Last few weeks I have being getting less mileage and today actually ran out of gas, andI had to put my thumb out. I usually rely on trip meter because fuel gauge is not very precise, I thought maybe sitting in sun with not much in tank might cause evaporation but a mate says the problem is fuel expands so you are getting less for the buck. Anybody know if this is right and how much.
thejazzpianoma,
Feb 15, 6:46am
1. Try not to run your car so low on gas, running out and almost running out can actually damage your catalytic converter if you do it enough.
2. Possibly more to do with fuel going up than anything. Admittedly hotter air entering the intake could make a very small difference to economy (more noticeable on an older vehicle).
3. Not sure exactly whats meant by the fuel expanding with heat thing, that seems mumbo jumbo to me.
brucet3,
Feb 15, 7:03am
Do not usually run low, but am 70 k's from a pump it is always a bit of an issue. What is meant as some fuels (airplane or even household gasfor example) are sold by weight not volume because both liquid and gas fuels expand and contract according to temperature, and so a litre at 1 degree centigrade is going to run your motor longer than a litre at 35 centigrade.
thejazzpianoma,
Feb 15, 7:05am
Morrisman, might be able to break out some exact math on this one for us. I would have thought with the tanks being underground (and therfore fairly stable temperature wise) the difference would be negligible.
Its unlikely the fuel temperature in the underground tanks is going to vary much so temperature is unlikely to affect that side of it.
What temperature does affect is air density in a big way. Engines need oxygen so the denser the air the more oxygen is in the cylinder so it can be more powerful. Modern cars will account for high temperatures and lean the mixture as necessary but an older car will not. To achieve the same power you will need to have a larger volume air let into the engine than if the air was dense and fuel is metered off air volume so with hot air you will use more gas.
morrisman1,
Feb 15, 7:13am
some exact math for you jazz, the international standard figures for the atmosphere at sea level are 1013 hPa, 15°C which gives a density of 1.125kg/m^3.
Increasing pressure, for every hPa will increase the density to the effect of descending 30' (10m), the opposite applies for lower pressures
Increasing temperature for every 1°C above standard is equivalent to being 120' higher up (40m) and vice versa so its easy to see that air density is greatly affected by temperature.
Thats why race cars have the intakes in cold spots and why pod filters are rubbish (suck warm air)
Edit: So lets have a scenario: currently it is at Auckland airport 1020 hPa and 22°C. Higher pressure so 0' - (30*7) = -210' (with 7 being the difference between actual and standard) then -210 + (120*7) = 630' density altitude.
Now this may not seem much it can make the difference between a 1000'/min climb in an aircraft and a 700'/min climb. In some places like singapore where its stonking hot and low pressure the performance of any non turbo charged combustion engine is markedly decreased (for the same fuel consumption rate)
gooddealz2,
Feb 15, 10:49am
I can only suggest a move to Dunedin where driving a car must be incredibly cheap based on the s.t weather we;ve had lately.
whynot7,
Feb 15, 11:02am
#7 i started to read that .but my head exploded
stevo2,
Feb 15, 5:14pm
Moorisman1 hit it on the head. Cars run more efficiently at cooler temperatures. Cheers Stevo
poohy99,
Feb 15, 6:01pm
Um, they can produce more power at lower temperatures, efficiency is another story.
morrisman1,
Feb 15, 6:53pm
would someone clean that up please, its starting to smell
rod525,
Feb 15, 6:57pm
Just keep it above a quarter on the gauge and you won't have a problem.
sifty,
Feb 15, 7:57pm
I remember fondly how well the old GSXR would go on cool, foggy mornings. Noticably more power, just a shame you couldn't see where you were going.
intrade,
Feb 15, 9:45pm
you need to fill up early morning i do not know if the underground tanks cool overnight but if they do you would get more fuel as it expands in the heat during the day in your cars tank. other reason could be a faulty meter on fuelpump where you filled. or you did not see that you get less and less fuel for your 20$ due to prices rising . or you got a fuel leek somwhere.
intrade,
Feb 15, 9:47pm
thats to do with moisture in the air its like water injection. works on a similar principal then foog that the engine sucks innn. And cold air contains more oxigen then hot air its why you have a intercooler on a turbocharged vehicle to gain hp by cooling the hot air the charger heated up.
intrade,
Feb 15, 9:51pm
also its not smart to run a car out of fuel. loads of them damage the fuelpump inside the tank when you run em dry for like 30 secounds and they damage and stop working costing 150 to 300$ for pump and sometimes 6h labour to fit inside fuel tanks. loads of $ you could buy fuel with. to name 2 cars Volkswagen passat vr6 and mazda capella 1998
1ollie,
Feb 15, 9:58pm
You say airplane gas is sold by weight! Avgas isint! its sold by the L like normal
richardmayes,
Feb 16, 1:43am
LOL! Maybe the fuel gauge isn't so bad after all!
elect70,
Feb 16, 2:00am
Remember the old days of CNG filled by pressure not volume .Fill up ona cold day & got more in the tank . I eventried pulling a vacumnm on the tank , got a bit more
scoobeey,
Feb 16, 2:04am
true lol
rsr72,
Feb 16, 3:36am
Yes, denser, more into the tank.
socram,
Feb 16, 4:21am
I don't think the temperature change in an insulated underground tank would vary more than a degree or so.
Although my head didn't explode (but I did get the gist), we all know that both cars and humans don't function as well at high altitude where the air is less dense, so a cool foggy morning will produce more power/efficiency or economy - take your pick.
When F1 teams used to travel to high altitude Mexico years ago, well before computerisation, they knew damn well power would be way down on European tracks at sea level.
Keeping your tank level above 1/4 is presumably to try and stop the fuel in the tank heating up and evaporating.Park in a garage or in the shade whenever possible.
pandai,
Feb 16, 5:21am
I am guessing the OP just used their air conditioning a bit more than usual
franko171,
Feb 16, 7:11am
i find i get different milage out of differant brands . yes that is filling to top of tank and useing trip meter.
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