Q: My husband freaks out if the gas light ever comes on (it only happens once in a blue moon). I tell him you can drive about 50 miles after the light comes on. He doesn't believe me. Since we don't want to actually test my theory and risk being stuck without gas, I thought I'd write and ask you guys what you think. So? — Liesa
RAY: Well, there certainly is SOME margin for error built into fuel gauges. How much varies from car to car. But I'd guess that the average low-fuel light comes on when you have about an eighth of a tank left.
TOM: There are two ways to find out whether that's true for your car, Liesa. You already know one way. You drive until you run out of gas, walk 50 miles home, and then say, “Honey, I told you!”
RAY: But there's an easier way to figure it out. Go to the back of your owner's manual and, in the “specifications” section, look up “fuel capacity.” Let's say your gas tank holds 16 gallons.
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TOM: Then, with your husband not in the car (no need to unnecessarily drive up his blood pressure), drive until the low-fuel light comes on. Then go to a gas station and fill the tank all the way up.
RAY: Now, subtract the amount the tank took from your fuel tank capacity. In other words, if the tank holds 16 gallons, and you just filled it up with 14 gallons, you know there are two gallons in reserve when the light comes on.
TOM: You may want to run this experiment several times to maximize your data and minimize the measurement error.
RAY: Now, how far will that remaining gas take you? It depends on the actual quantity of gas, your gas mileage, and what kind of driving you're doing.
TOM: But you know that however many miles you can go until empty, your husband will still be freaking out. Some people are just less inclined to enjoy surprises. Especially when they involve getting stranded and passing through the digestive systems of wolves.
RAY: So, for his sake, fill it up before the light comes on. Don't torture the poor guy – as enjoyable as that may be.