Ford Transit USA Forum banner
1 - 20 of 28 Posts

·
Registered
2021 Ford Transit 250 HR Cargo AWD, 148" wheelbase, 3.5L Ecoboost, 10 speed transmission
Joined
·
10 Posts
Discussion Starter · #1 ·
Recently completed a 2,000 round trip while keeping the speed at a consistent 65. The outbound reported gas mileage was 18-19 mpg but the return was all over the place. 16 mpg was the average over the first 250 miles so thought it may be the gas. We only use top tier gas 87 octane. Then mpg rose to 17 and never got to 18.

What are others seeing? I recall a post that said they don't trust the mpg reported on the dash.
 

·
Registered
Joined
·
126 Posts
The MPG on the dash is pretty close. But you have to remember it's an algorithm. It's something that's calculated in real time on a continuous basis based on throttle position engine RPM etc. It's not perfect but it's close. I have a high roof and I've noticed pretty big mile per gallon differences based on whether or not it's a headwind or a tailwind... Also the octane number of the fuel doesn't affect its energy content. Won't affect your mileage. All the gasoline in the country is well regulated and chemically practically identical. Top tier simply means there are probably detergents and such added.
 

·
Registered
Joined
·
1,022 Posts
The MPG on the dash is pretty close. But you have to remember it's an algorithm. It's something that's calculated in real time on a continuous basis based on throttle position engine RPM etc. It's not perfect but it's close. I have a high roof and I've noticed pretty big mile per gallon differences based on whether or not it's a headwind or a tailwind... Also the octane number of the fuel doesn't affect its energy content. Won't affect your mileage. All the gasoline in the country is well regulated and chemically practically identical. Top tier simply means there are probably detergents and such added.
I don't know the details of how the MPG computer works, but on a 5000 mile trip it matched exactly the carefully computed mileage. It is quite likely that the computer knows the precise fuel flow, by monitoring injector pulses. Given how accurate it was on this 5000 trip, I suspect that is the case.

While it is true that octane rating does not affect its energy content, it is a false conclusion that therefore octane rating will not affect miles per gallon of fuel. Higher octane means the engine can run at higher compression (where a lower octane fuel would cause knocking) and higher compression can mean better efficiency, which can translate to more miles per gallon of gasoline.

That 5000 mile trip was from New York to Alaska, with the speed not exceeding 70 mph. Average mpg was 14.1

The vehicle is a SRW T350 with a 12 foot Unicell body, which is about 18 inches wider than a standard van.
 

·
Registered
E450 Wagon
Joined
·
505 Posts
FYI - In hot weather, or heavy loads, the EcoBoost motors all get better fuel economy. Because of the high cylinder pressures and intake temps, extra fuel is used to prevent detonation. You can even see the difference on the tailpipe. If I run 87 in my Focus during the summer, the tailpipe becomes completely black. On both that car, and my sister’s 3.5L EcoBoost explorer, it cost less per mile to drive using 92 octane, if the price premium is $0.30/gal. At 0.40 it’s a wash. In cold weather, the fuel economy difference isn’t as much, if any. It’s a little harder to tell since cold weather also adversely affects in-town fuel economy.
 

·
Registered
Joined
·
126 Posts
Maybe I'm missing something here. How are compression ratios being varied inside the engine? I mean the piston is moving up and down within the same volume... Does the 3.5 have variable compression ratio tech? I heard there was an Infiniti a couple of years ago that was playing with that but I didn't know Ford was....
 

·
Registered
Joined
·
1,022 Posts
Maybe I'm missing something here. How are compression ratios being varied inside the engine? I mean the piston is moving up and down within the same volume... Does the 3.5 have variable compression ratio tech? I heard there was an Infiniti a couple of years ago that was playing with that but I didn't know Ford was....
It would be better if some of the members here who understand this better than I do respond. I may have misspoke about compression, maybe it is ignition timing combined with valve timing. Regardless, I am quite certain that octane rating can affect both power and fuel economy.
 

·
Registered
Joined
·
126 Posts
The compression ratio inside the cylinder isn’t variable. The total cylinder pressure varies based on boost.
Right. Pushing more air means you have to add more fuel though to keep the mix right. The miles per gallon advantage there would have to be mechanical... More grunt at a lower RPM. As far as I can tell the 3.5 EcoBoost and 3.5 PFDI are both 10:1 engines, and both designed to run fine on 87. Maybe premium would offer a mileage advantage if you're pulling a heavy trailer or something?
 

·
Registered
nothing yet, but planning on an EV van
Joined
·
236 Posts
route might also affect things, going from east coast to colorado plateau will be an elevation gain of 5000-8000 feet
i notice this even on short trips, although, EVs are more sensitive because they are more efficient. i'm touch over a mile high and my friends house is at or slightly below 5000 feet. its 18 miles one-way but i use more power going home than getting there
 

·
Registered
Joined
·
1,022 Posts
The compression ratio inside the cylinder isn’t variable. The total cylinder pressure varies based on boost.
Right, the compression ratio when the piston is at top dead center cannot be changed. But if the ignition spark is not coming at top dead center, then the actual compression ratio of the fuel/air mixture at the moment of combustion will vary, depending upon when in the cycle the spark occurs.

This article confirms both a change in power and a change in mpg with a change in octane.

 

·
Registered
Joined
·
2,873 Posts
route might also affect things, going from east coast to colorado plateau will be an elevation gain of 5000-8000 feet
Right. And wind. And texture of the roadway, etc... things subtle enough not to notice. Which is why round-trip mileage is a better gauge of MPG than one-way. Always calculated by hand, to eliminate the computer error.
 

·
Registered
Joined
·
126 Posts
Right, the compression ratio when the piston is at top dead center cannot be changed. But if the ignition spark is not coming at top dead center, then the actual compression ratio of the fuel/air mixture at the moment of combustion will vary, depending upon when in the cycle the spark occurs.

This article confirms both a change in power and a change in mpg with a change in octane.

No doubt there's a change in power. Burning more fuel results in more power. It's true though they reported half a mile per gallon better, so ok then. Not enough difference to justify the use of premium, but apparently it's there, even to such a small degree. I stand corrected.
 

·
Registered
Joined
·
79 Posts
I recently drove my brand new 2022 148-EL HR AWD van from Kansas City to Seattle. Speed range was 55-70. Most of it being 60-65.

The worst mileage for a tankful was 16.5, in an absolute wind storm going through Iowa and South Dakota, which was mostly flat.

The best mileage was coming thru WA state, across the Cascades, at 19.5.

Average for the entire 2000 miles was about 18.
 

·
Registered
nothing yet, but planning on an EV van
Joined
·
236 Posts
Right. And wind. And texture of the roadway, etc... things subtle enough not to notice. Which is why round-trip mileage is a better gauge of MPG than one-way. Always calculated by hand, to eliminate the computer error.
for averages, yes round trip is the way to go, but i think the OP is looking for ways to explain why there would be a difference between to and fro
 

·
Registered
2019 250 148 mr
Joined
·
769 Posts
Variable valve timing can affect combustion pressures as well. Earlier valve opening and closing can raise effective compression, and increasing overlap can bleed off pressure during the compression stroke.

These motors are complex. The computer can change fuel mixture, ignition, boost, and valve timing several times a second. It's a complete system.
 

·
Registered
Joined
·
299 Posts
I have a 2017 T-250 ecoboost with a side ladder, roof deck, 4wd and a lift kit with larger tires. For longer (1000 miles+) trips, I get 16 +- 2 mpg. From my observations, if everything else remains the same, the MPG variance is due to the headwind/tailwind.

I'm at 50k miles now and the mileage has been pretty consistent. I usually drive 65mpg and gas grade doesn't seem to impact my mileage noticeably. At times when driving in MT, Nevada, Utah or Idaho where the speed limit is 80, I feel like I'm the slowest guy on the road:)

My wife is more aggressive as a driver and the mpg takes a hit as a result since that magnifies the air resistance.

FYI Since I forgot it, I looked it up on the Goog:
Air resistance can be calculated by taking air density times the drag coefficient times area all over two, and then multiply by velocity squared.
 

·
Registered
2022 W2X 350 HR AWD EB in Blue Jean Metallic
Joined
·
221 Posts
I just returned from a 3k mile trip. I left with 300 miles and returned with 3,300 miles. Most of the trip was at 70-85 miles an hour. I got just over 16mpg and always run premium fuel.
 
1 - 20 of 28 Posts
Top