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Can anyone explain why the fuel gauge indicates "full" with only 9 gallons of gasoline in the tank bladder?

I own a 2004 Prius which has under 2,000 miles on the odometer.

As you know, the fuel gauge shows 10 blocks when it is full. The capacity of the fuel tank bladder is 11.9 gallons. Therefore, each block should represent about 1.1 gallons.

I fill the tank only when the fuel gauge is down to 1 block. Today, the single block was flashing indicating critically low fuel. According to the Prius Manual, the flashing block indicates 1 gallon or less.

Every time I fill up, the tank will accept between 7.0 and 8.0 gallons - no more. After each 7 to 8 gallons, the fuel gauge shows a full tank with 10 blocks.

It seems logical that adding 8 gallons when the single block is flashing should mean there are 9 gallons in the tank. With 9 gallons of fuel in an 11.9 gallons tank, the fuel gauge should register a partially empty tank or about 8 blocks.

I have brought this to the attention of my Toyota Carlsbad dealer. The mechanic can find nothing wrong.

My concern is practical. If my fuel gauge is not registering correctly, can I trust it on a long road trip?

Can anyone shed some light on this? Does anyone have a logical explanation? All comments would be gratefully accepted.

Thanks....

Harrison
 

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> Can anyone explain why the fuel gauge indicates "full" with only 9 gallons of gasoline in the tank bladder?

The gauge was calibrated to provide indication of a 9-gallon non-emergency capacity. You actually have more gas inside, but it won't show you that... intentionally. The reason is to prevent you from ever running out of gas, since doing that is very hard on the battery-pack.

Too many pushed too far, with the classic Prius. Consequently, there were a disturbing number of out-of-gas incidents reported. So with the new Prius, Toyota decided to decrease the measurement scale. That obviously worked. However, the behavior baffles new owners, especially since they think the gauge is linear.

The gauge is actually non-linear. That means each block represents less gas as get closer to empty, not a consistent amount. The benefit is greater precision as you get closer to empty.

Also note that the blinking of the last block is not a warning, it is an indicator (which coincides with the "Add Fuel" message shown on the Multi-Display). It is not intended to be interpreted the same way as the "almost empty" light in a traditional vehicle. Instead, it is telling you that it would be wise to fill the tank within the next 20 to 30 miles. So you can actually push beyond that range (for emergency use), but it is not recommended since the bladder reduces overall capacity sometimes (making capacity beyond 9 gallons difficult to measure).
 

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So far, I don't recall driving my 2004 down to "blink" (yet?). However, we hit the blinking bar and corresponding message on the 2003* today on the way to refuel; it took 10.855 gallons before auto shut-off, so theoretically just over a gallon left in the tank on that one.

* Not my car, so don't blame me for letting it get that low... ;)
 

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On our recent car trip, we ran out of gas. We ran out of gas only 2-3 miles after the blinking began. Fortunately, we were able to make it another mile and a half to the next exit on battery alone (not good, I know). There have been news reports in our area that the ethanol gasoline has been affecting the gas sensors on some vehicles. (I ran out of gas in my Chevy van and I have an analog gauge with a low fuel light that had gone on a few miles earlier--I used to be able to go 80 miles after the low fuel light came on).

Has anyone else heard of this (or any other critical info) with ethanol? Our city is in a legal battle trying to stay the EPA requirement that all fuel sold here be of the ethanol added variety....
 

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I had also heard reports of gasoline effecting fuel gauges, but as I heard the story, it wasn't ethanol but sulfur compounds.

Tau Zero
 
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