I have an app on my iPod called Dash Command, I think it came with my bluetooth OBDII reader (GoPoint BT-1).

The fuel level is shown in percentage. When it's on the fuel reserve, it says it's below 15%, I recently saw it at 8%,

When I fill up (I usually just stop when the pump clicks off) it only shows about 60%, even though all the LEDs on the fuel guage are lit up.

So is there really another 40% more room in the tank? Would that number go up much quicker if I put more gas in? Is it about the shape of the tank or where the float is, there's 40% more height to the top, but there's really just a tiny bit more space?

If you have an OBDII reader, what does it read when you've trickled as much gas in as you dare?

 

Can't speak to the percentage shown by the app, but if you top off your gas tank (meaning adding more after the pump clicks off), there are lots of MINI owners who ended up with damaged fuel tank breather valves and/or charcoal canister issues, one or both in turn leading to difficulties getting fuel into the tank (pump keeps clicking off) and subsequent repair to fix the refuel issue.

So I wouldn't recommend trying to get more into the tank, on that alone.

Probably more useful than a percentage report would be absolute quantity of fuel (gallons, whatever) in the tank when full. That can be compared to known quantities for tank capacity and discussed to death in the forums

 

I will have to try to see how well the percentage lines up with what I put in the tank. I will need to keep track of the temperature and fuel level over a couple of refills. It looks like the effects of temperature will be negligible.

Yes, I can see why the capacity was discussed to death. On the 1.5L 3 cylinder, there are several numbers out there, 40L, 44L or 50L, and then you throw in two kinds of gallons and you get a big mess.

Is there any consensus? My 3-cylinder car is from August 2014, made for Canada. Everything I have from that time (PDF manual, spec sheet) suggests 40L. The PDF manual is a bit confusing.



The physical manual only has one number, 44L, so that's probably correct for Canada at that time,

 

It looks like the PID Fuel Tank Level is one of the basic ones that all cars send out, and they all send it out as a percentage. In airplanes you never trust the guage, you use a stick.

 

That slice of the PDF has got to be one of the wackiest bits of confusion I have ever seen. Wow.

Using Bimmerlink on my 2017 Cooper S, I can actually get a reading for number of gallons in the tank. Based on the PID being a generic thing, I would conclude what Bimmerlink is showing is BMW-proprietary (and presumably what the rest of the car is actually using to figure stuff out). Might be worth a look. You may not even need to use the paid/licensed version of the app to get the stat (though it has been so long since I updated to the paid version that I don't recall).

 

I have the first set of data points.

The temperature, which shouldn't matter much, was -10'C (14'F). The Fuel Reserve message had just come on about 3 miles earlier, it was on one bar. The Fuel Tank Level was 9.3% before refueling. I will have to pull over the moment I get the Fuel Reserve message next time, I'll bet it is right at 10%. I stopped when the pump clicked. I put in 38.55L (FYI about $60 Canadian, $45 U.S. or approx. $4.50/U.S. gallon). The Fuel Tank Level was 71.4% after refueling.

If 38.55L were 62.1% of the tank then it would hold about 60L. Assuming the reading 71.4% is 44L, 9.3% of 44L is about 4L, but I'm guessing there was really 5.5L left in the tank at the start. Oh, but 100/71.4*4L is 5.6L, so that's a pretty good match.

It would usually be a few weeks before I would fill up again. I think I will try filling up from half-a-tank. I wonder if I can be brave enough to put in an extra litre. Not next time, but maybe the time after next.

Oh, one more thing, when I was parked in my parking spot at work, the fuel tank level was 72.2%, then it was back at 71.4% when I put the car on level ground.

 

I filled up from 5 bars, 38.0%. It stopped again at 71.4%. I put in 16.45L, so I guess the guage is not linear! 71.4/44*38=23.5, so it would have taken 20.5L to fill up if it was linear.

It will be a few more weeks.

So far I'm guessing:

71.4% = 44L
38.0% = 27.5L
9.3% = 5.5L

It would be great if I could find a lonely pump somewhere I could put in a litre at a time. Maybe a few jerrycans.

 

Do you ever click the button on the end of your turn signal stalk ? I think your app is weird. Fill it up, carry a Jerry Can, run it until it's empty, recording facts as you go. fill with jerry can (known amount) go to gas station, fill oh, WHY ? what is PID ?

 

The only thing that displays in my car pressing the button on the end of the turn signal is the engine temperature. I've got a very basic car. The manual for my car in the MINI Guide app only has this one thing listed:

The app is simply displaying information from the OBDII connection. OBDII is a port for On-Board Diagnostics, which most cars have had since 1996, if not earlier.

PIDs are Parameter IDs you can access with an OBDII reader. PIDs are generally sensors or guages. There are PIDs which most cars send out, like Fuel Tank Level (as a %), Engine Speed and Vehicle Speed, there are also manufactuer specific codes, and BMW has lots of those, but you generally need to pay for an app that includes them.

So the number the app is showing is what the MINI is sending to it.

It is odd that when the fuel pump clicks off, the reading is 71.4%. I would love to put anotrher 30% in the tank, but since I don't want to damage anything, I'm not going to try to fill it too much past there.

But per @cjv2's suggestion, it would be useful to know how much gas those percentages actually represent.

I have enough data now to make a formula to predict what any percentage might be in actual litres, but since the gauge isn't linear and I suspect the gas tank isn't uniform (there's probably a lot of nooks and crannies) I may need more data points to be accurate.

 

Yeah, the gauge isn't linear and the gas tank isn't uniform. In the case of the gauge, my own observations have made it clear that it drops more slowly towards the top end than at the bottom. And unless the tank had a completely flat bottom and uniform sides -- so a cube, or brick, or cylinder, you get the idea -- a given vertical drop in in-tank gasoline level would not uniformly translate to the same amount of gasoline used. And we all know the tank is not shaped like a cube, brick, cylinder, etc. Exemplar attached (for my F56S).

Also, I happened to run the tank down pretty low recently, and a refuel, no top-off, put 9.9x gallons in the tank. The reading of the number of gallons in the tank immediately after that refuel, before pulling off, displayed by Bimmerlink, was a little over 11.5 gallons. Just to get folks arguing about capacity all over again.

 

my '15 MCS has about 5-7 different clicks on turn signal stalk, so I can't relate.

 

The Fuel Reserve warning showed up just before I made it home tonight. It showed at 10.4%, and just a few seconds later it dipped to 10.3%.

The app tries to calculate the range and was at 52kms, so maybe it's when the car calculates 50kms. What does it say in the manual...the message shows continuously when the range is below 50kms.

 

I haven't seen anything in the manual that specifies when the fuel reserve warning will kick on.

However, it does have this, which intriguingly correlates with your 50km hypothesis.