MPG + Maintenance Questions

[TorqueMan]

Very interesting stuff. I find it hard to bring my average mpg's over 24 while driving economically. For you manual guys out here, how do you drive to get decent mpg's? Do you completely stay out of boost and take the car to 3k rpm to keep up with traffic? Or do you go into a little boost and shift earlier? I am just trying to find the sweet spot for efficiency.

There is a case to made for both sides of the argument. One side says stay out of boost, and therefore use less gas to accelerate. The other side says mild boost allows for quicker acceleration, and therefore you spend less time under acceleration which will ultimately mean using less gas. I'm a believer in the second approach, as long as you don't go crazy with the boost. The torque curve for our engines is mostly flat between 2500 and 5500, so if you accelerate using light boost while keeping the RPMs between 2500 and 3000 you get acceptable performance for most daily driving situations. Plus, I don't find it particularly safe to merge onto a 70 mph Interstate at anything below the speed limit, which is nigh impossible without using boost.

My driving is 80/20 highway/city driving. Using this strategy, while limiting the number of cold starts, and keeping under 75 mph on the highway, I average 28-29 mpg. I have been forced on occasion to go long distances between 60-65 mph. On those tanks my average mpg goes over 30. This is with just me in the car with negligible winds. All of my mpg measurements are taken manually. The computer estimates average 1.5 mpg over measured.

Based on my experience, I believe my car averages pretty close to EPA estimates for a stock engine, manual tranny with 3.31 gears.

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[BlueBoost]

There is a case to made for both sides of the argument. One side says stay out of boost, and therefore use less gas to accelerate. The other side says mild boost allows for quicker acceleration, and therefore you spend less time under acceleration which will ultimately mean using less gas. I'm a believer in the second approach, as long as you don't go crazy with the boost. The torque curve for our engines is mostly flat between 2500 and 5500, so if you accelerate using light boost while keeping the RPMs between 2500 and 3000 you get acceptable performance for most daily driving situations. Plus, I don't find it particularly safe to merge onto a 70 mph Interstate at anything below the speed limit, which is nigh impossible without using boost.

My driving is 80/20 highway/city driving. Using this strategy, while limiting the number of cold starts, and keeping under 75 mph on the highway, I average 28-29 mpg. I have been forced on occasion to go long distances between 60-65 mph. On those tanks my average mpg goes over 30. This is with just me in the car with negligible winds. All of my mpg measurements are taken manually. The computer estimates average 1.5 mpg over measured.

Based on my experience, I believe my car averages pretty close to EPA estimates for a stock engine, manual tranny with 3.31 gears.

Makes sense. I wonder if going into boost constantly or staying out of it mostly has any impact on engine life in the long run. 29 mpg is pretty good for highway and city driving. I was only able to obtain similar numbers on a long road trip. I'm also curious to know if you could tune the car to start going into boost only at higher rpm's. Probably doesn't work that way I imagine.

 

[TicTocTach]

Return trip complete. Gas station right next to the hotel, but had 8-10 miles of stop-n-go traffic getting out of San Antonio. Highway 281 is a good old rural 2-lane road for most of its length, with a bunch of small towns along the way. Speed limit is mostly 70, but some counties have it at 75. Through those areas I bumped the speed up to 73, but there was enough traffic that I was never holding anyone back. Was only able to use cruise control about half the time. About the same headwinds nearly directly out of the south, so they were tailwinds this time. Ambient temps started in the mid-90's, peaking around 100 when I got home. Load in the car is identical to the trip down.

20180825_70mph-profile by clair_davis, on Flickr

I filled up as soon as I got home, 10.172 gallons over 289.4 miles, for 28.45mpg actual, 30.8mpg indicated. Almost the same indicated mpg as my previous (not this trip) 80mph adventure, but the error is less for whatever reason. I'm pretty happy with a solid 28mpg over this route, and it's pretty clear that the EBPP is sensitive to speed if you're looking for mileage. There probably won't be an opportunity for me to drive slower than that for any extended period, so I'll keep seeing what I can do to improve mileage at or around 70mph going forward.

Clair

 

[TorqueMan]

I filled up as soon as I got home, 10.172 gallons over 289.4 miles, for 28.45mpg actual, 30.8mpg indicated. Almost the same indicated mpg as my previous (not this trip) 80mph adventure, but the error is less for whatever reason. I'm pretty happy with a solid 28mpg over this route, and it's pretty clear that the EBPP is sensitive to speed if you're looking for mileage. There probably won't be an opportunity for me to drive slower than that for any extended period, so I'll keep seeing what I can do to improve mileage at or around 70mph going forward.

Keep in mind that measuring mileage from a single tank will introduce errors. There are various factors (flow rate, sensitivity of vapor return valve in the pump handle, etc.) that affect when the pump clicks off, so each fill up may have more or less fuel in the tank. This is assuming you don't top off, which you absolutely should NOT do. The very best way to compute mileage is to measure over at least three tankfulls to average out the differences in fillup total.

That said, your measurements appear to confirm the EPA estimates (IIRC, 29 mpg) for a performance pack-equipped 2018 EcoBoost. A 10-20 mph tailwind averages out to 15 mph. Subtract that from 70 and you get 55, which is the speed EPA tests are designed to test at.

Thanks for taking the time and effort to collect this data--it was very informative. I may have occasion to take a very long trip indeed (2000+ miles) in the next few weeks. If that happens I'll collect similar data and share.

 

[TicTocTach]

Keep in mind that measuring mileage from a single tank will introduce errors. There are various factors (flow rate, sensitivity of vapor return valve in the pump handle, etc.) that affect when the pump clicks off, so each fill up may have more or less fuel in the tank. This is assuming you don't top off, which you absolutely should NOT do. The very best way to compute mileage is to measure over at least three tankfulls to average out the differences in fillup total.
...

I assume that there must be some way to calibrate the mileage calculator function, but I haven't dug into that capability yet. In my previous DD, I had installed a ScanGauge II that I think used injector duty cycle & MAP sensor data to calculate fuel used. From that number, there was a quick trim adjustment that could be entered into the unit to calculate fuel used to within a couple tenths of a percent tank to tank.

I always let the pump run on the wide open setting until I'm within a a couple gallons of full, then manually fill at about half speed until the pump shuts off automatically. No topping off, but consistent process each time. Hard part for me at this point is estimating where I need to slow down the pump - previous DD had 10-gallon tank and the ScanGauge was spot on. I also haven't wrapped my mind around a 15.5 gallon tank yet...

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