2H vs. 4H Auto Efficiency Shootout

One of the things that gets asked about and commented on a lot is the use of 2H vs. 4H Auto in the Jeep Wrangler 4XE. While there are many that believe that 4H Auto is inherently less efficient, the engineers at Jeep say there is little difference. In this video, I attempted a 2H vs. 4H Auto shootout. However, my numbers were a little skewed by the test conditions and 4H Auto actually did substantially better than 2H in my test. I will have to recreate the test at some point.

[@Trades46]

I don't even have a 4xe but very impressed with the amount of details you dug up on this car.

[@Wrangler4XEFans]

Thank you.

[@rogeliocasasbuenas9865]

Excellent consumption test with the traction system.

[@lanceskoog949]

If your Jeep 4wd system is similar to my Ram 4wd system, when 4 auto is engaged, the front axle is locked/both axles coupled together. In 2wd, the front axles are not locked, however the axles and pumpkin gears+drive shaft still spin as the axle ends are still connected at the wheel ends. There should be no discernable difference during regular driving as the transfer case clutch would stay unlocked and you are driving in 2wd still...just with the front axles coupled. The only fuel mileage savings we would actually see in a chrysler product would be independent wheel end actuators or manual locking hubs where in 2wd, the front axles are not engaged and the front axles, pumpkin and driveshaft would not rotate in 2wd (eg how Ford does it). In 4A, you may feel skipping/shuddering making turns if you have a limited slip front end. My ram is an open diff in the front so making turns in 4A is no different than in 2wd. All that being said, I'm old school and always run 2wd. I use 4A on the highway or city when there might be intermitent icy patches, however if I know its icy in the city and I will slip, I engage 4wd to also engage the transfer case clutch and hopefully therefore reduce slippage/wear on the transfer case clutch. That being said, in 4wd, the transfer case clutch is unlocked until there is throttle input. Once you apply throttle, the clutch engages. So if its icy, light throttle then normal will engage it with was feels like less slippage than just driving in 4A. Chrysler did this so when people drive in 4wd when they shouldn't, and let off the throttle, the T-case clutch unlocks and therefore unloads any binding on the 4wd system/components. Thats how the 4wd sytem on my 2013 ram w/ 4A works. I presume chrysler hasnt made any changes with the newer models including jeep.

[@princeminasi2802]

Well,my 4xe jlur is lifted on 37s and my mpg is 16.5 regular driving on pavements. I didn't see a single difference 2H vs 4H auto on pavement. On overlanding trips the difference is noticeable. As pumping gas going and getting smaller tank compare to other wrangler trims such as 3.6L I got a 4 gallon spare but I've never pumped 87 in my rig. 91 or 93 also never needed to use 4L

[@isidroayala123]

It's close by a few mpg but more consumption of oil & coolant for 4hi-low

[@KreeH2023]

As always, you ask interesting and important questions and come with with ways to answer them. This experiment is a good one and you noted factors which will add uncertainty to your results such as terrain, wind, temp, ... One additional factor to consider is the accuracy of the amount of gas to fill your tank. Gas pumps have some level of uncertainty including the point where your gas pump decides your tank is full (based on a change in vacuum). On my car, how fast the pump dispenses gas, the nozzle angle and how much pressure I apply to the nozzle, ... all seem to effect the outcome (I sometimes am able to add quite a bit more with a few clicks (without any spillage). So gas used values like 4.182g are probably closer to 4.2+/-0.2g (a total guess). This doesn't change the outcome of your test, ie. is 2H or 4H mpg different (20 vs 23mpg is a big delta) but it might make the mpg delta larger or smaller. Cheers!

[@Wrangler4XEFans]

Indeed. I alway fill up at the slowest that the little arm will allow. And I always give it one extra slow pull. But if I did this experiment in a controlled way but doing two trips on the same loop, I could return to the same gas pump too.

[@KreeH2023]

@@Wrangler4XEFans That would be good. On the 2H vs 4H subject, if the friction/loss/resistance is the same in both modes then you would think the mileage would be the same, but one thing I wonder about is the engineer/transmission programming for 2H vs 4H. I got the impression that in 4H, the 4xe actually accelerates faster than in 2H which might mean they use different programming which could also sway the results.

[@Wrangler4XEFans]

@@KreeH2023 Well, there's something I hadn't included in my thought part of the experiment. I was being pretty conservative on the throttle the entire time. So I'm not sure if that would come in to play or not. But now you've given me something else to think about.

[@KreeH2023]

@@Wrangler4XEFans I agree with your assessment that this would likely only really have an impact during acceleration and by avoiding acceleration events, it's likely a non-issue.

[@JuanManuel-kj8rz]

@@KreeH2023@wrangler4xefans Maybe it accelerates faster in 4h simply because it has better grip?

[@ghenry85]

I think doing the test on a preset loop of 80 miles would be best. So start out at a gas station and drive am 80 miles loop to the same gas station and measure. Also I wonder if driving on country roads or city would change the result. I think that the driving after dark would've skewed your milage aswell with the 4HA. Air is a bit cooler and perhaps a little more damp. Both help milage. The Wrangler 4xe is not my cup of tea, but I do enjoy your curiosity and candid approach. Keep up the good work.

[@Wrangler4XEFans]

I was thinking the exact same thing today. I need a loop. I try to do these little tests while I’m on trips. That way, I’m not burning gas just for a video. But to do it right, I need a loop to drive twice. I also thought about the cooler air too. It was 68 when I started the first part and 63 when I started the second one.

[@dennisl6198]

I would expect the MPG to be the same based on what I know about the 4 auto mode on a dry road. jeep MPG does really change when its hilly, so I'm sure that's why you saw that difference at the end.

[@jamestewell7721]

It’s the same as you said or a little less with 4wd auto if it actually ever needs to engage the 4wd as more parts to move and motivate. You don’t move more parts with less energy.

[@robsolf]

If anyone happens to know if/how much more metal is forced to spin full time in 4auto than 2H, they could make the case for/against the MPG argument. If the transfer case spins more metal with 4auto engaged but not "active"(detecting slip), then there may be an argument for a slight difference in MPG, but even then, we're not even talking the difference between MPG loss from a heavier driveshaft than a lighter one; very negligible. In my own personal experience, I haven't seen any difference.

[@robsolf]

YT keeps deleting it when I post it here, but I found an answer to my question. There is NO additional metal being spun when you set to 4auto compared to 2H. There's an electronic motor that moves a fork that engages the front axle whenever it detects slip. I posted a link to a vid that literally shows the guts of the system and how it works, but YT keeps deleting it.

[@Elk696]

Chris, you should do the experiment with a jeep buddy that has pretty much the same jeep as yours, you guys follow each other, one in 2h the other in 4h and then compare 👍

[@Wrangler4XEFans]

No doubt.

[@shiftintohigh5564]

Same exact road both tests. Same wind speed and direction. Now do Mid grade vs regular? lol, just kidding. Enjoying the Wrangler content. 👍👍✌️😎🇺🇸

[@Wrangler4XEFans]

I keep meaning to go fill up with premium and repeat this experiment.

[@JuanManuel-kj8rz]

Very interesting, but false, both tests have to be carried out in an identical section/loop. Please do it again correctly, we are waiting to see if there is a difference

[@Wrangler4XEFans]

I think both tests not only need to match but need to be longer. It’s on my to-do list.

[@JuanManuel-kj8rz]

@@Wrangler4XEFans Exactly, we are waiting expectantly for your best video 👏👏

[@paulfisher5902]

I have watched both of your mpg tests. I noticed that both tests showed worse mpg then the 2nd test. I worked assume that you are cleaning the system on the first leg. I always get better had mileage on a trip with the 2nd full up. Think about this variable when you do these tests. I do enjoy your videos.

[@Wrangler4XEFans]

I always clear them out multiple times when I do these. Now I’m going to have to pay attention to that variable too.

[@susanvo699]

Do you have to charge your jeep everyday? Your videos are helping me so much. I just got a 2024 Jeep wrangler and I am trying to understand the battery. I would charge to 100% and only drive to the store and back and I am already on 50% or less..

[@Wrangler4XEFans]

Yes, any time it’s parked, it’s plugged in.

[@danoesq2]

It's seems with 4 Auto you don't need 2H.

[@Wrangler4XEFans]

The 4XE was almost released without 2WD. But they decided to keep it toward the end of development.

[@MJXtube]

Hmm, interesting. I guess I would've preferred to see both tests on an identical stretch/loop of road, to eliminate that variable. Next time, I suppose.

[@Wrangler4XEFans]

Yeah. This experiment needs to be repeated on a duplicate loop for sure. I try to do stuff like this when I’m trips and not going out and just do them. But I’m going to have to find a way to do a controlled experiment.

[@SilverFoxCooking]

Myself, I would like to see an MPG test running in E-Save. One test set with E-Save set to maintain battery, the other test set set to charge the battery.

[@Wrangler4XEFans]

If you go back through my older videos, I’ve done several tests. I have an “MPG” playlist.

[@mowcowbell]

I've done it with my '23 Wrangler 4xe Sahara... about 20mpg on the highway at 70mph.

[@SilverFoxCooking]

@@mowcowbell So the mpg is the same whether you set it to charge the battery or maintain battery level? I would have thought there would be a difference. Heading to the Outer Banks in a few weeks. 750 miles each way. I was wondering what mode would be the best to use. I guess as soon as the battery is dead, I will switch to E-Save and set it to charge the battery.

[@mowcowbell]

@@SilverFoxCooking Don't let the battery go to >1%. Engage E-Save as soon as you get on the highway.

[@SilverFoxCooking]

@@mowcowbell That would make no sense to do that. I feel like you are missing the point. There are 2 modes to the E-Save. One mode saves the battery at its current level. The second one charges the battery. I just made a 25 mile trip with E-save set to Charge and gained 3 miles of electric range. On a full tank of gas I could possibly completely charge the battery 1 to 2 times, and in theory get 40-60 miles of electric range on a tank of gas. I don't want to just save the battery, I want to use it as much as possible without stopping to charge somewhere. In the E-save page it says the engine may be used to charge the battery, so I don't know if that will cut the MPG enough to nullify the use of the battery. I guess I will have enough miles on the trip to test it out.

[@rxtu7367]

First section is *slightly* down hill. 🤣 I notice this on trips. On the way there I’ll be impressed by my gas mileage. On the way back I’m disappointed. Lol

[@neilmiddleton9003]

Unrelated question; great channel by the way; that flashlight rig on your driver side roll bar, what is that??

[@basementdrumlab]

Fishbone off road.

[@Wrangler4XEFans]

Thank you, by the way.

[@senrusho]

You should get more regen braking in 4hi auto but otherwise I cant think of any reason why it would be that much better than 2h for MPG. I dont need to wring every single MPG out of it, I would leave it in 4ha even at a cost of a couple MPG and Jeep says it costs nothing so mine just stays in 4ha.

[@Wrangler4XEFans]

There isn’t more regen since all the regen comes from the P2 motor/generator in the transmission. Secondly, the front axel isn’t engaged in 4H Auto unless there’s wheel slip. If there’s wheel slip on deceleration, the anti-lock system would kick in. When that happens, the system bypasses the P2 motor/generator and uses the friction brakes.

[@senrusho]

@@Wrangler4XEFans If the front axel is engaged you are putting that inertia back through the P2 exactly the same as the rear. How sure are you that the front axle doesnt connect under braking? When my issues started with my front Ujoint I could feel the vibrations under only 2 scenarios in 2HA. 1) Hard acceleration and 2) braking. This indicates to me that the front driveshaft was under load in both of those scenarios in 4HA.

[@Wrangler4XEFans]

@@senrusho I need to catalog these videos but it’s in here somewhere. kzbin.info/aero/PLHXX4JfdDDmVNHxD3G9wLLNgb20Na_bkD

[@robsolf]

@@senrusho The only thing that would change the effectiveness of regen is something that would make the gen motor spin faster. If the front axle were engaged, it would turn at the same speed as the rear axle. 2 axles spinning at the same speed has no effect on regen charge. Think of a gas generator. It might have 1 gas motor spinning at 1500RPM, spinning the generator pulley and generating X amount of electricity. Add a second gas motor to the system with the same size pulley, spinning at the same RPM. The amount of electricity generated would stay the same.

[@senrusho]

@@Wrangler4XEFans Dan talks about it in episode 4 it looks like. He touches on a couple reasons why the tcase clutches would engage. He does not say that wheel slip is the exclusive reason for engaging the front axle. My anecdotal (though personal experience) evidence indicates the front drive shaft is under load under braking in 4HA.