2WD or AUTO for better MPG?

[gilboyj]

Which is better? Anyone have any data collected?

 

[Micahsd]

2WD should be better. I don’t know the specifics but it engages the 4WD components but doesn’t actually send power to the front wheels until it senses slippage of some type (it’s more of a standby 4WD configuration where it’s ready to go until needed).

If you’re not driving on snow or a heavy downpour that might result in hydroplaning, it’s probably less wear and tear to leave it in 2WD until those conditions occur. The manual does a good job of explaining the differences between the modes.

I haven’t ran my ‘21 in Auto yet but would guess it should be similar to my ‘07 where it would get worse gas mileage in auto compared to 2WD. I don’t think it was that worse…maybe 2-3 gallon per mile difference.

 

[swathdiver]

Which is better? Anyone have any data collected?

You'll almost always get better gas mileage in 2WD. Use Auto for inclement weather on hard road surfaces such as during a heavy rain.

 

[TollKeeper]

A4WD activates the system, but does not engage the system. With it being activated, it will create more rotational resistance, resulting in lower fuel mileage.

 

[gilboyj]

2WD should be better. I don’t know the specifics but it engages the 4WD components but doesn’t actually send power to the front wheels until it senses slippage of some type (it’s more of a standby 4WD configuration where it’s ready to go until needed).

If you’re not driving on snow or a heavy downpour that might result in hydroplaning, it’s probably less wear and tear to leave it in 2WD until those conditions occur. The manual does a good job of explaining the differences between the modes.

I haven’t ran my ‘21 in Auto yet but would guess it should be similar to my ‘07 where it would get worse gas mileage in auto compared to 2WD. I don’t think it was that worse…maybe 2-3 gallon per mile difference.

So in 2WD it will actually switch to 4WD if it senses slippage?

 

[Micahsd]

So in 2WD it will actually switch to 4WD if it senses slippage?

No. In 2WD it will only send power to the rear wheels.

In Auto, it will be rear wheel drive also until it senses slippage then will engage the front wheels. But Auto mode will also spin more compments in the drive system so it should result in less mileage (which is why when there’s little chance of needing 4WD you’d want to run it in 2WD).

 

[GTNator]

No. In 2WD it will only send power to the rear wheels.

In Auto, it will be rear wheel drive also until it senses slippage then will engage the front wheels. But Auto mode will also spin more compments in the drive system so it should result in less mileage (which is why when there’s little chance of needing 4WD you’d want to run it in 2WD).

Agree, and you can even hear the difference between 2wd and Auto as Auto spins more gear.

 

[fozzi58]

This is 2WD. Over 50 miles I've been able to achieve 26.4mph as a best. People are usually astounded to hear that I average 22-23mpg highway mileage driving such a large vehicle with a v8.

I've been able to match it 2x's with headers, a CAI, and BBP tune. My average has dropped quite a bit recently because I just got the truck back..... with a Whipple installed so I am earning smiles per gallon at the moment

 

[Z15]

Snippets from GM service info explaining various 4wheel drives systems in use....

AUTOMATIC TRANSFER CASES
The last category is a combination of 4WD and On Demand AWD. These transfer cases have a 2HI, Auto-4WD, 4HI, 4LO and Neutral position and would fall in the general 4WD category. This transfer case has the operating characteristics of both an On Demand AWD and a Part-Time 4WD system depending on the mode selected. This transfer case uses a clutch pack to allow for a difference in speed between the front and rear axles in the Auto-4WD mode. In the 4HI or 4LO modes, there is no allowance for the difference in speed between the front and rear axles. An example of a vehicle with this would be a Sierra with a push-button transfer case with a 2HI, Auto-4WD, 4HI, 4LO, and Neutral positions.

If the transfer case is operated in 4HI or 4LO, it will behave as a Part-Time 4WD system. If it is operated in the Auto 4WD mode, it will behave like an on-demand AWD system.

The second category is an on-demand AWD. This type of AWD basically delivers torque only to a primary driving axle unless reduced traction is experienced. At that point, the system electronically or mechanically will apply torque to the other axle. Depending on the type of system, this can provide up to 100% of the torque to the axle with traction. These transfer cases use an electronically actuated clutch pack, a hydraulically actuated clutch pack, or a viscous coupling to allow for a difference in speed between the front and rear axles.

 

[Tyler M]

4WD auto is like driving with manual hubs turned in but with 4WD off so the CVs are spinning with the front differential.