[Billfitz]

Since this zombie thread has been resurrected I might as well weigh in on this:

So let me get this straight- if you only refill when the number of remaining miles shown is less than 10, but never let the car totally run out of gas, is it really an issue ?

It is. There are dozens of sources on line that explain why. These are some of them: https://www.hsoil.com/reasons-to-keep-fuel-in-tank.html
https://www.savingadvice.com/article...-or-empty.html
https://mechanics.stackexchange.com/...east-half-full

[AdityaG]

I drove ~10 miles after “---“ and filled 17.4 gallons (15.8 fuel capacity)

[quakerroatmeal]

Originally Posted by AdityaG

I drove ~10 miles after “---“ and filled 17.4 gallons (15.8 fuel capacity)

Damn sounds like you like living life on the edge. Even took up the reserve tank anymore you'd be walking to the gas station lol

[thejeremyman9]

I didnt read through this whole thread since it seems like a necro bump, but you need to remember that the DTE mileage estimate is basically a rolling average fuel economy based on your recent driving. If you do a whole bunch of aggressive driving, then start driving gently (economically), then you can push far beyond the [original] DTE estimate. For example, I have driven aggressively for 10-15 miles, then gotten on the freeway and driven for 20 more miles (gently), and my DTE estimate is the same or higher after those 20 miles than it was 20 miles prior...

So lets say you have 1 gallons of gas left used in the DTE calculation. You averaged 10mpg recently because you were driving aggressively. DTE is 10 miles. You then get on the freeway with 1 gallon of gas and average 30 mpg. You can drive 30 miles, so 20 miles past the original estimate. Because its a rolling average, the DTE isnt going to immediately adjust based on your 30mph instantaneous fuel economy, so you can drive "past zero".

[Gen13 F36]

Who the F bump this thread

This is the kind of thing I don't want to find out. I never have my gas close to empty. I always fill up about 1/4 gas tank.

Do you know all the contaminant on your gas stay at the bottom of the tank?

[Jonwho2]

I hate to say it but all this "Its bad for a car to run low on gas" is BS in modern cars. Back in the old days when tanks were made out of metal and condensation could casue corrosion yes, it was a problem. But but modern BMWs. Believe or not engineers thought of people running low on gas and how that might affect the fuel pump. You're really worried of sucking up sediment under a 1/4 tank? lol what exactly do you think is floating at the bottom of you tank? I've never seen a BMW with a bunch of sediment in the tank. If you do, I suggest you keep the gas cap on.

[boosted14]

Dam I didn't even know our cars could get to zero on the fuel meter the lowest I have ever gotten is 48. I luckily have a station just 5 miles away from me that has E85

[Randy Johnson]

Originally Posted by sygazelle

Each time this question comes up I think of my first car, a 1961 Volkswagon.

One of its features is it did not have a gas gauge. Instead, it had a lever on the "firewall". When your engine started sputtering for lack of fuel, you simply reached down and turned this lever 90 degrees and magically you had an extra gallon or so of gas. Then, you started looking for a gas station. The good old days.

Now, however, the fuel pumps are in the tank and the gas actually cools the fuel pump. So, while you can take a chance and run it dry, you may not want to do it.

Hahaha what a blast from the past. I had an old honda 200 motorcycle that worked like this. Yes I could also just try to look inside the tank with a match or something....The switch worked better.

[Puzzo_in_the_6ix]

So I have the answer to the original question regarding how many km can you get after the range hits 0. The answer in my situation was 20km. I have a 2014 428i xdrive N20 motor. The car is 100 percent oem. I was driving home from work in rush hour traffic on hwy 401 when my range hit 0. I put it into eco pro mode and reset my trip count. In stop and go traffic I got 21 km before she quit.

[Abbeibne123]

Don't test this, there is dirt in the bottom of the tank and when your fuel level is low it can get in the injectors and damage them.

[eluded]

1.27 gallons left in fuel "capacity"

Car tracks 55L

[garyfried]

Originally Posted by sygazelle

Each time this question comes up I think of my first car, a 1961 Volkswagon.

One of its features is it did not have a gas gauge. Instead, it had a lever on the "firewall". When your engine started sputtering for lack of fuel, you simply reached down and turned this lever 90 degrees and magically you had an extra gallon or so of gas. Then, you started looking for a gas station. The good old days.

Now, however, the fuel pumps are in the tank and the gas actually cools the fuel pump. So, while you can take a chance and run it dry, you may not want to do it.

As I remember the old volkswagon I appreciate the story But I think firewall may be the wrong term being as the engine is in the rear. It was neat reaching down and swinging the lever for reserve.

[sygazelle]

Originally Posted by garyfried

As I remember the old volkswagon I appreciate the story But I think firewall may be the wrong term being as the engine is in the rear. It was neat reaching down and swinging the lever for reserve.

I had no idea the engine was in the back!

[CajunBMW]

Originally Posted by garyfried

As I remember the old volkswagon I appreciate the story But I think firewall may be the wrong term being as the engine is in the rear. It was neat reaching down and swinging the lever for reserve.

My first car was a 1971 super beetle. What a fun little car; with the engine in the back and the battery inside the car, it did great in the cold and snow. I had it at college and some of favorite moments were pulling into spots on campus that no other car could get into. If it was too small to parallel park, but still big enough for my bug, I would back in, and my friends and I would get out and would lift the front end up and get it into place. What fun memories.

[johnung]

Originally Posted by Puzzo_in_the_6ix

So I have the answer to the original question regarding how many km can you get after the range hits 0. The answer in my situation was 20km. I have a 2014 428i xdrive N20 motor. The car is 100 percent oem. I was driving home from work in rush hour traffic on hwy 401 when my range hit 0. I put it into eco pro mode and reset my trip count. In stop and go traffic I got 21 km before she quit.

The miles remaining estimate is a valuable tool because it does its job of getting you to a gas pump before the tank is empty.

Now that I'm running various concentrations of ethanol, I'm more concerned with how accurate the gas gauge itself is.

A 60 liter tank holds 15.85 gallons. But gas pumps shut off with varying sensitivity so they don't fill up completely. If I'm doing an ethanol calculation I will often use 15.6 gallons as the tank maximum.

I have a Zeitronix ethanol gauge on my dash so I always know exactly what the ethanol percentage was before I fill up and what it was after fill up. The gas station receipts tell me exactly how many gallons of E85 and/or 93 Octane were pumped into the tank.

Note: the federal govt allows gas pumps labeled "E85" to actually contain as little as E49. The station that I use has true E85 in summer and E75 in winter. The 93 Octane in my state (NJ) contains 10% ethanol by law.

I use my eye on the fuel gauge to see exactly which tick the fuel needle is on to be able to estimate what the % of the tank volume was at before I filled up. See photo.

Anyway the above provides a lot of data points for calculations. I also use the phone app called e85Cal to make things easier. I used to do it all by hand.

Probably the most interesting conclusion from my calculations is that when the eye shows the gas needle on the first tick, meaning that the tank is at empty, there is actually about 0.8 gallons of fuel remaining in the tank.

I've done this experiment many times. I run the tank down to that first tick, note the "before"ethanol % on my ethanol gauge, add measured amounts of E85 and/or 93 from the gas receipts, drive until the ethanol % stabilizes and note the "after" ethanol percentage.

Working backwards to solve for the "before" volume in gallons, it is never really zero as the eye on the gas gauge might have one believe. When the gauge needle first lands on that first tick, there's always about 0.8 gallons remaining in the tank. Fun math exercise! Good to know when searching for a gas pump.