2wd Vs Auto Mode, Mpg Difference?

[ls2alex]

As the title states, is there a difference in gas mileage between being in 2wd vs auto mode? My truck is a 2007 SLT Sierra (new body) with z71 package and 4x4 obviously.

Thanks in advance

[hrspwr]

I am not sure, but would think so as the front diff would be locked causing more drag.

[mhenshaw]

Yes it burns more gas

[nickvrebel]

I have seen people state that it takes about 2 mpg more. I can confirm that it does take more, but I have not run it long enough to get solid numbers.

[ls2alex]

I was wondering b/c I know it would affect the mpg if I was on 4wd hi, but on auto it's running on 2wd only and only sends power to the other two if it's slipping correct? So why does it use up more.

Sorry if my questions make no sense

 

Alex

[DwayneJ]

As stated in the first response at the very least the front diff being engaged causes more drag, more parts of the transfer case would also be active.

[sic lsx]

in auto. it is in 2wd untill it fills a tire slip And then kicks into 4wd. So if its dry out I don't see how.

[Matt_]

In auto mode, the front diff actuator engages the front diff. So instead of just spinning spider gears, the entire carrier and driveshaft will spin which creates a lot more friction; especially in the t-case where the clutch that activates the front driveshaft does have some load on it in "ready" mode. It's not completely "off".

 

So yes, you will see deceased MPG.

 

In some cases you will actually feel some slight binding during very tight turns in parking lots.

 

In short; Auto is not the same as 2WD, there's a lot more going on.

[ls2alex]

In auto mode, the front diff actuator engages the front diff. So instead of just spinning spider gears, the entire carrier and driveshaft will spin which creates a lot more friction; especially in the t-case where the clutch that activates the front driveshaft does have some load on it in "ready" mode. It's not completely "off".

 

So yes, you will see deceased MPG.

 

In some cases you will actually feel some slight binding during very tight turns in parking lots.

 

In short; Auto is not the same as 2WD, there's a lot more going on.

Oh ok, thanks man.for explaining it. I just thought it was like being in 2wd.

[Wires]

In auto mode, the front diff actuator engages the front diff. So instead of just spinning spider gears, the entire carrier and driveshaft will spin which creates a lot more friction; especially in the t-case where the clutch that activates the front driveshaft does have some load on it in "ready" mode. It's not completely "off".

 

So yes, you will see deceased MPG.

 

In some cases you will actually feel some slight binding during very tight turns in parking lots.

 

In short; Auto is not the same as 2WD, there's a lot more going on.

Oh ok, thanks man.for explaining it. I just thought it was like being in 2wd.

 

 

 

On my 5.3L it was only about 0.5MPG. It wasn't enough for me to not run auto all the time. You'll lose more in 4HI though. You'd burn more fuel if you're doing a lot of corners, since you have to fight the differential. But on the straight (ie highway), not much difference than 2HI