Explain to me how towing in 4WD yields BETTER gas mileage than 2WD?

[itsdchz]

I am very curious on why, when towing my 4500+ lb trailer, I usually get 9.5-10 MPG, BUT if I tow the same trailer, on the same path in 4WD, gas mileage goes to the standard 13.5 MPG that I average city/hwy when NOT towing the trailer.

Explain to me how this is so..

BEFORE you FLAME, read on:

Last year towing my 18 ft. 2000 lb. trailer to Big Sur, we average 10.5 MPG 2WD- to and from Big Sur.

This Year towing 27 ft. 4500+ lb trailer, 2 separate occasions, 9.5-10 MPG 2WD
Most recently
-Going to Tahoe, 2WD- 55MPH Highway, slower mountain roads/snow/rain, 4WD in mountains/snow/rain AVG 10.5 MPG

However, in the heavy snow conditions, WITH chains and 4WD through mountains (SLOW), then - chains removed, but 4WD 3/4 trip back for lower elevations snow, and heavy rain most of the way 13.5 MPG. 55 MPH Highway. As soon as rain stopped, I kicked it into 2WD, and IMMEDIATELY gas mileage starts taking a hit back down to 9.5-10 MPG.

What is the logic around this? Cruising same MPH on Highway, 55 MPH, 2WD vs. 4WD, 4WD yields BETTER Gas mileage... What am I missing?:ybrick:

 

[Marcocopuffs]

I am very curious on why, when towing my 4500+ lb trailer, I usually get 9.5-10 MPG, BUT if I tow the same trailer, on the same path in 4WD, gas mileage goes to the standard 13.5 MPG that I average city/hwy when NOT towing the trailer.

Explain to me how this is so..

BEFORE you FLAME, read on:

Last year towing my 18 ft. 2000 lb. trailer to Big Sur, we average 10.5 MPG 2WD- to and from Big Sur.

This Year towing 27 ft. 4500+ lb trailer, 2 separate occasions, 9.5-10 MPG 2WD
Most recently
-Going to Tahoe, 2WD- 55MPH Highway, slower mountain roads/snow/rain, 4WD in mountains/snow/rain AVG 10.5 MPG

However, in the heavy snow conditions, WITH chains and 4WD through mountains (SLOW), then - chains removed, but 4WD 3/4 trip back for lower elevations snow, and heavy rain most of the way 13.5 MPG. 55 MPH Highway. As soon as rain stopped, I kicked it into 2WD, and IMMEDIATELY gas mileage starts taking a hit back down to 9.5-10 MPG.

What is the logic around this? Cruising same MPH on Highway, 55 MPH, 2WD vs. 4WD, 4WD yields BETTER Gas mileage... What am I missing?:ybrick:

Because you're driving slower?

 

[e60ral]

Tires, tire pressure, speed, how constant the speed was, grade, mistake or mis-remembering, etc...

 

[itsdchz]

Because you're driving slower?

55 MPH averages taken in both 2WD going up and 4WD coming back. Over 120 miles going 55MPH. 2WD 10 MPG, maybe 10.5MPG at best. 4WD 13.5 MPG.

Same stretches, same speeds there and back.

 

[itsdchz]

Again,

Same route taken-

Same Speed
Same Tires
3 Days apart

only difference was 4WD on highway for 120 miles vs 2WD for 120 miles, otherwise route was identical and conditions nearly the same.

Also, did same stretch of highway previous year with 18ft 2000lb trailer and saw 9.5-10 MPG both times in 2WD.

 

[Beer.runner]

2wd=engine works harder=burns more fuel . Theres multiple purposes for 4wd in 4runners and this is one of them. It's like air conditioning for example, up to a certain point you can drive with the windows down but when you go faster, it's just built to be more fuel efficient to drive with the A/C on if you know what I mean. It's the same for all vehicles when it comes to towing.

 

[BobsTrail]

:crazy:

 

[1engineer]

2wd=engine works harder=burns more fuel . Theres multiple purposes for 4wd in 4runners and this is one of them. It's like air conditioning for example, up to a certain point you can drive with the windows down but when you go faster, it's just built to be more fuel efficient to drive with the A/C on if you know what I mean. It's the same for all vehicles when it comes to towing.

???^^^

OP, I don't know why you got the results you did because:

In a complete apples to apples test 4WD will yield a slightly less mpg average.

Something, speed, wind, barometric pressure, etc skewed your results.

Lastly, you cannot give any credence to short trips like yours because they will not be accurate. Now, if you pulled the trailer across the US one way in 2WD and came back in 4WD then you could compare results.
Too many variables to get accurate results in that short of a pull. Believe it or not rain makes a difference too!

FWIW I have towed 4500 lbs 600 miles in 2WD and did the same trip several months later in 4WD. Gas mileage was about the same but it did take a 1/2 mpg hit in 4WD. Still that was only 600 miles at roughly the same speed.
Sorry.

 

[Bourbonator]

2wd=engine works harder=burns more fuel . Theres multiple purposes for 4wd in 4runners and this is one of them. It's like air conditioning for example, up to a certain point you can drive with the windows down but when you go faster, it's just built to be more fuel efficient to drive with the A/C on if you know what I mean. It's the same for all vehicles when it comes to towing.

Not buying it. In part-time 4wd, engaging 4wd means more parts moving (than while in 2wd) which should mean more work on the engine, which would translate into worse mpg, not better, right?

My guess would be, since there was a three-day time difference, that prevailing winds changed to your benefit at some point while in 4wd.

 

[itsdchz]

???^^^

OP, I don't know why you got the results you did because:

In a complete apples to apples test 4WD will yield a slightly less mpg average.

Something, speed, wind, barometric pressure, etc skewed your results.

Lastly, you cannot give any credence to short trips like yours because they will not be accurate. Now, if you pulled the trailer across the US one way in 2WD and came back in 4WD then you could compare results.
Too many variables to get accurate results in that short of a pull. Believe it or not rain makes a difference too!

FWIW I have towed 4500 lbs 600 miles in 2WD and did the same trip several months later in 4WD. Gas mileage was about the same but it did take a 1/2 mpg hit in 4WD. Still that was only 600 miles at roughly the same speed.
Sorry.

Understandable... However... 120 miles (240 total) of straight highway 55MPH is a pretty solid test that SHOULD NOT see a 3 MPG average difference. I could see a variable of .5-1 MPG, but very odd that I noticed the gain in MPG, and the immediate drop when placed back into 2WD on the ride home.

 

[enapa]

Wait so we can drive 55 in 4wd? I thought that was too fast?

 

[itsdchz]

Not buying it. In part-time 4wd, engaging 4wd means more parts moving (than while in 2wd) which should mean more work on the engine, which would translate into worse mpg, not better, right?

My guess would be, since there was a three-day time difference, that prevailing winds changed to your benefit at some point while in 4wd.

Actually, drive there had less winds than coming back, AND I was in heavy headwind and crosswind on drive back.

I get it, not buying it. It happened, I experienced it, even had my wife look at the numbers. compared GPS to miles driven, to miles to go, and in 4WD miles to empty stayed accurate to the GPS, whereas in 2WD, the miles to empty dropped faster in relation to miles to destination.

We also did real time numbers from the ScanGauge II AND manually at the gas station when we fueled up both times... I know weird, and I am lying...

 

[itsdchz]

wait so we can drive 55 in 4wd? I thought that was too fast?

4wd high

 

[Marcocopuffs]

Curious. Did you do a pump and mileage calculation or did you use the counter on the dash?

 

[enapa]

4wd high

I know you meant 4hi. I just thought that 45-50 was the max?

 

[itsdchz]

Curious. Did you do a pump and mileage calculation or did you use the counter on the dash?

As stated above, we used very method to see variance.
Pump and manual calculation
Dash
GPS miles to destination, vs miles to empty
ScanGauge

We noticed the difference and it was very obvious.

 

[1engineer]

Understandable... However... 120 miles (240 total) of straight highway 55MPH is a pretty solid test that SHOULD NOT see a 3 MPG average difference. I could see a variable of .5-1 MPG, but very odd that I noticed the gain in MPG, and the immediate drop when placed back into 2WD on the ride home.

You asked, I gave you an answer. 120 miles or even 1200 miles is not a pretty solid test. It's an anomaly, nothing more, nothing less. A curious talking point, sure, but definitive result? Hardly. Again, sorry but that's the truth.

 

[itsdchz]

You asked, I gave you an answer. 120 miles or even 1200 miles is not a pretty solid test. It's an anomaly, nothing more, nothing less. A curious talking point, sure, but definitive result? Hardly. Again, sorry but that's the truth.

Thank you for your responses

 

[BLACK-FL4RUNNER]

Just thinking out loud here...

Maybe when it's in 4wd it locks out the overdrive, which could actually cause less strain on the engine when pulling a heavy load?

 

[itsdchz]

Just thinking out loud here...

Maybe when it's in 4wd it locks out the overdrive, which could actually cause less strain on the engine when pulling a heavy load?

I tow in S4 no matter what. Leaving it in D causes the transmission to hunt and causes the transmission to heat up. Your logic is right, however, this wasn't a factor in the drive.