Using 4WD auto 24/7/365: any downside?

[jastevenson]

Hi all,

Is there any downside to always running the car in 4WD auto, even in the summer? I know I take a small hit on fuel economy, but what about long term durability? Not sure if I am wearing down the system prematurely by doing this.

 

[1500V8]

Hi all,

Is there any downside to always running the car in 4WD auto, even in the summer? I know I take a small hit on fuel economy, but what about long term durability? Not sure if I am wearing down the system prematurely by doing this.

I use it more often than not- not really seeing a difference in MPG. I would like to hear what other folks are doing- saying about 4auto.

 

[LITTLEREBEL]

Isn't the TRX all time 4wd?

 

[kdoublep]

I run 4auto when it's wet. No issues or odd noises. Have run it dry but not for extensive period.

 

[Royalist_Ram]

Isn't the TRX all time 4wd?

It is a permanent 4wd setup

 

[OldMarine]

Think of 4wd Auto as 4 wd " standby". I leave mine in 2wd until I think I might need otherwise, but I don't see how it would hurt anything, otherwise the manual would advise not too.

 

[Richard320]

Shouldn't do a thing. The '95 Cherokee I replaced had no axle disconnect and no hubs. If the car was moving, so was the front diff and driveshaft. 270,000 miles and I never did a thing to the front axle but change the oil a couple times.

 

[Royalist_Ram]

There is no downside to running 4wd Auto all the time. I do the same thing. 4wd Auto is in 2WD (RWD) almost the entire time and will only switch to a 4WD configuration when it needs to (detects slippage, loses traction etc.). There is no loss in mpg because of this, because again, it will be in a 2WD setup the majority of the time, so long as you don’t drive in heavy rain/snow every day of the year. A lot of people have misconceptions about it and claim loss in mpg over just being in normal 2WD all the time; as well as parts wearing abnormalities. I call bs, unless the truck is switching over a lot, more than say usual.

 

[jimchi]

There is no downside to running 4wd Auto all the time. I do the same thing. 4wd Auto is in 2WD (RWD) almost the entire time and will only switch to a 4WD configuration when it needs to (detects slippage, loses traction etc.). There is no loss in mpg because of this, because again, it will be in a 2WD setup the majority of the time, so long as you don’t drive in heavy rain/snow every day of the year. A lot of people have misconceptions about it and claim loss in mpg over just being in normal 2WD all the time; as well as parts wearing abnormalities. I call bs, unless the truck is switching over a lot, more than say usual.

The following info is from this forum, I have not verified it myself:

The DT has axle disconnects that are disengaged in 2WD and engaged in all 4WD modes. When engaged, these axle disconnects force the front wheels to turn the front diff, and therefore the front driveshaft. When turning these additional components, a slight reduction in mileage occurs.

 

[Royalist_Ram]

The following info is from this forum, I have not verified it myself:

The DT has axle disconnects that are disengaged in 2WD and engaged in all 4WD modes. When engaged, these axle disconnects force the front wheels to turn the front diff, and therefore the front driveshaft. When turning these additional components, a slight reduction in mileage occurs.

Exactly, if those disconnects are occurring for long periods of time, ie several minutes, of course you’ll get a slight mileage disruption just as if you’ll be in 4wd Hi throughout a trip for example. But say you’re in 4wd auto and you take a turn too fast and slip on a slick surface and your wheels lose some traction and it goes from 2WD to 4wd Hi, then the mileage dropping from that incident will be so minuscule you won’t even notice; even if that happens multiple times on your trip. Now if you’re in 4wd Auto and in some deep snow and it’s disconnecting a lot, then yeah you’ll get a mileage drop for sure.

>>> Refer to manual.

 

[jimchi]

The following info is from this forum, I have not verified it myself:

Exactly, if those disconnects are occurring for long periods of time, ie several minutes, of course you’ll get a slight mileage disruption just as if you’ll be in 4wd Hi throughout a trip for example. But say you’re in 4wd auto and you take a turn too fast and slip on a slick surface and your wheels lose some traction and it goes from 2WD to 4wd Hi, then the mileage dropping from that incident will be so minuscule you won’t even notice; even if that happens multiple times on your trip. Now if you’re in 4wd Auto and in some deep snow and it’s disconnecting a lot, then yeah you’ll get a mileage drop for sure.

>>> Refer to manual.

I think you are misunderstanding the function of the axle disconnects. They are a separate component from the transfer case.

• 2WD: Front axles disconnected from front diff, transfer case unlocked
• 4WD Hi/Low: Front axles connected to front diff, transfer case locked
• 4WD Auto: Front axles connected to front diff, transfer case locking computer controlled

So while in 4WD Auto mode, the front wheels are turning their respective half-shafts, the front diff, and the front driveshaft up to the transfer case. When the computer detects a speed differential between front & rear axles, the transfer case is commanded to lock, thus providing 4WD capability.
While in 2WD mode, the front wheels are turning their half-shafts up to the axle disconnects. The parasitic drag from turning the front diff & front driveshaft is no longer present (as in 4WD Auto mode), and therefore a mileage increase is observed.

 

[Royalist_Ram]

I think you are misunderstanding the function of the axle disconnects. They are a separate component from the transfer case.

• 2WD: Front axles disconnected from front diff, transfer case unlocked
• 4WD Hi/Low: Front axles connected to front diff, transfer case locked
• 4WD Auto: Front axles connected to front diff, transfer case locking computer controlled

So while in 4WD Auto mode, the front wheels are turning their respective half-shafts, the front diff, and the front driveshaft up to the transfer case. When the computer detects a speed differential between front & rear axles, the transfer case is commanded to lock, thus providing 4WD capability.
While in 2WD mode, the front wheels are turning their half-shafts up to the axle disconnects. The parasitic drag from turning the front diff & front driveshaft is no longer present (as in 4WD Auto mode), and therefore a mileage increase is observed.

The drag is a factor correct, and your explanation is spot on but the change in mpg’s is so minuscule, day to day you won’t notice any real difference compared to sticking it in RWD all the time. I’ve tried this with my trucks, I noticed no real difference in MPG’s both via the dash and real world calculation. I live in the snow belt, and for half the year keeping it in 4wd Auto is kinda necessary and our HD doesn’t even have it, and it’s a pain.

Also, fun fact there are 3 types of parasitic drag, some are worse than others and will cause greater airflow issues resulting in higher mpg loss; pilot here.

 

[1500V8]

I think you are misunderstanding the function of the axle disconnects. They are a separate component from the transfer case.

• 2WD: Front axles disconnected from front diff, transfer case unlocked
• 4WD Hi/Low: Front axles connected to front diff, transfer case locked
• 4WD Auto: Front axles connected to front diff, transfer case locking computer controlled

So while in 4WD Auto mode, the front wheels are turning their respective half-shafts, the front diff, and the front driveshaft up to the transfer case. When the computer detects a speed differential between front & rear axles, the transfer case is commanded to lock, thus providing 4WD capability.
While in 2WD mode, the front wheels are turning their half-shafts up to the axle disconnects. The parasitic drag from turning the front diff & front driveshaft is no longer present (as in 4WD Auto mode), and therefore a mileage increase is observed.

Okay, that said- would I be better off with 4H rather than 4auto in snow and ice? I am currently using the 4auto for snow and ice. For some reason, we got a week of Arctic weather and the South is experiencing heavy snow, ice and "bone-chilling" temperatures (temps at 0-10 degrees with wind chill makes them negative readings). We usually don't have any snow or ice, but this year, we got lucky- NOT! Right now, it is a balmy 7 degrees and the low tonight is 0.

 

[GerryS]

I use 4H when there is a constant layer of snow and /or ice. 4H needs to have some slippage at the wheels to prevent any binding when the wheels are turning at different speeds.

I use 4Auto when the roads mostly provide traction (wet or dry) but there may be intermittent patches of snow and ice on the road.

I use 2H when the roads are just wet or dry.

That's just what I do.

Gerry

 

[mikeru82]

I keep mine in 4wd auto pretty much year round now. Since I have a locking rear diff, it basically acts as an open diff when not locked. When accelerating hard I was getting 1 wheel spin. So to avoid this I started keeping it in 4wd auto. It's been working great for that. And of course it helps with traction now that it's winter. It won't hurt anything to run it full-time.