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      10-29-2014, 05:44 PM   #1
stevearmstrong
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Fuel reserve light comes on with a quarter tank left!

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So I do a lot of city driving and this results in a very low fuel efficiency and a low corresponding range, when driving solely in the city. Just got my car and this first time emptying the fuel tank. With about a quarter tank left and a range of 50 miles the fuel reserve indicator came on.

This seems a little ridiculous to me. First, according to the manual, I thought the fuel reserve comes on when the range is less than 30 miles, not 50.

Second I have a quarter tank of gas left and am not actually at risk of running out of gas. Typically in other vehicles I thought the low fuel light comes on when there is 1 gallon left.

I assume if I start driving on the highway again the range would increase and the low fuel warning would increase and the warning would go away.

Why is this based on range and not the actual volume of fuel remaining? The indicator should come on when the fuel is actually low not when some inaccurate calculation of the range is low. At least use some sort of combination of the two rather than just this method.

Anyone else experience this and any way around it?

Is it possible that something is actually wrong w the electronics?
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      10-29-2014, 05:45 PM   #2
stevearmstrong
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FYI I'm coming from an 07 e92.

Never had this issue w that car. It also seems the range calculations for the m235 are way off and swing wildly. Maybe this is contributing to it.
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      10-29-2014, 05:48 PM   #3
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Warning comes on at fifty miles of range left, but it's a warning without a nag screen (just the warning triangle). At 30 it will warn again and iDrive screen will have a nag warning until you refill.

A new car will have lower MPG, but most cars seem to be miserly on gas on a full tank and then appear to use up more at half tank. Not sure why, but seems to be the case with most modern cars, including BMW.
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      10-29-2014, 05:53 PM   #4
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Another thing I've noticed in my car is the sensor is located at the front of the tank. This I've concluded by noticing fuel range going up and down hill. When going up a hill, range drops. On down hill, it starts to increase.
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      10-29-2014, 06:03 PM   #5
stevearmstrong
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Ya I've noticed some of the same things as well. As far as using gas more quickly as the tank empties goes, it's possible that the gradations are not as accurate as the tank becomes more full. For example I know even though the gauge is on full I can still pump a few extra gallons into the tank.

When returning rental cars I always monitor the gauges rather than just filling up and I almost never actually return the car w a full tank of gas even though it shows as full.
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      10-29-2014, 07:10 PM   #6
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If you have a range of 50 miles, you don't have a quarter of a tank no matter what the gauge says. Do the math. If the range is 50 miles, that's about two gallons. Your tank is bigger than 8 gallons. Haven't you ever noticed how when you fill the tank, the gauge seems to show full forever but when you get below a half tank, it drops like a stone? This is true of all cars. I think manufacturers do it to make you feel good about the mileage you're getting (or appear to be getting). "Hey, look how much I've driven and it's still full! Wow!" LOL
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      10-29-2014, 10:13 PM   #7
espo
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According to the manual the gas tank is listed at 13.7 gals, if you are driving around the city a lot and "enjoying" your car you may be getting about 16 mpg (that's what I get going back and forth to work which involves a lot of stop lights, traffic, and driving through neighborhoods). Using those numbers, if the light comes on at 50 miles (which I have also seen), then you would have about 3.1 gals left, which works out to 0.23 of a tank (almost exactly 1/4). So a completely conceivable situation.

The better question, why did they put in such a small gas tank.....
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      10-30-2014, 12:30 AM   #8
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Wow, if you're only getting 16 mpg that's a range of only 200 miles. I ordered a 228 so I'll get better mileage, but I'm gonna miss the range on my MINI. I get 30 mpg mixed driving and it has a 13.2 gallon tank so a range of almost 400 miles.
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      10-30-2014, 12:34 AM   #9
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No way it's 16mpg. Maybe if the engine is still breaking in, but you're talking M3 with a V8 mpg range there...
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      10-30-2014, 01:06 AM   #10
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Quote:
Originally Posted by hyperzulu View Post
Another thing I've noticed in my car is the sensor is located at the front of the tank. This I've concluded by noticing fuel range going up and down hill. When going up a hill, range drops. On down hill, it starts to increase.
I think the calculation is based on the fuel injector's duty cycle, which would explain numbers decreasing uphill, increasing down. But to verify you will need to run the next tank out at full throttle. All the time. ;-)
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      10-30-2014, 05:54 AM   #11
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Quote:
Originally Posted by hyperzulu View Post
No way it's 16mpg. Maybe if the engine is still breaking in, but you're talking M3 with a V8 mpg range there...
I'm taking sitting in traffic and taking 15-20 minutes to go less than 4 miles...
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      10-30-2014, 10:38 AM   #12
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Quote:
Originally Posted by espo View Post
I'm taking sitting in traffic and taking 15-20 minutes to go less than 4 miles...
This is exactly what I'm talking about. Sometimes worse. 25-30 minutes to go 3.5 miles. Traffic is a bitch and mpg just plummets.


The range entirely depends on what kind of driving I'm doing for example in my 335 if I'm in the city and fill up after only having driven in the city for the past week the range will be ~225-250 miles.

However, if I'm on a road trip and filling up on the highway after driving for a couple hours the range has been as high as 475 miles.

My point was just that it would be nice if the low fuel indicator light was triggered by the actual amount of fuel left, not some inconsistent wildly fluctuating range calculation.

It is after all a "Fuel Reserve" light, not a 'Low Range" light.
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      10-30-2014, 10:40 AM   #13
stevearmstrong
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Quote:
Originally Posted by espo View Post
According to the manual the gas tank is listed at 13.7 gals, if you are driving around the city a lot and "enjoying" your car you may be getting about 16 mpg (that's what I get going back and forth to work which involves a lot of stop lights, traffic, and driving through neighborhoods). Using those numbers, if the light comes on at 50 miles (which I have also seen), then you would have about 3.1 gals left, which works out to 0.23 of a tank (almost exactly 1/4). So a completely conceivable situation.

The better question, why did they put in such a small gas tank.....
Well I'm glad I'm not the only one that's getting such terrible mpg. That's real city driving for you I guess, not the "City" driving that is commonly used for advertised mpg calculations.
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      10-30-2014, 11:10 AM   #14
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Quote:
Originally Posted by espo View Post
I'm taking sitting in traffic and taking 15-20 minutes to go less than 4 miles...
OK, that's different, I suppose. I mean, I can do 0mpg by just turning on the car and leaving it in park until I run out of gas. I don't think one is going to run out and buy a used Hummer and justify it as getting better gas mileage.
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      11-03-2014, 11:27 AM   #15
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Quote:
Originally Posted by espo View Post

The better question, why did they put in such a small gas tank.....
Agree 100%
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      11-03-2014, 12:35 PM   #16
hyperzulu
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The fuel range tests must be performed with a certain amount of gas in the tank. Gas has weight, which adversely affects MPG. Not sure if this is part of the reason, but it's possible.
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      11-03-2014, 01:15 PM   #17
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Quote:
Originally Posted by espo View Post

The better question, why did they put in such a small gas tank.....

Best part is the tank appears to be larger in other countries. US cars got screwed.
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      11-03-2014, 01:19 PM   #18
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Quote:
Originally Posted by hyperzulu
No way it's 16mpg. Maybe if the engine is still breaking in, but you're talking M3 with a V8 mpg range there...
My mileage has SUCKED on this car. Around 17 mpg and I drive on the interstate to work. (Granted its Atlanta). The car as 4300 miles on it now.
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      11-03-2014, 01:32 PM   #19
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Strange. My N54 gets better mileage than that on my commute. The N55's I have driven as loaner vehicles have given me at least 21mpg and better on my commutes. Are you guys driving 6spd?
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      11-03-2014, 02:06 PM   #20
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The fuel light on my 128i usually comes on with about 3 gallons left in the tank... 14 gallon tank and I always fill up shortly after the light comes on and it is usually ends up being around 11 gallons put in the tank to fill it up. According the the pumps measurement of course lol
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      11-03-2014, 02:17 PM   #21
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Pay close attention to the remaining miles countdown, I ran out of gas while it displayed 3 miles left. My e90 used to give me better than 10 additional miles when it displayed -- (o) miles. Yes the tank is pretty small.
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      11-03-2014, 04:35 PM   #22
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Quote:
Originally Posted by ciwhamc View Post
Best part is the tank appears to be larger in other countries. US cars got screwed.
I don't believe that they fit different tanks for different markets. We have the same 52 litre (13.7 US Gallon) tank here in Australia.
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