*ACHIEVED YES!!* I am trying to get 23 mpg to no avail

The demand side (energy requirement) will tend to favor a steady speed I think (assuming average speed is a constant), so long as you don't need to use the brakes at all. The wild card is how efficient the engine is at different loads.

It definitely feels more efficient to let speed drop on the uphill, but I doubt it really is.

 

Flat terrain yes, steady speed is king, but when grade increases, I think you lose more energy trying to maintain that steady speed vs accelerating a little beforehand and start bleeding your speed as you begin the climb. Mine feels like she starts to labor when speed drops below 55 going uphill. (<--This is when i butcher the ascend). Around 52 is when she feels really tired and torque converter lets go.

When doing freeway speed on rolling hills, I find it easiest for the truck to vary speed between 50 and 60. Downhill, I'd let her steady 55 or if it's steeper, she accelerates to 60 and when I'm in the valley, I input a little bit more pedal and let her slowly bleed speed all the way down to like 52. If I can time it properly, she is like a rollercoaster and transmission holds gear without straining the motor at all!

I've been just contemplating about this scenario if I'm getting enough efficiency by cutting gas going downhill or like Mr.Punishment mentioned earlier, to keep steady pedal. 4.6L is so strong that keeping pedal while descending, she would easily gain 65 or maybe even 70 and thats where mpgs might fall off? I can tell above 60, she's pushing air harder than necessary.

Ah, life problems....

 

I find it easier to just drive and enjoy the scenery

 

I get that it "feels" more efficient to bleed some speed going up rolling hills, because the truck labors less. But that could be deceiving.

Looking at it solely from the energy-demand side, for rolling resistance and hill climbing it makes no difference how fast you go; energy is the same over the same distance. For aero drag though, energy increases with speed, so the slower you go the better. Varying the speed at all vs steady, will increase the total energy requirement. Meaning... if an average speed of 65 mph from point A to B is your parameter, then varying between say 55 and 75 is going to require more total energy than maintaining 65... even with hills.

So the moral of that story is... just put it in cruise control. It's easy and probably close to optimal.

But there are a few caveats. If coasting downhill in 6th exceeds your speed setting then the truck will downshift and engine brake. That will obviously not be ideal for mpg... but if you exceed the speed limit on the downhill, you'll need to brake anyway. Also, there are variabilities in the supply side... like, I don't know what the engine's efficiency curve looks like. Does it take more or less than 2x the fuel at 100hp vs 50hp? How about 200hp? etc. I can think of reasons why it might be more efficient at higher power, because there is less throttling. But there are other things like the need to shift going uphill that will surely bleed some energy.

If you have a representative stretch of road around with little traffic, you might be able to test this. It will take some hours though, and you may find that traffic variability is still too much to get reliable data.

 

That's interesting, even if somewhat counterintuitive to my limited understanding. I don’t have cruise control or the mpg gauge on mine, but trying cruise control in my other car, mileage display showd a drop by a very heavy margin if the car is trying to maintain the speed going uphill. She would usually downshift and rpm rise another 500 or so and mpg is tanking.

 

Use an OBD app to monitor engine load and injector duty. Use whichever tactic to keep those values low.

 

Of course. But you'll have to make up for it elsewhere if you let speed drop on the climb, and it will "feel" better only because you've avoided the noise and vibration of the high powered segment.

The total energy demand to get from A to B in X minutes is just simple physics. Locking speed at the average takes the least total energy, even with hills. The supply side (the engine and drivetrain) is more complicated, but I think there is a small improvement in efficiency at higher power levels as well, which would also favor maintaining speed up the hills.

 

It has to be more efficient to recoup your speed on the downhill than to downshift to maintain it on the uphill then brake to maintain it on the downhill.

 

I already said that.

 

I used to do hypermiling. After saving like 2 miles worth of gas per tank for all the trouble, decided I might as well have fun driving "safely". On the other hand, if Vin Diesel rear-ends you, he's almost always at fault. Just maintain good insurance ig

 

Gang, saving 2 miles to a tank isnt hypermiling. That's margin of error. Now, let's crank some numbers:

I usually fill up when there's about 18gallons used on my tank. (It leaves about 1/4 of tank remaining.)

#1. 17mpg.
This is my personal "feel good idiot" driving. 17mpg X 18gal = can travel 306mi.

#2. 20mpg.
This is my typical calculated economy. 20mpg X 18gal = can travel 360mi.

Savings of 54miles per tank. That's over 2.5gals worth of fuel saved every fill-up.

#3. Hypothetically I hit 22mpg this time.
22mpg X 18gal = can travel 396mi.

396mi - 306mi = 90miles worth of extra miles. This is hypermiling vs idiota driving.

 

Lol... it was hyperbole bro
And I never saw *that* kinda mileage change! Good on ya!

 

Sorry gang, didn't realize you were kidding. I take mpg's very seriously.

 

i don't have the bandwidth to take mpgs seriously

 

After my adventurous dwellings among eternal 3rd gen failure discussions came to end, I decided to powerdive back into mpg's.

Today's fillip:

487 miles / 22.11gal
Result:

MPG's.

This one is interesting. First part of the naked was highway driving and backcountry with traffic lights. Second part of the tank took me across vast rolling hills and valleys with some very disappointing city driving mixed in. I think I helped raise world temperature by 0.02degrees with my brake pads due to sudden red lights. Might be a record this time. Every second light turned red for me with no roll. It was heart breaking.

But nevertheless...end result was surprisingly positive. This was without AC, so it might not very for everyone.