400 mile tank - doable, but PITA

[paulca]

I managed 340 before chickening out and filling up. The total that day was 374 which I probably would have made on the tank without filling up, but didn't want to risk it.

400 would be tough, would need to be 95% highway / motorway.

[Dadhawk]

Originally Posted by paulca

I managed 340 before chickening out and filling up. The total that day was 374 which I probably would have made on the tank without filling up, but didn't want to risk it.

400 would be tough, would need to be 95% highway / motorway.

Not as tough as you might think, just nerve-racking but definitely not stop and go traffic.

Based on my usage, I look at 300 tank refills. Assuming that 13.2 US gallons is the usable fuel in the tank, I calculated the remaining miles to empty for each tank based on its MPG calculation.

Out of those, 186 would have been over 400 miles before empty, the max being 483 miles, most well over 400. The minimum was 383.

About 80% of these are from my standard commute (40.1 miles one way, usually takes me about 60 minutes, so avg about 40MPH but divided at about 80% at 55MPH and 20% at 0 to 35MPH).

[Tcoat]

Originally Posted by paulca

I managed 340 before chickening out and filling up. The total that day was 374 which I probably would have made on the tank without filling up, but didn't want to risk it.

400 would be tough, would need to be 95% highway / motorway.

I drive 682-720 miles a week. This is 98% highway with cruise set at 75MPH. I fill up once a week one week and then twice in the following week (just how the numbers work out I guess). I have never paid attention to how many miles I get out of a tank but would guess that I easily get 400 on a regular basis since I usually let the tank get almost empy. I will have to watch over the next few weeks and confirm or retract this statement.

[Tcoat]

Originally Posted by paulca

I managed 340 before chickening out and filling up. The total that day was 374 which I probably would have made on the tank without filling up, but didn't want to risk it.

400 would be tough, would need to be 95% highway / motorway.

I drive 682-720 miles a week. This is 98% highway with cruise set at 75MPH. I fill up once a week one week and then twice in the following week (just how the numbers work out I guess). I have never paid attention to how many miles I get out of a tank but would guess that I easily get 400 on a regular basis since I usually let the tank get almost empy. I will have to watch over the next few weeks and confirm or retract this statement.

[paulca]

I think I usually get between 250 and 280 a tank, but a lot (most) of my day-to-day mileage is stop and go traffic commuting.

On long road trips I regularly see 320 or higher. Usually those are starting after a tank with a few days commuting on it though.

On "usable" fuel. Does anyone know the amount of "tank" fuel the GT86 has? "Tank" fuel being fuel that cannot be pumped and is fuel for the tank itself effectively? (I take the term from aviation).

The 2017 has a "Miles to go" before empty and I determined it zeros out at around ~5 litres (1 UK gallon) remaining. However I doubt all of that could be pumped, so when it says zero... how far will it really go? Another 20? 30? miles?

[paulca]

Out of interest, over here, running out of fuel on the motorway is a traffic offense. You can actually be done for running out of fuel on the motorway as it's fairly dangerous for you to suddenly decelerate without brake lights. Fine on other roads, but the motorways have special laws.

[zoltiz]

Our consumption computer is a giant liar, btw. I record/reset every tank and math it, along with keeping track of the delta between actual and displayed MPG. My FR-S averaged 1MPG higher display than actual for 100-ish fill-ups, 86 so far is .8MPG higher on average, with some tanks being +1.8. I fill up at the same station 90% of the time.

Also, the more I baby the car, the more egregious the lie (my "35MPG" displayed results in 33.1 actual, while 25MPG displayed is 24.5-ish). Lies

[paulca]

Originally Posted by zoltiz

Our consumption computer is a giant liar, btw. I record/reset every tank and math it, along with keeping track of the delta between actual and displayed MPG. My FR-S averaged 1MPG higher display than actual for 100-ish fill-ups, 86 so far is .8MPG higher on average, with some tanks being +1.8. I fill up at the same station 90% of the time.

Also, the more I baby the car, the more egregious the lie (my "35MPG" displayed results in 33.1 actual, while 25MPG displayed is 24.5-ish). Lies

Check your speedo calibration. Often the MPG reads high because the speed and thus the distance reads high.

[zoltiz]

Originally Posted by paulca

Check your speedo calibration. Often the MPG reads high because the speed and thus the distance reads high.

Nah, speedo is fine, matches GPS value pretty well.

It's horrible at measuring amount of injected fuel when I'm in 6th gear going 30mph it seems.

[Tcoat]

Originally Posted by zoltiz

Our consumption computer is a giant liar, btw. I record/reset every tank and math it, along with keeping track of the delta between actual and displayed MPG. My FR-S averaged 1MPG higher display than actual for 100-ish fill-ups, 86 so far is .8MPG higher on average, with some tanks being +1.8. I fill up at the same station 90% of the time.

Also, the more I baby the car, the more egregious the lie (my "35MPG" displayed results in 33.1 actual, while 25MPG displayed is 24.5-ish). Lies

Don't think that a difference of less than 10% is a "massive" lie but yes the computer will not agree with what you calculate. It is taking a real time averages at all times where manual calculations do not account for such things as sitting in traffic for long periods.

[Dadhawk]

Originally Posted by Tcoat

Don't think that a difference of less than 10% is a "massive" lie but yes the computer will not agree with what you calculate. It is taking a real time averages at all times where manual calculations do not account for such things as sitting in traffic for long periods.

I think another contributing factor is the computer tops out on MPG at some point (don't remember what it is but I have noticed it). Basically, it will only give you "credit" for so much.

[Dadhawk]

Originally Posted by paulca

On "usable" fuel. Does anyone know the amount of "tank" fuel the GT86 has? "Tank" fuel being fuel that cannot be pumped and is fuel for the tank itself effectively? (I take the term from aviation).

That's a tough one. From what I've read in the past most (but not all) auto manufacturers list it based on useable fuel but it is an average calculation and can vary by as much as 3% between cars of the same model due to manufacturing "sloppiness" in the tank. Probably more common in metal tanks than non-metal ones.

[Decep]

Originally Posted by Dadhawk

I think another contributing factor is the computer tops out on MPG at some point (don't remember what it is but I have noticed it). Basically, it will only give you "credit" for so much.

true, 127mpg coasting. this would probably be why

[paulca]

Originally Posted by Decep

true, 127mpg coasting. this would probably be why

Yep. But it hides the difference in efficiencies between engine braking in 6th with 0 fuel flow and coasting clutch down (or neutral) which consumes "idle" fuel.

To eco-mile, if you need to slow anyway use engine braking in the gear that will get you that deceleration. If you are trying to sustain speed, use neutral.

If you free wheel in neutral to a stop the 127mpg starts to decrease and register around 20mph.

The real test of fuel efficient driving in my book is not how far you can go on a tank, but how high you can get the MPG in rush hour traffic. Takes an awful lot of concentration to get it above 40mpg. (UK gallons) (33.307MPG US gallons)

This morning I eco-miled to work and back. When I left the house the miles to go said 24. It's 12 miles each way to work. When I got home it read 7 to go. Average for the tank was 30mpg. So I significantly exceeded that today, seeing 45MPG (37.5 US MPG) for a while on the way to work, till I hit traffic.