Auto vs 2WD - MPG Question

JAshworth03 · December 8, 2020

All,

I can't remember what the final verdict was here. If I am in "Auto" mode do I lose any MPG benefits? I usually drive in 2WD mode, but with the roads getting a little worse with the weather, I was wondering if I should just leave it in Auto.

redwngr · December 8, 2020

Yes, slightly less mpg with it in auto as the actuator on the front axle stays engaged.

OnTheReel · December 8, 2020

It’s probably not a huge difference but it stands to reason that when in “auto” there is more drag (and wear). The axle shafts and front driveshaft are spinning in auto, everything is engaged and waiting for torque from the transfer case clutch.

newdude · December 8, 2020

.5mpg at best maybe? As long as it sees no traction loss, only 5% of power will flow to the front end and the diff will be engaged so the rear wheels are still doing 95% of the driving work.

Wiggums · December 9, 2020

Like others say, wear and tear. I keep mine 2WD unless it's pouring outside.

Rob Mugs · December 9, 2020

On a tangent, I leave it in 2WD unless I need 4. Guess I'm old school but on my older trucks, I'd leave the hubs (manual) unlocked until the moment 2WD failed me.

That said, maybe I'll give "auto" a try this weekend when we're supposed to see some snow

OnTheReel · December 9, 2020

9 minutes ago, Rob Mugs said:

On a tangent, I leave it in 2WD unless I need 4. Guess I'm old school but on my older trucks, I'd leave the hubs (manual) unlocked until the moment 2WD failed me.

That said, maybe I'll give "auto" a try this weekend when we're supposed to see some snow

Auto is perfect for light snow/ sloppy roads with mixed snow cover. I rarely even use 4 high.

Auto does allow some brief slip at first and you can still spin a bit, but you’ll never really get stuck unless it’s some nasty stuff.

Auto 4x4 is also my default drag race / gap the car alongside of me at a stoplight mode.

Duramaxsky · December 9, 2020

On a tangent, I leave it in 2WD unless I need 4. Guess I'm old school but on my older trucks, I'd leave the hubs (manual) unlocked until the moment 2WD failed me.

That said, maybe I'll give "auto" a try this weekend when we're supposed to see some snow

I used to be like that. Then a semi changed lanes and ran me into the median. It was a nightmare getting to the hubs in the deep snow. Once I did I was able to back right out. I left then locked in winter weather after that until trucks with hubs went awry.

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Rob Mugs · December 9, 2020

14 hours ago, OnTheReel said:

Auto 4x4 is also my default drag race / gap the car alongside of me at a stoplight mode.

Why not toss in 4 High for that? Seems like it'd be just a little more slippage and more wear on the clutch. It's only like 3-4 seconds to swap between.

OnTheReel · December 9, 2020

48 minutes ago, Rob Mugs said:

Why not toss in 4 High for that? Seems like it'd be just a little more slippage and more wear on the clutch. It's only like 3-4 seconds to swap between.

Eh, I’ve tested 0-60 a bunch in each mode. There’s no appreciable difference in times, get little-to-no wheel spin in either mode. For street fun especially, I just like auto. Can steer without fear, lol.

Rob Mugs · December 9, 2020

14 minutes ago, OnTheReel said:

Eh, I’ve tested 0-60 a bunch in each mode. There’s no appreciable difference in times, get little-to-no wheel spin in either mode. For street fun especially, I just like auto. Can steer without fear, lol.

LOL.. touche

I have made the mistake of forgetting to turn it off and then get the dreaded... "noooo ... I don't wanna turn"

Took it up to GLD for a few bone-stock passes. Hit a 14 flat but I think a ton of that is due to the speed cap at 98. FWIW, I also brake torqued a few passes and then just stabbed it. Stabbing knocked 2 tenths off

Edited December 9, 2020 by Rob Mugs

Duramaxsky · December 10, 2020

Eh, I’ve tested 0-60 a bunch in each mode. There’s no appreciable difference in times, get little-to-no wheel spin in either mode. For street fun especially, I just like auto. Can steer without fear, lol.

And with the clutch slip there is less chance of the front tires bending the tie rods and going full toe in. I know these trucks really don't have the power to do that easily but it can happen. It's common on Duramax powered trucks. Plus when crossing the slick crosswalk lines all the power going to the front end could break something. It's not as heavy duty as it's not intended to be the only one operating.

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Duramaxsky · December 10, 2020

LOL.. touche

I have made the mistake of forgetting to turn it off and then get the dreaded... "noooo ... I don't wanna turn"

Took it up to GLD for a few bone-stock passes. Hit a 14 flat but I think a ton of that is due to the speed cap at 98. FWIW, I also brake torqued a few passes and then just stabbed it. Stabbing knocked 2 tenths off

I was crossing the mountains in Southern Oregon and Northern California a few years ago. It was snowing hard. I was towing my travel trailer with my Duramax. The CHP chain enforcement check point made me chain up the trailer. Not the truck because it's 4WD. Just the trailer. Even though it has BF Goodrich all terrain TAs on it. I was not happy about it. When I stopped to take them off I forgot to take it out of 4WD. I didn't notice it until I got to LA. It was jumping trying to turn backing into the RV spot. As best I can tell it didn't hurt anything. Mostly freeway and it was raining hard the whole time.

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GMP · December 10, 2020

Even in auto front diff is still engaged. Will wear parts eventually. Brother in law left his in auto for two years blew out his front diff. Only use when needed.