Gas Tank Level Theory

Elle · 2006-01-12T04:32:26+00:00

I have been watching my 91 Civic's mileage particularlyclosely since about October. This includes, for theoverenthused, watching the fuel tank gage. A few times Ihave thought to myself, "Darn, it's reading just abouthalf-full, and I usually have at least X miles by thispoint. The trip odometer is at more like X-50 miles rightnow." So I would predict that the next fillup will yieldstats indicating really bad mileage. But on the contrary,apart from a few weeks where I had the timing messed up, itlooks good, for winter.As people have indicated here recently, gas pumped in thesummer from a nice cool underground tank (typically) expandsonce in the car's tank and while warming to ambient. Thismakes sense. In this vein, could it be that, while drivingin the summer, the fuel tank gage reads particularlydisproportionately to the lbs. of fuel consumed? That is,the actual level in the fuel tank goes down literally moreslowly from full tank to half, because the gasoline in thetank is simultaneously expanding (due to temperatureincreases). By the time the driver reaches a half tank orso, the gasoline isn't expanding as quickly, because itstemperature is pretty constant.I recall times in the summer where my Civic has achievednearly 300 miles by the time the gage reads half full. Thenit drops very quickly. In winter, I can't get anywhere nearas many miles on the trip odometer by the time the tank ishalf full. Still great mileage; just totally out of whackwith the fuel gage.Anyone else notice this? Comments on this theory?

Jan 12, 2006 26 Replies

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Elle 20 years ago

"Remco" wrote snip

(expansion, fuel

that 30-50

I agree, so far.

recording mileage

gauge. It

accuse it.

I think we're having a miscommunication. What I'm challenging here is whether the gage reads more proportionally to the actual weight of fuel in the tank in the winter rather than summer. E.g. in winter, I get about

220 miles by the time the gage indicates half-full. In summer, by contrast, I get about 270 miles.

Roughly.

worse as they

tank shape is

linearity

another small

also be that

Right.

It's not something I'm losing sleep over. Just something that might be worth mentioning when people come here complaining that their fuel gage doesn't read in much proportion to the fuel in the tank.

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Elle 20 years ago

"Larry J." wrote

full

though

9.5

gasoline.

Not in my neck of the woods.

In some parts of the country, yes, there is a significant difference in gasoline "blends."

mileage.

Oy.

We're having a miscommunication.

you have

based on

average.

That's exactly what I do.

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SoCalMike 20 years ago

thats what i do, too. i also knew on my last trip to laughlin that i can usually make it there on a tank of gas.

almost all the way there, gauge is reading low. trip odometer says something like 285 miles. 11.9 gal tank, i usually get 32mpg. (380 to a tank?)

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Larry J. 20 years ago

So, how many gallons did you use for 285 miles..?

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Remco 20 years ago

Exactly - that's the interesting part.

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SoCalMike 20 years ago

i ferget. turned out to be something like 25mpg. incredibly low, but thats running close to 100 at times, with the A/C, and in 3rd or 4th gear. definate mileage killers!

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TE Cheah 20 years ago

| Still great mileage Impossible w-o changing your exhaust*manifold & spark cables.

Honda fits only short branch ( 4 into 1 pipe ), cheap & heavy cast iron

for its engines

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