crazyfool

Hi, im trying to calculate my miles per gallon, but i and stumped becaused i dont know the exact size of the fuel tank, and the reservoir.

currently i am estimating by fill gas all the way to the top, then drive until the empty light comes on.

at that point, i read that the reservoir contains 3 gallons, and that a fuel tank is 17.

so i divided the total from full to empty light by 14.


i am etchy about this as my MPG is lower than expected. does anyone know the exact measurements of the tank and when the reservoir light really comes on? Or what is a better step to measure my MPG.


thanks!

MikePA

1. Fill tank until pump shuts off automatically, record odometer reading
2. Drive until light comes on
3. Fill tank until pump shuts off automatically, record odometer reading

(Second odometer reading - First odometer reading) / Number of gallons at second fill = MPG

No need to know the size of the tank, reserve amount, etc.

fsttyms1

Like said above. You dont need to know the size of the tank. You just need to reset the trip or record your current mileage, fill it up, drive till the light comes on, fill it up. Take the miles driven divided by the amount of gallons put in and that will give you your mileage.

If your doing alot of city driving dont expect the mileage to be good

thisisnotdave

Dont be too upset about getting less than expected numbers, with mixed driving i can barely squeeze 280 from full to light thats roughly 20mpg, but I aint exactly light on the peddle, and what really kills me is the 4 - 5 3 miles trips i make a day when im out at school. Short trips = shite fuel economy.

01tl4tl

You dont need to run it down to the fuel light.
As long as you stop at first auto shutoff of the pump- then drive 3/4 of a tank and refill to the first auto-shut off, miled driven divided by gallons used
example: 300 miles driven and 15 gallons to refill to shut off, = 20 MPG

MikePA

The emptier your tank the less the mpg calculation will be affected by;

Different auto shut offs at the pump
Atypical driving

Also, to the OP, you never want to fill the tank 'all the way to the top' unless you want to run the risk of screwing up the evaporative controls.

01tl4tl

how exactly- does making the tank emptier???- affect the auto shut off ,
which is run by increased back pressure?- my guess-

You can fill to auto stop, run 5 gallons on the freeway cruise and stop-fillup- calculate that mileage, or you can run full tanks.
If you are looking for general number- it takes a few months of driving to establish a mean point applicable to you

All it takes is actual miles driven divided by actual fuel used. Who cares about .3 off in your math

This reminds me of Gen3 owners who have a MPG display on dash- they fill up, then get on the freeway and up to speed before resetting the guage.
All that does is make you feel better as the car still took fuel to get on the freeway and up to speed.

fsttyms1

I agree with Mike
He didnt say it would effect the auto shutoff. But every auto shutoff is different. Not all stop similarly. Plus the more miles driven before fillup the more consistent the result will be. Not to mention give you a better idea of what your weekly mileage or the amount you will get out of the tank

01tl4tl

OK so if we are being extra AR about the mileage gonculations here-
use the same pump at the same station with the same ambient overnight and daytime temps on the same delievery of gas to the station from the tanker.
Thats good for within .003 of an MPG

If you just want to know if you are suddenly getting 15 mph- you dont need a calculator- you need plugs and seafoam~ and check your tire pressure for sure

I will admit to doing serious number cruching and I did run it to the light, seeing if oil brand mattered.
What seemed to affect it most was the use of heavy right foot

MikePA

fsttyms1 explained it well. While all auto shutoffs operate on the same principle, in practice ones at different stations behave differently. It's not theory.

I've put almost 40,000 miles on my car over the past 3 years. Most of the miles are from a 30 mile commute to work. I've averaged 23.8 mpg. (High of 35.6, Low of 14.3) Almost every unusual mpg reading has been when I put less than 5 gallons in the tank. The longer someone drives on a tank of gas, the more likely they are to get a good sample of their typical driving. The difference between 3/4 empty and when the light comes on probably isn't a big deal, though.

01tl4tl

In theory it should be 1 to 1.5 gallons between the 1/4 tank of 17 total (4 of 16 remaining for easy math) and the light at approx 3 gallons
It keeps about 1/2 gallon unusable I think

I only watch for major drop in mileage to indicate problems. A tank goes about 280-300-320-350 and I refill at the light

FirePR2002

I notice differences in efficiency when I use certain brands also. I've seen as much as 8%-10% swing.

FirePR2002

On the numbers ^^, that could account for your midpoint to highpoint or even the middle by about that much. I average 320 miles per tank - filled up with 14.1 gallons (at the first shutoff) today and clocked 318.7 miles since the last fillup. That's 22.6 mpg - not bad for a 50-mile commute round trip in 85% stop-go traffic on I 75.

01tl4tl

my numbers were to indicate worst case scenario hotfoot 280
best case 350---normal for me is 320 and the lights not on yet but not enough gas left for the next trip so fill it up.

Fire- what brand is giving the best result for you? Please share- I want the good gas

VeEzy

im gonna see what i can get out of shell Vpower. people on this board says it makes a differences.


so i pumped today a little prematurely of the warning light. it was at 12.33 gallons to fill up so im guessing the reservoir comes on at 12.5 give or take

i divided 12.5 by 225 and got 18, so im happy.

that is all city driving, but also, that is extremely slow driving (grandma) so i dont know what i should expect.

also i know i get way better effieciency when i just fill half a tank




and is it really bad to fill up the whole tank? ive only been doing it lately to estimate a whole tanks worth. usually i fill half anyways

crazyfool

im gonna see what i can get out of shell Vpower. people on this board says it makes a differences.


so i pumped today a little prematurely of the warning light. it was at 12.33 gallons to fill up so im guessing the reservoir comes on at 12.5 give or take

i divided 12.5 by 225 and got 18, so im happy.

that is all city driving, but also, that is extremely slow driving (grandma) so i dont know what i should expect.

also i know i get way better effieciency when i just fill half a tank




and is it really bad to fill up the whole tank? ive only been doing it lately to estimate a whole tanks worth. usually i fill half anyways

01tl4tl

with the way gas keeps jumping 20 cents every time I get to the station, I carry a full tank I can afford now!
The few pounds you save is not worth it. Gas weighs 6 pounds a gallon

What kind of math do they teach these days? 12 of 17 = what??
- the light comes on and takes 14.1 for most of us
"so i pumped today a little prematurely of the warning light. it was at 12.33 gallons to fill up so im guessing the reservoir comes on at 12.5 give or take"

MikePA

This isn't complicated. You put gas in the tank until the pump automatically shuts off. You do not try and nurse more gas into the tank, i.e., "Fill it to the top" after auto shut off.

myron

iTrader: (4)

fuel tank is 65 liters if that helps anyone

crazyfool

obviously i dont force more than needed.

by saying filling it all the way, i meant by default, the maximum it will take.

01tl4tl

fill the tank to the first auto shut-off. That leaves for for expansion from heat.
Got gas today at 3.79 (gulp) 4 bucks is just 1 more State Primary election away~

rob-2

I get 350-400 miles to a tank mixed and 550+ pure highway. The best I got out of the car, was 620 miles to the tank. This seems to be an odd case though, as I've only been able to get up to 570-590 but never broke the 600 again.

I'll try again this summer.

I use the fill till click and then reset milage method.

FirePR2002

whoa - what gas are you using?

FirePR2002

I use RaceTrac almost exclusively now and my second choice is Shell VPower. After that, I'll drive until I find one of these somewhere or cringe when I have to "settle" for something else. BP is among the worst efficiency I achieve for some reason. And I only use premium.

rob-2

Whatever is cheapest. For the last 6 months I've been burning 87oc.

I've mentioned this before, but on a 2000 mile drive to AZ and back we averaged in the area of 31-32. That's where I got the 620 to the tank. On one fill up it was 38mpg. On the next 34, another 31, one where I let my friend drive 28.

If I get less then 200 miles to the half tank it's been a bad week and I'm driving to hard.

On my most recent fill up, it was 377 miles to 15gals of gas - mixed city/highway. I'm a firm believer in using cruise control all the time.

FirePR2002

Interesting - since I've had the new tranny (about a year now), I'm lucky if I get 100 miles on the top half per the gauge - although I average 320 for the whole tank, i.e. the top half "burns" faster than the bottom half for some reason. This has perplexed from day 1, but since the outcome is the same I haven't investigated it further.

FirePR2002

City / Highway is pretty relative anyway - what I consider city driving in Atlanta, GA is different than someone in Middle of Nowhere, Texas for example. I drive 30 miles each day on the interstate - BUT it is a drag-race for 10-15 feet followed by extreme braking for most of the drivers around me. The best part of my commute is the 10 minute drive past multi-million homes in a residential section of town. MILFs, hotties, and exotic cars everyday.....

crazyfool

...are we driving the same car here? lol

damn thats crazy mileage

rob-2

Funny you mention the new tranny. I got one about 30k ago. I suspect my milage is better now, but I wasn't actually tracking it as much then.

When I really want to get the best milage I keep the rpm's below 2k. In the city it's tough, but on the highway it gets me up to about 75mph

mcflyguy24

Holy shit. I could never be that careful, but it seems like it's saving you tons of $$.
Too heavy footed I guess

crazyfool

i try to keep it under 2K, but no matter how slow i drive, my tranny keeps shifiting at 2500-3000

do you use your manumatic?

also does anyone here think a CAI will improve fuel efficiency over a stock airbox?

mcflyguy24

I use manumatic when I fee like driving fast and when I'm on hilly backroads, I hate grade logic control when I'm taking backroads. I don't want the car to slow down just cos I'm on a hill, or worse yet when I'm taking a downhill corner I hate when the car tries to downshift.
I don't think a CAI will really improve MPG, maybe like 1 MPG better.

But to answer you question, I don't use manumatic to try and improve fuel efficiency.

rob-2

I run in full auto, and only 'play around' in tip mode.

If you want to get better milage start running 87oc. It actually has more BTU's then 91 or 94 oc gas. You'll see an improvement in milage.

Apparently our cars have knock detection and will adjust for the reduce oc rating.