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2017 T350HD HR EL 3.5EB 3.73 Cargo, Tinted, Alcoas
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Discussion Starter · #1 ·
Hello Transitonians!
I have driven my 2017 350HD HR EL Ecoboost 3.73 for about 5 months now. I am very impressed with the performance and drivability of my van.

Current mileage is 48,353. Most of my daily driving is 65% city 35% hwy and I have been averaging 16 to 18mpg all summer and one time on a hwy trip I actually averaged 20 mpg!

Here in Michigan the weather has been trending colder and coincidently my mileage per gallon has been really dropping! Lately I am dipping into the 13's and 14's for mpg.

I did just install a K&N Airfilter and recently in the last couple days since the filter swap I am back up to the 16's for mpg. I must be very careful not to take off too aggressively and also to try to coast longer for exits and stop lights in order to achieve and "good mpg numbers at all. If I drive it like a car in traffic the mileage is doomed.

I rarely will ever pull a trailer and am unlikely to haul much weight ever.

Let's assume my motor is fine. Let's also assume my poor mileage is directly related to my 3.73 rear end gear ratio. Big question: Since I do not haul heavy, would it be prudent for me, in theory, to swap my rear end gears for the taller gears? Has anybody done this? Will I have to change anything else in the van including reprogramming/changing the ecu, etc?

Any feedback is appreciated especially if you have experience with any of the miles per gallon issues I am illustrating. Cost for the swap would be another factor to consider.
If the rear end swap will save fuel there will be a point at which the swap will potentially pay for itself I assume. Therefore it should be done sooner the better.

Also, I just swapped my aluminum wheels with 205 Hankooks for my stock steelies shod with 205 Michelin Agilis Cross Climates. The Michelins and superior in weather and much softer and thus smoother and quieter!
 

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Most of us with early model ecoboost transit's have economy gearing of of 3.31. I average 16.7 mpg for mostly highway, I was always pleased with that. That 8 cylinder GM product I was driving before I got the transit averaged 8 mpg.
 

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U8U 350 HD Ext. DRW HR
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I have the same van 2021 with drws and awd. I get 13 to 14 around town and around 17 on highway per gas meter on van. I reset gas meter on long highway trip to see what each is though. Also in town I turn off auto off button.
 

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Winter gas mileage always drops. Winter gas is Blended different and makes it drop the mileage drop also. If it was me I would put the stock air filter back on.
Yes, K&N seem to be kryptonite for turbochargers. Great for an old carbureted vintage car, but all kinds of tales of woe for modern vehicles. I'm not speaking from experience; just repeating what I've read on this and other forums.

I take it Winter Blend has more ethanol? I never looked it up.

My engine hours are about 80/20 city/highway, and my avg for 114k miles is 15.3.
 
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Yup. What Bill says. The K&N is nothing but trouble for a turbo.

1) problem is the oil quickly contaminates the MAF, which causes the A/F ratio to lean out. Short term you may feel a slight improvement in responsiveness and maybe even fuel economy, but eventually it'll lean out to the point that detonation can happen. Mild detonation will result in more fuel use, at it enriches the A/F ratio to combat that. But if it's severe enough, you'll just start burning up your valves or just blow out the head gaskets.

2) Oiled air filters cause a condition called "dust-out", where silica erodes the turbo vanes or even cause cylinder wall scoring. It became such a problem on the Cummins 5.9 and 6.7L that Chrysler issued a "Dust-Out" diagnosis guide so that they wouldn't keep eating those warranty costs.

http://www.engineprofessional.com/TB/TB012615-1.pdf and https://testing-public.carmd.com/Tsb/Download/82072/080022dc8201ed28

Anyways.... back to the original problem... The EcoBoost (or any direct injection turbo motor) will NOT get fuel economy in short-cycle driving, where it's doing frequent cold starts, because of fuel enrichment. Is is possible, you trips have become shorter, or you it's cooling down more between trip?

If you're sure all of your driving conditions are the same, the first place to always start is basic Preventative Maintenance. Meaning new spark plugs and a new OEM equivalent filter (Motorcraft, Napa Gold, Wix, Purolator Pure-One etc). Trying to change anything else before the basics is just introducing confounding variables.

The 3.73 rear axle ratio probably accounts for about 1 MPG on the highway. It likely doesn't have any affect in-town.

If you want to go down the tuning route, 5-Star tuning can provide an Economy tune, which is similar to Eco Mode in the 2020+ transits, in that throttle response is re-mapped to keep it out of Boost under most conditions. You could also add a boost gauge. My Focus has one, and we added a digital one to our Fiesta EcoBoost. Being able to see when you're getting into boost definitely can aid fuel-saving driving.
 

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2018 T350HD Dual Sliders - SOLD
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Cost for the swap would be another factor to consider.
If the rear end swap will save fuel there will be a point at which the swap will potentially pay for itself I assume.
Back in 2018 a friend swapped out the 3.73 for a 3.31 since he was almost always highway driving and was looking for better mileage. The gear set was $185 back then. I can't imagine it has gone up that much since.
 

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Winter gas mileage always drops. Winter gas is Blended different and makes it drop the mileage drop also. If it was me I would put the stock air filter back on.
agreed, and typically you end up idling more waiting for vehicle to warm up, and windshield to defrost. Plus cold air is more dense and takes more fuel to push a vehicle through. I've always noticed reduced mileage in cold months.
 

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agreed, and typically you end up idling more waiting for vehicle to warm up, and windshield to defrost. Plus cold air is more dense and takes more fuel to push a vehicle through. I've always noticed reduced mileage in cold months.
The winter blend has more lighter fractions that vaporize easier and contain less btu.
 

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2017 T350HD HR EL 3.5EB 3.73 Cargo, Tinted, Alcoas
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Discussion Starter · #11 ·
Back in 2018 a friend swapped out the 3.73 for a 3.31 since he was almost always highway driving and was looking for better mileage. The gear set was $185 back then. I can't imagine it has gone up that much since.
Thanks! I wonder what his long term evaluation is regarding drivability and economy? "Is he happy enough with the rear end swap; would he do it again or would he recommend it to others?"
 

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Discussion Starter · #12 ·
Yes, K&N seem to be kryptonite for turbochargers. Great for an old carbureted vintage car, but all kinds of tales of woe for modern vehicles. I'm not speaking from experience; just repeating what I've read on this and other forums.

I take it Winter Blend has more ethanol? I never looked it up.

My engine hours are about 80/20 city/highway, and my avg for 114k miles is 15.3.
"Great!" The K&N was $78! Hate to toss it!
 

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Thanks! I wonder what his long term evaluation is regarding drivability and economy? "Is he happy enough with the rear end swap; would he do it again or would he recommend it to others?"
He was on the fence about it. Mileage was a slight improvement but it was shifting through the gears a lot more. Mind you this was back when the Transit was a 6 speed.
 

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"Great!" The K&N was $78! Hate to toss it!
If it lets more air in without a larger intake, it's doing that only by filtering less. There is no magic. I was in the motorcycle industry for 18 years and I lost count as to how many times we would find dirt on the AFTER side of an air filter. I'll never run one in a vehicle I own.
 

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1) problem is the oil quickly contaminates the MAF, which causes the A/F ratio to lean out. Short term you may feel a slight improvement in responsiveness and maybe even fuel economy, but eventually it'll lean out to the point that detonation can happen. Mild detonation will result in more fuel use, at it enriches the A/F ratio to combat that. But if it's severe enough, you'll just start burning up your valves or just blow out the head gaskets.
Ha! 20-some years ago, when I was driving a 1.8T turbo VW GTi, everyone on the forums loved K&N's. Then there were the endless threads about cleaning MAFs. :rolleyes:
 
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