Quote:
Originally Posted by PR3CI5N
Once the dash says 0 miles left, you still have about 30 mles of driving before you drain your reserve.
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I'm not sure this is right. I think the reserve is the part of the tank that's used when the idiot light comes on, not something that kicks in when the needle reads 0. My M3's manual says I have a 13.3-gallon tank plus a 3.3-gallon reserve. When I put gas in immediately when the idiot light came on, it takes....13.3 gallons. The one time I filled it just barely over 0, it took right around 16 gallons.
Quote:
Originally Posted by AndreyT
It shouldn't hurt a properly designed car. However, there's a popular belief that due to a design error BMW cars should not be allowed to run lower on fuel that 1/4 of a tank. Otherwise, the service life of the fuel pump might get shortened considerably. Some people even claim that BMW service technicians recommend to fill up before it gets lower.
While BMW is indeed infamous for its fuel pump problems (that stretch far beyond "HPFP failure" issue), it is not clear whether this design error has been fixed or not in modern cars.
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I don't think it's a design error. BMWs have their fuel pumps inside the actual fuel tank, which means that one reason you're not supposed to use the reserve is because the pump relies on being submerged in gasoline to be cooled, so if you're in the reserve and driving hard and/or in a hot climate, then in addition to other potential problems, you risk overheating your fuel pump. That's not so much an error as an inherent property of that design. I don't know enough about fuel pumps to know the advantages of locating the pump inside the tank rather than elsewhere, though I'd bet one of them is not having to have a separate cooling mechanism for it.