Re: Gas Tank Level Theory
"Elle" <honda.lioness@earthlink.net> wrote in message
news:uZkxf.8215$M%4.5531@newsread3.news.atl.earthl ink.net... >I have been watching my 91 Civic's mileage particularly > closely since about October. This includes, for the > overenthused, watching the fuel tank gage. A few times I > have thought to myself, "Darn, it's reading just about > half-full, and I usually have at least X miles by this > point. The trip odometer is at more like X-50 miles right > now." So I would predict that the next fillup will yield > stats indicating really bad mileage. But on the contrary, > apart from a few weeks where I had the timing messed up, it > looks good, for winter. > > As people have indicated here recently, gas pumped in the > summer from a nice cool underground tank (typically) expands > once in the car's tank and while warming to ambient. This > makes sense. In this vein, could it be that, while driving > in the summer, the fuel tank gage reads particularly > disproportionately to the lbs. of fuel consumed? That is, > the actual level in the fuel tank goes down literally more > slowly from full tank to half, because the gasoline in the > tank is simultaneously expanding (due to temperature > increases). By the time the driver reaches a half tank or > so, the gasoline isn't expanding as quickly, because its > temperature is pretty constant. > > I recall times in the summer where my Civic has achieved > nearly 300 miles by the time the gage reads half full. Then > it drops very quickly. In winter, I can't get anywhere near > as many miles on the trip odometer by the time the tank is > half full. Still great mileage; just totally out of whack > with the fuel gage. > > Anyone else notice this? Comments on this theory? > > It seems plausible. The volumetric coefficient of expansion of gasoline is about 0.1% per degree C (http://tinyurl.com/bpp2k) and the constant circulation of the fuel through the engine compartment (through the fuel pressure regulator) and warming by the in-tank pump could plausibly add 30 degrees C or more to cold fuel within an hour or two. That would expand 10 gallons to about 10.3 gallons, so if you've only burned a gallon or two in that time it could appear as a noticable increase in fuel efficiency. If there is less fuel in the tank, the same amount of heat will warm the fuel faster. Maybe the fuel guage reads slightly higher as the passenger compartment warms up? Mike |
Re: Gas Tank Level Theory
Michael Pardee wrote:
> > > It seems plausible. The volumetric coefficient of expansion of gasoline is > about 0.1% per degree C (http://tinyurl.com/bpp2k) and the constant > circulation of the fuel through the engine compartment (through the fuel > pressure regulator) and warming by the in-tank pump could plausibly add 30 > degrees C or more to cold fuel within an hour or two. That would expand 10 > gallons to about 10.3 gallons, so if you've only burned a gallon or two in > that time it could appear as a noticable increase in fuel efficiency. If > there is less fuel in the tank, the same amount of heat will warm the fuel > faster. > > Maybe the fuel guage reads slightly higher as the passenger compartment > warms up? > (hey Mike - it has been a while since we've been in the same thread. How's things?) That expansion of gasoline is kind of interesting, if you think about it: It really means that fuel should be sold by volume and temperature if things were fair, huh? There really should be an adjustment of price at the pump, taking tank and outside temperature into account - a multiplier of the gas price. We know the oil companies are not dishonest, (can't get my eyeballs to roll down for some reason now :) but let's suppose they are totally evil, it would be in their interest to heat the fuel before they sell it to us. If they heat it just one degree above ambient, it would be a totally legal way of them making giving you 0.999 gallons for the price of 1 gallon. So in winter you're really getting ripped of a little, the buried gas station tank being warmer than your car tank. By the time you've been driving in the cold for a while, that gallon is really not a gallon anymore. Just a thought - maybe a silly one but it does make me go "mmmmmmmmmmm..." You guys better be happy I am on the right side of evil here :) Remco |
Re: Gas Tank Level Theory
"Michael Pardee" <michaeltnull@cybertrails.com> wrote
snip > It seems plausible. The volumetric coefficient of expansion of gasoline is > about 0.1% per degree C (http://tinyurl.com/bpp2k) and the constant > circulation of the fuel through the engine compartment (through the fuel > pressure regulator) and warming by the in-tank pump could plausibly add 30 > degrees C or more to cold fuel within an hour or two. That would expand 10 > gallons to about 10.3 gallons, so if you've only burned a gallon or two in > that time it could appear as a noticable increase in fuel efficiency. Thanks for the numbers. They are not as impressive as I would have hoped, given the difference I seem to detect. I believe I see around 30-50 miles difference to get from full to a half-tank, from summer to winter. The roughly 0.3 gallons might account for maybe 12 miles of this. (My 91 Civic gets about 40 mpg and holds about 11+ gallons, though these days I rarely let the car empty more than about 9.5 gallons between fillups.) I am also not sure how or whether the non-uniform shape of the tank figures into this. |
Re: Gas Tank Level Theory
Elle wrote:
> "Michael Pardee" <michaeltnull@cybertrails.com> wrote > snip > > It seems plausible. The volumetric coefficient of > expansion of gasoline is > > about 0.1% per degree C (http://tinyurl.com/bpp2k) and the > constant > > circulation of the fuel through the engine compartment > (through the fuel > > pressure regulator) and warming by the in-tank pump could > plausibly add 30 > > degrees C or more to cold fuel within an hour or two. That > would expand 10 > > gallons to about 10.3 gallons, so if you've only burned a > gallon or two in > > that time it could appear as a noticable increase in fuel > efficiency. > > Thanks for the numbers. They are not as impressive as I > would have hoped, given the difference I seem to detect. I > believe I see around 30-50 miles difference to get from full > to a half-tank, from summer to winter. The roughly 0.3 > gallons might account for maybe 12 miles of this. (My 91 > Civic gets about 40 mpg and holds about 11+ gallons, though > these days I rarely let the car empty more than about 9.5 > gallons between fillups.) > > I am also not sure how or whether the non-uniform shape of > the tank figures into this. I think it is a very interesting question you've asked. This is a great discussion. One would imagine that all these errors accumulate (expansion, fuel indicator) so maybe with all errors added in you'll see that 30-50 miles discrepancy. The only way to know for sure is to gather imperical, recording mileage and gallons because you don't know if you can trust your gauge. It would at least eliminate it as a variable and possibly accuse it. Non-uniformity of the tank just tends to make the error worse as they don't linearize the indicator very well. Of course, the tank shape is the same in winter/summer. The way they approximate the linearity probably walks with temperature, so there's most likely another small error. Of course - not to give anyone mental whiplash - it could also be that the car just runs richer in winter for whatever reason.. |
Re: Gas Tank Level Theory
Waiving the right to remain silent, "Elle"
<honda.lioness@earthlink.net> said: > Thanks for the numbers. They are not as impressive as I > would have hoped, given the difference I seem to detect. I > believe I see around 30-50 miles difference to get from full > to a half-tank, from summer to winter. The roughly 0.3 > gallons might account for maybe 12 miles of this. (My 91 > Civic gets about 40 mpg and holds about 11+ gallons, though > these days I rarely let the car empty more than about 9.5 > gallons between fillups.) In summer and winter, you are buying different blends of gasoline. That cold easily accont for the change in mileage. Also... You should never use the fuel gauge to calculate mileage. Fill up the tank and zero your trip odometer. Drive until you have about 1/4 tank remaining. Fill up, then calculate mileage based on actual miles driven. Do this several times and take an average. -- Larry J. - Remove spamtrap in ALLCAPS to e-mail "I've come here to enjoy nature. Don't talk to me about the environment!" - 'Denny Crane' |
Re: Gas Tank Level Theory
"Remco" <whybcuz@yahoo.com> wrote
snip > One would imagine that all these errors accumulate (expansion, fuel > indicator) so maybe with all errors added in you'll see that 30-50 > miles discrepancy. I agree, so far. > The only way to know for sure is to gather imperical, recording mileage > and gallons because you don't know if you can trust your gauge. It > would at least eliminate it as a variable and possibly 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. > Non-uniformity of the tank just tends to make the error worse as they > don't linearize the indicator very well. Of course, the tank shape is > the same in winter/summer. The way they approximate the linearity > probably walks with temperature, so there's most likely another small > error. > > Of course - not to give anyone mental whiplash - it could also be that > the car just runs richer in winter for whatever reason.. 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. |
Re: Gas Tank Level Theory
"Larry J." <usenet2@DE.LETE.THISljvideo.com> wrote
> Waiving the right to remain silent, "Elle" > <honda.lioness@earthlink.net> said: > > > Thanks for the numbers. They are not as impressive as I > > would have hoped, given the difference I seem to detect. I > > believe I see around 30-50 miles difference to get from full > > to a half-tank, from summer to winter. The roughly 0.3 > > gallons might account for maybe 12 miles of this. (My 91 > > Civic gets about 40 mpg and holds about 11+ gallons, though > > these days I rarely let the car empty more than about 9.5 > > gallons between fillups.) > > In summer and winter, you are buying different blends of gasoline. > That cold easily accont for the change in mileage. Not in my neck of the woods. In some parts of the country, yes, there is a significant difference in gasoline "blends." > Also... You should never use the fuel gauge to calculate mileage. Oy. We're having a miscommunication. > Fill up the tank and zero your trip odometer. Drive until you have > about 1/4 tank remaining. Fill up, then calculate mileage based on > actual miles driven. Do this several times and take an average. That's exactly what I do. |
Re: Gas Tank Level Theory
Elle wrote:
> Oy. > > We're having a miscommunication. > >> Fill up the tank and zero your trip odometer. Drive until > you have >> about 1/4 tank remaining. Fill up, then calculate mileage > based on >> actual miles driven. Do this several times and take an > average. > > That's exactly what I do. 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?) |
Re: Gas Tank Level Theory
Waiving the right to remain silent, SoCalMike
<Mikein562athotmail@hotmail.com> said: > Elle wrote: >> Oy. >> >> We're having a miscommunication. >> >>> Fill up the tank and zero your trip odometer. Drive until you >>> have about 1/4 tank remaining. Fill up, then calculate >>> mileage based on actual miles driven. Do this several times >>> and take an average. >> >> That's exactly what I do. > > 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?) So, how many gallons did you use for 285 miles..? -- Larry J. - Remove spamtrap in ALLCAPS to e-mail "I've come here to enjoy nature. Don't talk to me about the environment!" - 'Denny Crane' |
Re: Gas Tank Level Theory
Larry J. wrote:
> Waiving the right to remain silent, SoCalMike > <Mikein562athotmail@hotmail.com> said: > > > Elle wrote: > >> Oy. > >> > >> We're having a miscommunication. > >> > >>> Fill up the tank and zero your trip odometer. Drive until you > >>> have about 1/4 tank remaining. Fill up, then calculate > >>> mileage based on actual miles driven. Do this several times > >>> and take an average. > >> > >> That's exactly what I do. > > > > 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?) > > So, how many gallons did you use for 285 miles..? > Exactly - that's the interesting part. |
Re: Gas Tank Level Theory
Remco wrote:
> Larry J. wrote: >> Waiving the right to remain silent, SoCalMike >> <Mikein562athotmail@hotmail.com> said: >> >>> Elle wrote: >>>> Oy. >>>> >>>> We're having a miscommunication. >>>> >>>>> Fill up the tank and zero your trip odometer. Drive until you >>>>> have about 1/4 tank remaining. Fill up, then calculate >>>>> mileage based on actual miles driven. Do this several times >>>>> and take an average. >>>> That's exactly what I do. >>> 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?) >> So, how many gallons did you use for 285 miles..? >> > > Exactly - that's the interesting part. > 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! |
Re: Gas Tank Level Theory
| 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 <2.2 litre, even a F22A's *'s twin pipes are short. Result is lower though adequate torque @ low rpm ( as during buyers' test drives ), but very low ( <½ as much ) torque & mpg @ high ( >3000 ) rpm, this inadequacy expands with rpm. http://circletrack.com/techarticles/73598 In 6-02 I saw a new Civic vtec 1.6 litre engine with very short * : a waste of vtec ( no way is torque / mpg esp @ high rpm maximised ). www.turborick.com/gsxr1127/gasoline.html para 10.2(1) indicates how bad a civic's * is. Many car makers ( incl Nissan in Sunny 130Y, Hyundai in Sonata 2.4, Proton in Waja 1.8 ) save on *, because 99.99% buyers don't test drive on highways, or know / experienced a difference between short & long branch *. My F20A had crude carbon-core cables made by Sumitomo, efficiency was low ( even by 1990 std ) : longest cable has 12.7k ohm, this is why honda prescribes just 1mm plug gaps. www.magnecor.com/magnecor1/truth.htm I've changed my F20A's spark cables 4x, present set ( German cables ) has just 0.2 ohm/ ft : when warm & w-o load, my F20A can idle @ just 600 rpm, with load ( gear & brake engaged ) then 550 rpm ( without shaking / stalling ). Plug gaps are 2mm. All these are impossible with crude carbon-core cables, this is why honda prescribes 770±50 i.e. minimum 720rpm. How low can your original spec engine ( with crude carbon-core cables ) likewise idle @ ? Carbon can absorb RFI, but cannot conduct as well as metal : high efficiency cables makers coil metal wires around carbon cores, then use these coiled wires to conduct : spark size Ø expands from ½ to 3 mm, 10x brighter, colour turns fr deep to bright blue, 5x as loud.( in open air ). @ high rpm, any engine ( incl yours ) with 1 small coil & crude carbon- core cables will have very small sparks, low torque & loud exhaust noise, this inadequacy expands with rpm. |
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