[natahoa]

I’ve been filling with 93 octane, because no gas stations have 91. Today I went to our local/rural service station and decided to fill up (half tank) with no ethanol gas, which is 89 octane.

My fuel monitor has gone crazy. I started with the usual 550+ miles, drove maybe 10 miles, and it is now down to nearly 450 miles remaining in the tank.

I thought I’d get better mileage with no-ethanol. Does anyone know what is happening - in not-too-technical terms?

[AndroidRobot]

there are too many variables here to make a fair assessment. if you're not running the proper octane your engine will retard the spark to prevent pre ignition even running non-ethanol fuel

[sk0rchi]

You are reacting too early and have driven too few miles to see the benefit.

I have deduced that the range indicator works in real time based on most recent efficiency (initially would have thought it would have used data stored in the "individual" trip bucket). Driving 10 miles is a small data sample for the computer to make a projection, albeit it is likely accurate given those 10 miles.

It will take time to see benefit from using different fuel. Tanks with mixed fuels will complicate matters as the ECU has to adapt to new parameters. Several tanks later, the ECU will have settled, assuming no change in fuel and you can then determine which fuel is better for your driving habits.

Keep in mind also, that yours is still very new and things will continue to improve post break-in.

[roadkillrob]

ethanol also has higher octane which lets you run more spark advance etc - which gives more power efficiency etc and the engine is built to run on high octane, so it compensates for low octane and certainly does not run as optimally. I am guessing the distance to empty over reacted and will settle out at something in between though.

[natahoa]

Originally Posted by sk0rchi

You are reacting too early and have driven too few miles to see the benefit.

I have deduced that the range indicator works in real time based on most recent efficiency (initially would have thought it would have used data stored in the "individual" trip bucket). Driving 10 miles is a small data sample for the computer to make a projection, albeit it is likely accurate given those 10 miles.

It will take time to see benefit from using different fuel. Tanks with mixed fuels will complicate matters as the ECU has to adapt to new parameters. Several tanks later, the ECU will have settled, assuming no change in fuel and you can then determine which fuel is better for your driving habits.

Keep in mind also, that yours is still very new and things will continue to improve post break-in.

Thanks so much! I’ve been filling when half full, but I’ll probably let this tank empty before I fill again.

Do you have any idea why the fuel gauge is acting so wonky? I have zero expertise in this, but would like to learn anything I should know for this car.

This local station doesn’t have premium gas, only 87 and no-ethanol. I don’t plan to use it all of the time, but it will be interesting to see how the fuel gauge reacts with this gas.

[sk0rchi]

Originally Posted by natahoa

Thanks so much! I’ve been filling when half full, but I’ll probably let this tank empty before I fill again.

Do you have any idea why the fuel gauge is acting so wonky? I have zero expertise in this, but would like to learn anything I should know for this car.

This local station doesn’t have premium gas, only 87 and no-ethanol. I don’t plan to use it all of the time, but it will be interesting to see how the fuel gauge reacts with this gas.

I love the word 'wonky' - one of my favorite non-word words.

Anyway, as I said; it is my belief that indicated range is based on data that is very recent. What I do not know is what that program is.

For the sake of illustration, lets use this as an example:

Lets say the indicated range is based on average fuel economy over the last 50 miles (again just for this example, this is unknown)

If your fuel economy was 20mpg over that 50 miles, then the range is the math of fuel remaining x that efficiency (20mpg * 22gal = 440 which close to the range you mentioned in the OP).

If you go drive 30 miles on the freeway, you'll see it improve right away - I've driven 90 mile trips where I only lost 5 miles of range from when I started.

[Marty in NY]

Originally Posted by natahoa

I’ve been filling with 93 octane, because no gas stations have 91. Today I went to our local/rural service station and decided to fill up (half tank) with no ethanol gas, which is 89 octane.

My fuel monitor has gone crazy. I started with the usual 550+ miles, drove maybe 10 miles, and it is now down to nearly 450 miles remaining in the tank.

I thought I’d get better mileage with no-ethanol. Does anyone know what is happening - in not-too-technical terms?

I believe its pretty much like others have said and I couldn't find any sort of algorithm in the manual but I do know on my GTi, the "miles to go before empty" is based on.. ..
- Amount of fuel in the tank
- Historical driving style within the last "X" miles (pedal to the metal or eco foot)
- Current driving style (who's nagging me from the back seat)
- Which mode I'm in (eco, sport, etc)
- Grade of road (uphill, downhill, flat)
- Am I using the auto tranny or do I have it in steptronic mode
- How sensitive the algorithm is and the accuracy of components in the circuit

Maybe there's more to it but those are enough variables to cause a change in the miles-to-go number minute by minute. I also think the fuel level indicator comes in its own varieties. The fuel level in the Golf diesel we had was not linear at all. It would take close to 100 miles before it moved off of full but when it was below a quarter tank, it dropped like a lead balloon. Heck, for every 1.5 miles I drove, it would drop 5.
So, just keep an eye on yours and you will get an idea over time of how it works.

[natahoa]

Thanks all!

This is the third half tank of gas I’ve added. The previous two times it was very consistent. The huge change kinda blew my mind. I’m not worried - just checking to see if I should be concerned.

[Marty in NY]

Originally Posted by natahoa

Thanks all!

This is the third half tank of gas I’ve added. The previous two times it was very consistent. The huge change kinda blew my mind. I’m not worried - just checking to see if I should be concerned.

Normally I would just say to keep en eye on it in order to get used to how it behaves but due to all the reported issues on the G05, you will also want to keep an eye on it in case its flaky or decides to fail. You don't want to run out of gas.
I had my oil and fluids changed at a BMW dealer a couple years ago. When the car was ready, I paid and took off and about three or four miles down the road I decided to check the oil level via iDrive. It takes a few miles of driving before it registers. When I checked, it registered a quart or two down from max. I thought, how can this be, I just had it changed, it never indicates less than max??? So I turned around, went back to the dealer and showed them. They shrugged their shoulders and said they would put it back in the shop. I said, hold on, you just released it, didn't you check the level that iDrive was reporting? They said they never do, they drain and fill with the correct amount and that's it.
Turned out my oil level sensor decided to cough up a furball, they replaced it and its been fine since. Ya just gotta know your car and keep an eye on things because only you know its personality/character.

[AndroidRobot]

Originally Posted by natahoa

Thanks so much! I've been filling when half full, but I'll probably let this tank empty before I fill again.

Do you have any idea why the fuel gauge is acting so wonky? I have zero expertise in this, but would like to learn anything I should know for this car.

This local station doesn't have premium gas, only 87 and no-ethanol. I don't plan to use it all of the time, but it will be interesting to see how the fuel gauge reacts with this gas.

ethanol has a higher octane rating but lower energy density (usually about 108octane) This means tou can compress it more without detonating and overcome that threshold. You will get worse mileage but make more power on E85 with a properly high compression ratio than off 95 octane ethanol free fuel. It's a complicated subject, I suggest you do some research on it.