Ford Fiesta MPG observation

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Rust_Belt_Pete

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I bought a brand new Ford Fiesta with the 6 speed "powershift" automatic transmission.
I usually take a trip to Rochester area from Buffalo one a week to see friends and inlaws and their "collection" of German shepereds and huskies.

I filled up with my local no name gas station with 91 octane ethanol free.
Drove to Rochester on the I90 the temperature outside was 56 degrees and I averaged the mileage back and forth from buffalo to rochester and back on the I90.
With minimal passing and cruise control on all the time I averaged 43.5 mpg on the highway.

Next week I filled my gas tank with NOCO 87 octane 10% ethanol, It was pretty darn cold and there was a bit of snow 37-42 degrees outside.
Same story same road same trip same amount of traffic and passing. 37.5MPG


Mileage was taken on the same strip of I-90 with about the same traffic.
Going to do another trip this weekend and see how my mileage is.
 
Can you fill up with some top tier Shell fuel? You may like it better than some of the other brands. I know I do.
 
No shell in Buffalo area near me that I know of.

I need to do more testing.
The owners manual says 87 and up, the compression ratio is 11:1.
That is a pretty high CR for 87 octane if you ask me, I think it might be more of octane function and not ethanol content.
Have to fill up with 10% 91 octane ethanol to find out.
Could it be the temperature that is a pretty big difference.
 
I would think the colder air would improve the mileage since the air is more dense and improves combustion. I wonder what 87 octane no-ethanol would do.
 
I watch the MPG display in my car all the time and would say the tests you have done mean nothing as they took place under difference circumstances. Lower temps, snow and possible wind make a big difference. In my experience, octane and ethanol would make 1 mpg difference at most.
 
I've noticed a large hit with 10% ethanol junk. I don't have a choice where I live, it is all 10% ethanol. But, on road trips I've come across pure gasoline and I notice a pretty good jump in mpg. I notices WAY less with just octance change than temperature. ALSO, you may got gotten summer blend fuel then winter blend fuel(it is that time of year, I believe). I've also noticed the biggest loss in mpg with the winter blend 10% ethanol that I get here in southern IL.

Originally Posted By: InhalingBullets
I would think the colder air would improve the mileage since the air is more dense and improves combustion. I wonder what 87 octane no-ethanol would do.


Dense air causes more wind resistance on the rest of the vehicle. Also, it takes everything else on the car longer to warm up and get to operating temperatures.
 
Originally Posted By: InhalingBullets
I would think the colder air would improve the mileage since the air is more dense and improves combustion. I wonder what 87 octane no-ethanol would do.


I dont know when the Fiesta runs in closed or open loop but generally cars a programmed to have a certain ratio of fuel to air. When the air is cold it is denser and more gets in the cylinder and requires more fuel to maintain the ratio. Plus there is the air density to push trough when the car is going down the road.
Dont know about the car but 37 degrees and 56 degrees makes a huge difference on a range with a rifle at 1000 yards.
 
Originally Posted By: InhalingBullets
I would think the colder air would improve the mileage since the air is more dense and improves combustion. I wonder what 87 octane no-ethanol would do.


Colder air decreases MPGs for several reasons. Combusion mixes get richer, wind resistance increases, fluid viscosities increase, tire PSIs decrease, etc.

The eco-modders will alter their intakes to warm the air before it enters the engine to get more MPGs as it leans out the A:F at the cost of HP.
 
Well that kinda explains why people on fiesta forums talked about getting better MPG after installing those [censored] cone filters that sit right next to the engine.
 
While I lived in OK used to drive to St. Louis, MO few times. Had the same powershift 6 speed ... got average 39.5 mpg on I-44. Tried most gas brands and different octane blends ... the difference was marginal.
 
Originally Posted By: J611
While I lived in OK used to drive to St. Louis, MO few times. Had the same powershift 6 speed ... got average 39.5 mpg on I-44. Tried most gas brands and different octane blends ... the difference was marginal.



There's no way a 6 MPG difference would occur by merely changing fuels.
 
I've got a 2013 Fiesta, same transmission. My MPG results in the Appalachian foothills has been around the 42-43MPG area. Great little cars, once you get used to the quirkiness of the DCT. Some people have complained of a oil leak near the Exhaust VVT solenoid, just a FYI. I've got a small seep there.
 
Ah neat, so to "smooth out" the curve so to say?

Thanks for the tip by the way. Is it on the timing belt side?
 
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You have to do some number crunching to see if the extra cost of higher octane fuel pays off on a per-mile basis.

So far with my Cruze, going to higher octane has not led to enough of an increase in mileage to overcome the extra cost per gallon.

I'll also agree that the OP needs to do more trips. There are too many variables to just compare the two trips and say the octane alone caused the difference. Surely, the octane caused some of the difference.
 
Yeah, it's on the timing belt side nearest you when you open the hood. Most people I've talked to have seen some minor leakage, nothing to get worked up over.
 
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