1) Gas guages aren't linear. They could be, but most (all?) aren't. One bar at the top isn't the same amount of gas anywhere else on the gauge. This has to do with the shape of the gas tank, and how fuel senders work.

2) Fuel capacities are exact.... For the tank! But all the hoses and the like add some capacity, about a half gallon or so.

3) There is some wisdom in the "dirt at the bottom of the tank" arguement, but with sealed fuel systems, it's a lot harder for dirt to get in there (unlike 60s american cars, where it came equipped that way from the factory!)

4) But for all of you you advocate filling half way through the tank, you do know that you've effectivly halved the range of the car, and that you will spend almost twice the time at gas stations as those of us that let the tank get almost to empty. Personally, I like to spend my time other places than gas stations!

5) Station pumps are regulated, tested, and cerified. In my entire life of 43 years, I've NEVER heard of pump calibrations being off. That's not to say it's not possible, but it's not likely.

6) The guage got more accurate over time? Huh? This I've never heard of. Some mileage estimaters use how the car has been driven over a bit of time to figure out average mileage. But I'v never heard of a self calibrating gauge!

Matt

 

2)Fuel capacities of tanks include room for thermal expansion (they don't want to overflow to the carbon filter) and other "safety" space. Unless you know precisely how much that is, and it's not included in the advertised capacity, you won't know the total capacity of the tank.

4)Pumps in the tanks WILL get hotter when the gas isn't high enough to adequately cool the pump., so WILL get less lifetime. I've changed a few pumps-not fun. Don't want to do it. Big hassle. There is absolutely no other heat dissipation path from the pump other than to the fuel or air in the tank. The warmer the pump gets, the worse it is to the innards. Easier to try to avoid bottom 1/4 at least some of the time.

5)I've seen at least a couple of expose's on local TV news where they go around and check pumps. MUCH of the time they're off. The state is supposed to regulate, but does so rarely. Each time in three different states that I've seen an expose' (NC, CO, TX), the pumps are supposedly regulated, tested, and certified. The problem is that these states just doesn't have the resources, and so it just plain doesn't happen. Some pumps were NEVER tested in each of the expose's. So I believe in the pumps being off. If a random spot check reveals a high probability of error, and there's little evidence pointing to the contrary, to me it's reasonable to think the odds of a pump being off are pretty good.

California could very well be different. If so, good for you!

Of course, you could take an exact measuring container-one you know is precise, not just a jerry can or some other gas can, and check your stations yourself. Tell us what you find. That data point would be an interesting comparison to what I've seen.

 

This is really not true. Think about it. The gas is ALWAYS being sucked from the bottom of the tank along with these mystery contaminants no matter if you have a full tank or a nearly empty one. Since this is the case, those particles do not wait for the last few ounces in the tank before they move into the fuel line.

Gas is also always sloshing around, mixing these contaminants throughout the gas while driving, so you are always sucking up any contaminants into the fuel line.

This is why all cars have fuel filters.

 

Also, fuel pumps in the US are not required to compensate for the temperature of the fuel. They have lobbied against it for years.
Here's a site I don't endorse, but they have a good write up about it. http://www.citizen.org/pressroom/release.cfm?ID=2334

One more variable for the equation.

 

thanks

 

I'm always left in doubt when ever someone addresses a problem with a one thousand word essay on an internet forum. Very often these lengthy explanations miss the simple truth. I have never owned a car with a gas gauge that read half full when in reality the tank was close to empty. That is what I have been experiencing with my new mini. I use the same gas stations I have been using all of my life and I don't think they are the source of the problem. until I get a chance to speak with a Mini service center I’m going to assume that there is something wrong with the gas gauges in some of the 07 Mini Coopers.

 

I'm hoping to take delivery of my 2007 MC next week, and this gas gauge/tank capacity issue is on my list of questions to discuss with my MA.

 

This thread is getting off mark, I just wanted to make the observation that I could put "probably" a gallon or more in the tank than the stated capacity, I don't beleive either that in my case at least the pump was cheating me, we have strict testing in my county, well annyway I also noticed that I drove 68 miles before the first light went off on the gauge after filling up, and I've driven 196 miles and only 4 lights are off, I know my wifes car will linger right at half full for like 100 miles before dropping fast, just an observation.

 

Your right Mininovice, the thread has strayed.
The newer pumps that are being installed have a vapor scavange system to comply with the Clean Air Act. When you squeeze the handle on these guys they suck in air for a second, then they start dispensing fuel at a fast pace. Makes it difficult to top off. The days of "bumping" gas into your tank a few pennies at a time to top off are over.
They even have a sticker on the pump instructing you not to top off.
I like topping off my tank. Even though I pay for the fuel, I see all the miles I drive with the tank indicating full as free miles.
Silly aint it?

 

Man, you're not kidding about that. In my old Mercedes, the engineers at least *tried* to make the gauge more accurate by placing the markings at uneven intervals to better match the non-linear motion of the needle as the tank emptied out.

As a result, there's not even a needles' width of black space between the "Full" and "3/4" mark, but the space between "3/4" and "1/2" takes up half of the gauge! The space between "1/2" and "1/4" is only slightly smaller, and the space between "1/2" and "Empty" is about two needles' widths.

 

if you're worried about your senders, get a factory scan. It will talk to the sender control module and that will report if there is a short or an open. With the new cars, I don't know if they use the same sender as the last model, but many (including myself) have had issues with it.

Short enough?

Matt

 

I'm more confused now than I was at the start of this thread regarding the capacity of the gas tank. :impatient So, I'll just assume my 2007 MC has "approx. 10.6 gallons including the reserve" as stated in the manual.

 

I was assuming the same thing until my 2nd fill up when at half a tank I was able to pump almost 10 gallons! At first I thought maybe the tank is 20 gallons but the book says 10.6 so i'm going to assume its a gauge error.

By the way half a tank is a totally unacceptable and dangerous margin of error for a gas gauge. I have never had a car with a gauge that far off.

 

After you get it checked out, please post and let us know the details. Thanks, CeeTee.

 

I would agree with you for the most part, but in my Lexus IS, the gas guage is horrifically accurate. Each tick mark (evenly spaced) on the gauge represents one U.S. gallon of fuel. And when it hits empty, you are out of fuel. This is the first car I have seen with such an accurate gas guage.

With the advent of digital gauges (whether or not they have a needle or some type of digital readout, they are driven digitally), it is very easy to create a ramp for the gauge which compensates for the shape of the fuel tank. Take a 360 degree slice of the profile of the tank, then average the profiles to get the ramp. With everything being designed in CAD these days, there really is no excuse for a gas guage to not be accurate.

Even if it is analog driven, the coil can be adjusted to compensate for the float travel to simulate the tank profile.

 

If you REALLY want to know where things are at on your car, have someone follow you with a gas can or have some in the boot and see precisely when you run out. Then you really know where EMPTY is relative to the gauge.

Another trick is to reset the trip odometer when you fill up, and figure out how far you usually go before you fill again. Then you can use the odometer to double check the gas gauge and OBC.

 

Here's a great picture and articles on the subject
http://www.sciencedaily.com/releases...1023120710.htm
http://www.npr.org/templates/story/s...toryId=5304258
http://www.fredericksburg.com/News/F...5312001/296679
http://seattlepi.nwsource.com/local/...aspumps27.html
http://www.wtopnews.com/?sid=605176&nid=428&pid=0

another problem I haven't seen mentioned yet is that you may not always get the octane you're paying for. The last article stated 117/159 inspected stations failed to deliver the correct octane.

 

That's interesting - I wonder if the 117 that didnt deliver the correct octane were just a little bit off (like the gas tested at 90.8 octane instead of the advertised 91), or if was something egregious like all three nozzles dispensing 87-octane?

 

I've seen tv news reports showing the underground tanks containing the wrong grade
http://www.jsonline.com/story/index.aspx?id=317263
http://www.npnweb.com/daily/news.asp?a=564214
http://mlive.live.advance.net/news/f...1_shorted.html

 

Anybody brave enough to drive one of these little suckers untill it runs out of gas and stops, then fill it up to see how much gas goes in the tank??

 

Update:

I called my Mini service manager last week and informed him of the problem I was having with my gas gauge. He asked me to drive the car to almost empty and to measure the amount of gas the car takes to fill up. To my surprise after following his instructions I was able to pump 13.2 gallons into the tank. So I guess some of the 07 MC s are equipped with the 13.2 gallon tank instead of the 10.6? Has anyone else noticed this?

This also explains why my car was able to hold so much gas at what I assumed was half a tank.

 

CeeTee1:I am going to get gas today, I bet I'll be able to do the same thing, I'm 2 bars lower than when I filled up with 10.2 gallons, I'll report back what I find.

 

I picked up my MC today. When my MA came back from filling the gas tank I asked him about this issue. He checked the receipt and said my car took 12.5 gallons. So, obviously, the tank isn't 10.6 gallons. He said MINI is vague about the size of the gas tank...I don't understand why, but that's what he said. He added that it's his understanding that the tank is the same size it was before, although he said 13.8 gallons and I thought it was 13.2. I still don't understand why the manual is wrong, though.

 

I called my Mini service manager today and told him about my findings. He responded by stating that the 10.6 tank size stated in the book is either a misprint or a standard for European cars and that in fact all 07 MC's in the U.S. are equipped with a 13.2 gallon tank.

Now that this issue is resolved i'm sure glad I don't have to take my car in to have the gas gauge replaced.

 

Great info I pumped 12.5 gallons yesterday untill full so thank you for the confirmation!