You know what your fuel gauge does - it shows the level of gasoline in the tank (or at least it should). However, if you rely on it too heavily, you’re making a mistake. Fuel gauges are inherently inaccurate, even fresh from the factory and calibrated to spec.
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While you aren’t likely to run out of gas before it hits empty, you’re not getting an accurate perspective on your economy or how many miles you have left if you rely on it. Here are the reasons your fuel gauge (and every other person’s fuel gauge) is usually at least a little wrong.
Sending Units Aren’t Accurate
Fuel tanks are measured using a float system, which isn't tremendously precise. The sending unit is located inside the fuel tank and consists of a float connected to a thin metal rod that’s mounted to a variable resistor. Due to the design, the fuel has to drop below a certain level before the float will start to drop. If you pay attention to your gauge, you’ll notice it tends to stay full for a while after you top off. When the tank is nearly empty, the float also won’t extend to the bottom of the tank when there’s still fuel left, causing it to read empty when it’s not.
The Shape of Your Tank Isn’t Ideal for Readings
Fuel tanks are made of plastic or a like material and molded to fit into a tight space on your truck. Very often, it’s fitted to the truck so it has to form around frame rails, etc. What happens is, when the float reaches the halfway point in the tank, there may be more or less fuel in that area of the tank than the rest. This goes hand in hand with fuel sloshing and/or the vehicle's angle from horizontal that can impact readings, but that can happen even with a perfectly even tank.
Manufacturers Don’t Want You to Run Out of Gas
Most importantly, the fuel gauge is intentionally "off" about 3.5 gallons. This is so people on "E" will be able to drive about 30 miles to get more gas. Consider this a courtesy by Ford to keep you from sitting on the side of the road because you waited too long to get gas. Although, this isn’t fool proof, so fill up when you can!
What's The Solution?
The easiest way to address fuel gauge inaccuracy? Use your trip odometer. Odds are good that your truck consistently averages the same gas mileage...if you drive the same route every day, travel to the same places, etc., you'll get the same mileage from tank to tank. If you:
- Always fill your tank completely full when you buy gas
- Always reset your trip odometer when you fill up
- Pay attention to your average gas mileage from tank to tank
You should be able to look at the distance you've traveled on your odometer and estimate how much further you can travel. While this method isn't perfect, it's good enough to help you determine if your gas gauge is telling you the truth.
- Your truck has a 24 gallon tank
- Your truck averages 15 mpg
- You should be able to drive 360 miles on a full tank (24 x 15 = 360)
If your odometer says 300 miles, you've probably got 4 gallons of gas left in the tank. The fuel gauge is probably flirting with 'E', but you know you've got more range.
Finally, it goes without saying that there's risk involved when you decide not to trust your gas gauge. Consider yourself warned!