ah ok. Ill have to try it then, after my next fill up, if the gauge is still messed up, Ill add some. Thanks for the info, appreciate it.

 

Yeah, the fuel gauge is poorly designed/integrated. The only useful thing is watching how many miles you have left on the Tach selectable display, which is not entirely accurate but much more realistic than the gauge. The actual gas "gauge" is really bizarre in the way it is scaled, and it's not precise in the least.

I wonder if it's possible to get an analog aftermarket fuel gauge?

And you shouldn't need to use Chevron gas to get an accurate fuel gauge -- if it's true then all I can do is shake my head.

 

since the tank is under the back seat just take out the sending unit and use a stick like I did in an old pickup truck I once owned.. the tank was behind the seat so I kept a yardstick to to dip in there to see how much I had..
oh the good ole days

 

Haha noooo...its designed that way to give a bit of lee-way for lazy folks like me that refuse to fill up until its completely empty

On the R56 after 0 mi...it will go to 4 dashes (----)....

On my R53 it was 3 dashes (---) and they would count down if you kept driving....I haven't seen my R56 subtract any dashes though.

 

Modern gas, at 10% ethonol is a super solvent. As great a product as Chevron makes, it will not have any effect on this problem. It is a design issue backed up by a company who does not consider these things to be important.

If you have seen a BMW style sensor, you will see how the float is trapped at a fixed level for a long time. It is not a float on an arm like many other sensors that can use the expansion space to ride in. It does sound like large variances as some can run it below zero and still have a gallon. So, I guess I have to add poor quality control to the list.

Can anyone tell me the wires that form the circuit? level and limit switch? If I can get to them, I might make some readings and see if I could build a non-linear buffer. Just my luck it is all internal to the sensor and just a signal on the CAN to the computer who does the display. With no schematics, I am only guessing.

 

Not knowing any better, I routinely refill only when I'm down to the last red, blinking carrot and OBC says <40-60 miles to go.

One of the first things I wanted to know when I bought the car was how accurate the gauge was so I would know how much I could push it.

The first time I filled up, I put 13.57 gallons in the tank. I know it was topped off when I got it so 13.57 gal in 473 miles = 34.9 mpg. So I'll take the fuel tank capacity, subtract the 13.57 gal I just put in, and then multiply that times 34.9 mpg; that should give me the number of remaining miles in the tank. Compare that with OBC and see how accurate it is, right?

Now, what's the fuel tank capacity? Consult the online specs from the webpage: "2008 MC has 13.2 gal fuel capacity." WHA???? I just put in almost 13.6?? So much for that idea.

I keep a log of all kinds of worthless data, and my log shows that in my 58 fill-ups in just over 2 years, I have refilled with >13.2 gallons about 60% of the time. My max was 14.36 gal.

I've since found in the owner's manual that it says my '08 MC has a 13.2 gal gas tank "including reserve of 2.1 gal." (I'm still trying to wrap my head around that wording.)

The instance when I filled with 14.36 gallons, I believe the OBC was saying 19 miles to empty? 13.2 tank + 2.1 mysterious reserve - 14.36 gallons used = actual remaining tank contents of 0.94 gal x 37.9 mpg in this case = 35.6 theoretical miles I could drive to empty. OBC says 19. I'll call that close with a bit of a buffer.

Regardless, it's obvious A) the tank is larger than 13.2 gal, B) my OBC is pretty accurate, however C) I should get in the habit of refilling before it gets that low.

David

 

I suspect the OBC ( don't have one) is as accurate as the counter in the tach that gives MPG. It tells me I get 35 to 36. Fill-ups tell me I get 32. ( Guess my foot is heavier than David's). Even the 32 is a bit optimistic, as my odometer is several percent high compared to interstate mileage markers.
Unless David fills up at only one station who is a crook, which I seriously doubt, then his conclusions seem very sound.

I am not wiling to drive around a parking lot until it stalls to find out.

 

All posted specs say 13.2. ( Except AoL who says 10.1.) That must be before reserve. It must be 15.3 or David needs to have a serious discussion with his gas station.
Note the ACTUAL volume of the tank must be about 10% larger to deal with the expansion of gas when it warms up.

David, you did not say if fill-ups were normal quick and stop when the pump shuts off, or if you are trying to "top it off". Warning, that may plug the evap lines and cause a trip to the dealer for a plugged vapor separator or stalling due to vacuum lock on the pump. So, it is possible to put 14.36 gallons in an empty 13.2 gallon tank.

 

I've had mine down pretty low once or twice. no lights left on the gauge and the range readout says "---". Didn't actually run out though.

 

Motor,

How much did you put in in this condition?

I would assume if you went to the trouble of an autocrosser, you would want to know exactly to be as light as possible without a miss-fire. Making no implications, but it has been known in the past to put containers inside the tank to prevent starvation with very little heavy gas in there. Not that anyone would ever bend the rules like that.

 

FWIW My local mower shop (South east PA) takes samples of all the high test from the local stations and places it in little glass sealed bottles. They then let them sit on the counter in the shop. They only recommend gas from one station in our area ... and it is a BP station .... and the proof is looking at you on the counter.

The newer 2 cycle motors are very very touchy because of emission standards and gas quality is key to keeping them running.

You might want to get some small glass jars/vials and do some testing on your own. Let them sit for a month and then give them a look-see.

Bob

 

I've had by 2010 Clubman down to 1 red petal on the gauge and if I remember, it was showing under 20 miles until empty. I also filled my tank up to over 14 gallons the one time. Very odd considering it's supposed to a little over 13 gallons.

The gas gauge is definitely biased towards the full end of the tank. I will go about 90 miles until I lose the first light, then to 150 until the 2nd light goes out. It then seems to fall faster from there. It's like it's on a reverse logarithmic curve.

There is definitely some peculiarities about the gauge.

I'm not an engineer, but I don't think the type of gas should effect the reading of how much gas is in the tank. I do believe that a better gas and higher octane will provide better MPG's, though.

 

In that same situation, I've put up to about 14.6 gallons I believe.

So what am I sposed to be looking at to judge one is better than the other?

 

A little bit of chemistry.
Higher octane actually has less energy in it. BUT, it can be compressed further allowing slightly more efficiency. All things equal, lower mileage. In a real car on a real road, with a computer to adjust the advance, toss a coin.

"Gas Quality" I too am interested in his test. Dirt? Many small engines do not have fuel filters. Stupid. I add them to all my motors. I had my generator fail when I needed it due to dirt in the gas. Fixed the snow-blower I borrow the same way when it sputtered to a stop in 2 feet of snow. Gas stations do not have filters. Marina's do. Fortunately cars also have filters. I know of no other "quality" test you could so visually.

If this test is for dirt, then It says more about THAT station's tanks than the gas. All the gas comes out of the same pipe. It becomes the brand on the pump when put in the truck and that brand's additives are added.

AGAIN I ask everyone if you put in 14 gallons, is this letting the pump shut off, or are you topping it off? I wonder if there is a design issue with the venting for expansion space in the tank. Either topping it off or a vent size issue could allow overfilling.

Overfilling is bad. Gas comes out of the ground cold and pretty consistent in the weight and volume. It will expand about 10% from 60 degrees to 90. It has to go somewhere. In the old days, it spilled on the ground. Now it backs up through the evap control system into the vapor separator. Many cars will not drain this and it winds up throwing vacuum codes and may need dealer service to fix. Honda is infamous for this. All you need to do is stop when the pump auto cutoff does so.

I get 135 miles or more out of my first carrot, about 80 from the second. I blink and I am at 4. I got brave and went to 3. 11.6 gallons. Again, if someone would provide access to the wireing diagrams, I might take on building a non-linear compensator to make it a little closer. I do not know if this is a conventional analog system.

 

http://www.bmw-planet.com/diagrams/r.../r56/index.htm

 

Thanks. Took some work to get it past my security settings.
Looks like the level sensor is only a single analog sensor. So it is possible. Not even a warning switch in it.
Looks like it gets a regulated voltage, goes through the sensor, and the resulting current goes across a resistor where it is read. ( digitized I assume).

Gauge cluster is on the Can buss, so I need to fool the output of the sensor to tell the computer what to display. I guess track down the wires and put a tap on it for a voltmeter. Then fill up. Every 32 miles pull over and record the voltage. Don't know when I'll get around to it. Finding the wires is first.

 

quick question, when you run out of gas and you try to start the car...would the headlights flash at all?

 

I've gone as low as one bar and 6 mi remaining on the ODO and it still ran fine. Got me to the gas station.

 

No wonder Daddy always said fill at half a tank - especially on a MINI where half a tank on the gauge is more like a third a tank........

 

yep...know your car. Last week I got 108 miles out of the 1st bar.
When I just bought the Mini I got 80+ on the 1st bar. I would tell my friends this car is amazing on fuel...or the gauge is broken.

 

I had the same exact thing happened to me. Fixed under warranty. 2009 MC cabrio. I also had issue with fuel pump they are replacing as we speak. and with the cabrio grommet broken and wont fold all the way, but for the top they are denying warranty, stating that i used the top open while moving, i never did that!!!!!!!