Hi All

I recently let the tank get way to low on my XKR. The light came on (I never let it get that bad) but I was late to work with zero time to even fill up, so I needed to finish the commute and just sweat the bad thoughts of bottom of the tank water/sediment making it through the fuel pump and to the engine. The car read 8 miles to empty by the time I filled up. Eeek. But then it topped off at 17.1 gallons!? This is a 19.9 gallon tank according to the specs. Do you think I really had 2.8 gallons left, or did the pump auto-shutoff way too early? Or is that spec a little over zealous? The only test I could think of would be to run it to empty, but I don't think my curiosity is worth the cost of a new fuel pump replacement.

 

Just for curiosity I continued to fill the car after the auto shut off at the pump. I was able to put in almost 3/4 of a gallon. The guage stayed on full a lot longer than it usually did. If I stop at the auto shut off the number of gallons delivered is pretty close to the cars "fuel used". I rarely let the car go below 1/2 a tank. Jack

 

They are never accurate, last time my light came on and I filled up, I put in just over 15 gallons or so, I call gas guages 'Guess Guages'. My old vette was even worse, it should 1 bar (empty) and I put in 16 gal. and the tank is a tad over 20 gal. if I remember right.

 

1) The pump always draws from the bottom of the tank, no difference empty or full. People that say you'll suck up dirt, water and/or other detritus will probably also tell you the fuel is used to cool the pump and a case could be made against those that chronically 'run on empty'. However, in-tank pumps are typically mounted vertically, at about mid-point in the tank. So you can also shoot that theory in the fanny.

2) 19.9 gallons is the spec but that's a completely dry system. Subtract roughly a gallon for the pump's inability to move around in the tank, sniffing out and sucking up stray puddles. Take into account the amount in the pump itself, the filter(s), lines, etc.

3) One should never fill past the auto shut-off, you'll just be asking for trouble. A lot of the evaporative emission system can be compromised from fuel saturation caused by over-filling. But hey, it's your money, do what you want.

4) I have yet to see any car that ran better empty than full. ;-)
(it happens to the best of us)

 

Everything Beav said. When I pulled my tank a few weeks ago there was no dirt or debris on the bottom of the tank. The pickup is right at the very bottom, so any dirt is going to get sucked up and sent into the fuel filter.

The bottom of our fuel tanks are completely flat from left to right. If you're on a slope or going around a curve the fuel is all going to go to one side of the tank and the area around the fuel pickup is going to be fuel free. I saw that first hand when I removed my fuel tank a few weeks ago. Then, after I put everything back together I put a gallon of fuel into the tank. I was driving to the gas station to get more fuel and I went around a curve. The engine cut out, but as soon as I straightened out it started running again. The fuel had shifted to one said of the tank and there was no fuel at the pickup.