Gas gauges...WHY after a 1/2 tank they drop like a rock?

[Charged]

Ive never seen a gas gauge that doesent do this, so it has to be that they ALL suck. But it takes them forever to get down to a 1/2 tank, but when they hit that mark, they drop like a rock. Is it that you get better gas mileage with over a 1/2 tank?

Charged

[HeavyFuel]

The answer is often the way the gauge works. A float in the tank controls the gauge and, according to howstuffworks.com, a full tank often submerges the float. The needle doesn't start moving down until the fuel level catches up with the float's uppermost position.
Similarly, the float often doesn't go as low as the empty tank, meaning you usually have a gallon or two left even when on "E."

[69hemi]

The shape of the tank also dictates how the gauge reads.  If the tank is wedge shaped the as will be used faster as the level approaches the bottom.

[TruckDriver]

My Ford van and my Chevy Blazer do that too.

[derailed]

I put a new sending unit in the car last winter and it always reads a quarter below whats actually in the tank, never goes over 3/4 according to the gauge.   

[JimShine]

My new tank and sending unit reads 50% of what it should.

[Ghoste]

My guage will stick at about 3/8 of a tank.  The first times it happened, I thought, "wow this thing is getting great mileage all of a sudden".  Then I clued in.  Didn't run out, but there comes a point where you KNOW it isn't getting that great mileage.  Now after it hits the 3/8 mark, after I drive it for a while, I just give it a gentle tap.

[Chargerguy74]

I thought mine was getting awsome mileage too. That was until I found out that when the tank was empty, the gauge was at 3/4. I usually get 25 miles or more out of my vehicles after the gauge is on empty.

[Blown70]

Well my gauge stuck and the electonics said I had 48 miles to go...... HAHAHA..... In 20 degree weather that was NOT nice.   Anytime mine hits less than 1/4 I am filling up.... That crap is not going to happen again.

[Highbanked Hauler]

I put a new sending unit in the car last winter and it always reads a quarter below whats actually in the tank, never goes over 3/4 according to the gauge.     

    Mine does the same thing but it gets more accurate below half full.When it is on the empty line, it is empty cause I have put 18 gallons in it a couple of times.

[bluesfool]

I put a new sending unit in the car last winter and it always reads a quarter below whats actually in the tank, never goes over 3/4 according to the gauge.

At least I know I'm not the only one with this problem! I installed my unit this past spring.