd actually be easier on the skinny pedal. Most guys seem to average in the 12-14mpg range on their 392s which is right in line with our 3.6L mpg. If you're concerned with mpgs I would not but a wrangler period. Can you hypermile an ecodiesel into the high 20s driving 10mph under the speed limit and drafting semi's everywhere you go? Sure. My buddy with an ecodiesel on 37s who drives like I do averages 14-15mpg on the way up to Tahoe. I'll just but gas and get to the wheeling destination asap, but to each his own.

 

[Zandcwhite]

In 4 auto, the front axle shouldn't engage until the transfer case senses slippage... then typically a viscous coupler engages the front output shaft and you're in 4wd. It's great for slick wet/snowy roads. I would have gotten it, but it wasn't available on the EcoDiesel

The drive shaft isn't engaged, but the fad is, which means the front driveshaft is spinning although under no load. Like I said the drag and/or wear will be minimal but they still exist.

 

[kmmn]

The drive shaft isn't engaged, but the fad is, which means the front driveshaft is spinning although under no load. Like I said the drag and/or wear will be minimal but they still exist.

Right, the drive shaft is still spinning and there is wear (I miss the old days of locking hubs)

 

[Zandcwhite]

Right, the drive shaft is still spinning and there is wear (I miss the old days of locking hubs)

I'm all for the push button convenience at this point in my life. Shift in and out of 4wd at any time? Push a button to disconnect the sway bar? Another button for lockers? Adaptive cruise control so I can just set it and go? Sign me up.

 

[Dyolfknip74]

The fad doesn't control when 4wd engages if 2wd is slipping. That's a function of the tcase.

 

[Zandcwhite]

The fad doesn't control when 4wd engages if 2wd is slipping. That's a function of the tcase.

True, but putting the tcase in 4A engages the FAD so that the tcase can immediately shift in and out of 4wd via the viscous coupling. 2H is the only mode in which the fad is disengaged.

 

[Dyolfknip74]

True as well. Some of the statements gave me the impression it was all FAD is all. Having finally fixed my tcase issues after 3 years of "Serv4wd" I am a little passionate about the POS 4auto tcase. (Which actually isn't a POS, lol)

 

[Zandcwhite]

True as well. Some of the statements gave me the impression it was all FAD is all. Having finally fixed my tcase issues after 3 years of "Serv4wd" I am a little passionate about the POS 4auto tcase. (Which actually isn't a POS, lol)

I don't live where it snows and if/when I head to the mountains looking to go snow wheeling I know I want full time 4wd, thus I've never owned a wrangler with the 4A. Extra complexity and wear parts that I have no need for.

 

[sunset]

If you're thinking about buying a 392 and any concerns about "does (whatever) impact mileage?" then you're looking at the wrong engine. The 392's mileage is absolutely horrific. That's not what people buy it for.

Oh, I know how impractical the 392 is.

If you're concerned with mpgs I would not but a wrangler period.

It's not that this is a deal-breaker but this is all new to me and I want to know what you guys know and I am here right now and y'all are so helpful and I am analytical to a fault...

My delving curiosity always makes me look overly-concerned. LOL. It's how I teach myself.

Note, however, that you can get a Tazer and enable 2H with the 392.

You're the second person who has said this. I can check into it to educate myself but my first thought is how I would shift into 2H given the pattern portrayed on the shift knob itself:

 

[sunset]

In 4 auto, the front axle shouldn't engage until the transfer case senses slippage... then typically a viscous coupler engages the front output shaft and you're in 4wd. It's great for slick wet/snowy roads. I would have gotten it, but it wasn't available on the EcoDiesel

Well, Jeep is saying the front axle in 4H AUTO is always engaged to some degree in anticipation of slippage and that engagement affects MPG.

The drive shaft isn't engaged, but the fad is, which means the front driveshaft is spinning although under no load. Like I said the drag and/or wear will be minimal but they still exist.

What he said.

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