Can You Trust Your Fuel Gauge?

March 20th, 2014

miles to empty

I’ll just get gas when I go out later tonight.

Sure, the gas light came on and I’m 12 miles from home, but I’ll make it and I have to go out later anyway and will be closer to a gas station tonight.

That’s not an uncommon thought for me, and it’s one of the problems of living in an area that’s at least 15 miles from a gas station. Earlier this week it happened to my lovely girlfriend. It would have been fine, but plans changed, and she didn’t make it out to the gas station that night. She forgot about the low-fuel situation until leaving home in the morning, late, for a meeting at work 40 miles away.

Her Subaru told her she had 50 miles to empty. She called me with her quandary:

Should she trust it and power through in hopes of coasting into work right on time? Or should she risk being late and pulling off the Interstate to fill up?

Basically the question boils down to this: How reliable are fuel gauges and mileage displays?

My Audi has a constant countdown of mileage remaining until the tank is empty. When I fill up, the reading says I have 475 miles of driving available, but changes drastically depending on the type of driving. When I’m cruising the Interstate, that number can jump to 520 miles or more. When I’m stuck in city traffic the number quickly drops to 460 or less. The point is, it constantly adjusts, and I usually drive about 375 miles before I start thinking I should fuel up.

Theoretically, yes, I could drive 475 miles on a tank, but that assumes I run it dry or risk undo stress by pushing too far.

I’ve been surprised at how much fuel is actually left when the needle points to E. The Audi holds about 26 gallons of gas, but the last fill-up took only 19 gallons even though the needle was in the red.

I kept that in mind as we discussed the Subaru’s pending fuel emergency. As we spoke, the range dropped to 40 miles, and she still had 35 to go. Fuel gauges are not an exact science and provide more of a rough idea of your fuel situation. For those reasons, I had her pull off the highway and fill up.

The Subaru holds 18.5 gallons of fuel, and it took just under 18 to fill up. Had she trusted the computer, she probably would’ve been stranded on the side of the road.

How much faith do you put in your fuel gauge?

-tgriffith

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