[JChristie]

Just thought I’d share the results of my little driving experiment today. I will start by saying that I fully realise running a tank near empty is a stupid thing to do, but take this opportunity to learn from my idiocy.

I was driving around town in an area with lots of gas stations. My low fuel warning light had come on and I was curious how accurate the fuel range was and continued driving for a bit. I pulled into a gas station with my car estimating I could only go another 1 kilometer before running dry. My average MPG at the time was 21.5 (I say this as the range estimate varies depending on your current fuel economy). It took 48.5 litres of gas (12.8 US gallons) to fill the 52 litre tank (13.7 gallon tank). So there was less than a gallon of fuel left in the tank if the published specs are accurate.

TLDR – Fuel gauge/range is pretty darn accurate, if it says you’re on empty you probably are.

[BPC]

thanks. what is a kilometer? heh.

[B.a.f]

Originally Posted by BPC

thanks. what is a kilometer? heh.

1 km = 1000 meters

[NVHoo]

Originally Posted by JChristie

Just thought I’d share the results of my little driving experiment today. I will start by saying that I fully realise running a tank near empty is a stupid thing to do, but take this opportunity to learn from my idiocy.

I was driving around town in an area with lots of gas stations. My low fuel warning light had come on and I was curious how accurate the fuel range was and continued driving for a bit. I pulled into a gas station with my car estimating I could only go another 1 kilometer before running dry. My average MPG at the time was 21.5 (I say this as the range estimate varies depending on your current fuel economy). It took 48.5 litres of gas (12.8 US gallons) to fill the 52 litre tank (13.7 gallon tank). So there was less than a gallon of fuel left in the tank if the published specs are accurate.

TLDR – Fuel gauge/range is pretty darn accurate, if it says you’re on empty you probably are.

Personally, I prefer being warned earlier. My past experience with Audi and Mercedes indicated the light came on once the tank had less than 2 gallons. I doubt that the fuel system in the 2 is efficient enough to suck out the last drops of fuel, so alerting you with less than 1 gallon left is pretty dire. Maybe if you are always in an urban area with a gas station on every corner then that is OK, but in the rural mid-west and west you can easily be 10 miles or more from a gas station. Yeah it would be pretty stupid to let it get that low in the first place, but what good is an alert if it leaves you little margin to do anything about it? The "miles to empty" on the Mercedes was also pretty accurate, like the 2. The MTE on my TT is pretty worthless it varies so much when near empty.

[moldcad]

I'm sure BMW incorporated some 'idiocy factor' into the warning system, and you would continue for quite a distance even after it says zero. Or maybe not? BMW have started showing some symptoms of idiocy themselves lately

That said, I always fill mine up when the needle is around 1/4 of the tank, simply because with so many kilometers of virgin new motorways in Poland with gas station only catching up, a medium distance between them (particularly on those just finished stretches of new roads( can be as high as 70-80 km... With my driving style (180-200 km/h on a motorway is a norm; I consider myself extremely lucky with no speeding tickets since buying the M235i, and just one but earned with my R)...

[JChristie]

Originally Posted by NVHoo

Personally, I prefer being warned earlier. My past experience with Audi and Mercedes indicated the light came on once the tank had less than 2 gallons.

Sorry, to clarify, the car starts warning you about your fuel state much earlier. The first warning comes when you're at about the 1/4 tank level and then the car starts nagging you when your range hits 30 miles/50 km. I just stupidly kept driving in spite of the warning and gassed it up on empty.

[voukephalas]

I've wondered this myself and would much prefer a 99% accurate "miles to empty" indicator than early warning. The gauge is perfectly legible so a warning when a quarter tank of gas is left is just an annoyance.

I haven't pushed it on this car but have driven 25 miles in my other car when the indicated range was "0 miles". I've driven down to just barely zero range in the BMW and still didn't quite reach 13 gallons when refueling.

What are the potential issues of driving on empty besides getting stranded? Is there any mechanical issue (fuel pump, etc.?).

[Nahlem]

Mine Aint accurate it warned me 90 km to empty tank, fueled it up it only took 40 liters from a 52 liter tank .

[Zooks527]

Originally Posted by Alden_88M

Mine Aint accurate it warned me 90 km to empty tank, fueled it up it only took 40 liters from a 52 liter tank .

Which is effectively what the first poster showed. You got the warning that there was 50 - 60 miles (~2 gallons) left on your tank, and it took 3 fgallons less than a full tank.

So, it would have shown 0 miles to go with about a gallon left in the tank, just like the OP.

Now, mind you, I find that stunningly inaccurate, as opposed to what I think the general tenor of the thread to this point has been. Telling my I'm dry with a gallon left isn't doing me any favors.

[VIDoug]

Originally Posted by JChristie

Sorry, to clarify, the car starts warning you about your fuel state much earlier. The first warning comes when you're at about the 1/4 tank level and then the car starts nagging you when your range hits 30 miles/50 km. I just stupidly kept driving in spite of the warning and gassed it up on empty.

I tested this recently -- my warning was at 75 km

[allthatisntnow]

Originally Posted by voukephalas

I've wondered this myself and would much prefer a 99% accurate "miles to empty" indicator than early warning. The gauge is perfectly legible so a warning when a quarter tank of gas is left is just an annoyance.

I haven't pushed it on this car but have driven 25 miles in my other car when the indicated range was "0 miles". I've driven down to just barely zero range in the BMW and still didn't quite reach 13 gallons when refueling.

What are the potential issues of driving on empty besides getting stranded? Is there any mechanical issue (fuel pump, etc.?).

Yeah, reduced cooling for the fuel pump that needs to be immersed and potential sediment uptake from the debris that collects at the bottom of the tank over the years.

[moldcad]

Originally Posted by Zooks527

Now, mind you, I find that stunningly inaccurate, as opposed to what I think the general tenor of the thread to this point has been. Telling my I'm dry with a gallon left isn't doing me any favors.

I agree in 100% - making the driver worry about his fuel being low too early is just yet another factor making driving under stress, which is never a good thing (it spoils the pleasure we're getting from driving those otherwise great machines, but above all it can distract us from any possible, much more important factors - thus negatively influencing the safety).

[Nahlem]

I think it should warn me when i have 5 liters left thats a LOT When you switch to comfort mode or eco mode thats more then enough for me to get to a gas station. Even When its run out out of fuel it will still go on on the gas fuemes that are left but after that your Done for it. :-D

[2msport]

There's around 1.5-2 gallons left when you are on empty (0 miles left). That's pretty idiot proof right there.

[Nahlem]

I think you misunderstood me, i think its annoying when its warning me to early the tank is 52 liters the meter says 95 km to empty tank so when going to the gas station to fuel up it only fills up 40 liters that means I have 12 liters left so it's warning me too early. Wish it would do that when it's 5 liters left. That would be perfect.

[BoomWasabi]

Originally Posted by JChristie

I pulled into a gas station with my car estimating I could only go another 1 kilometer before running dry. My average MPG at the time was 21.5 (I say this as the range estimate varies depending on your current fuel economy). It took 48.5 litres of gas (12.8 US gallons) to fill the 52 litre tank (13.7 gallon tank). So there was less than a gallon of fuel left in the tank if the published specs are accurate.

You can also use Connected app (otherwise useless). it gives a good estimate of how much fuel is left in the tank. Try it just before filling up your car.

[BoomWasabi]

Originally Posted by 2msport

There's around 1.5-2 gallons left when you are on empty (0 miles left). That's pretty idiot proof right there.

I wouldn't count on this at all.

[2msport]

Originally Posted by BoomWasabi

I wouldn't count on this at all.

You know just about every car has this similar volume as a buffer.

[sputman]

I've coded my car so it only shows low fuel once it reaches 50km. I've also ran my car to zero km left and could fit 50l of gas, yielding a buffer of 2-3 liters, or 20 or so km.

I think the furthest I've gone past this test is 10km and was fine.

[overcoil]

So does the car use the level sensor plus an average of past fuel usage rate to display a 'miles remaining' # on the dash?

[JChristie]

Originally Posted by ScottSinger

So does the car use the level sensor plus an average of past fuel usage rate to display a 'miles remaining' # on the dash?

According to the manual the range is calculated based on your average MPG over the past 20 miles (30 km). Not sure how accurate the fuel level reading is.

[BoomWasabi]

Originally Posted by 2msport

You know just about every car has this similar volume as a buffer.

Most car have some reserve. But counting on extra 2 gallons might get you in trouble.