over the last 5 days i had to take 2 road trips, both about 4 hours roundtrip. the first one was me alone, windows down, 80% of it at 70-75mph. the second trip was 2 people, windows up, ac on, 85-90% at 70-75. i averaged 24.4 mpg on the first trip, second trip was 24.3.

now the strange part... both times i got over 200 miles on the first half of the tank and only around 150 on the second half.i really can't figure out what happened. i have made the same trips on both of my other cars and they were both normal, meaning i got just as many miles from the first half as the second half of the tank. what gives?

 

I think it's because of the 1 or 2 gallons for the reserve. Mine does the same thing.
Another one of Jag's little quirks!

 

This seems to happen to an extent in all of the cars I have owned. I agree...probably just the engineers trying to make sure you don't run out of gas. My other car is a Jeep. With that I get 175 on the first half and 125 on the second half.

 

The gas tank is probably shaped like a V so it will seem to last longer before half a tank then it will quickly run out once you get past the half way mark. Is your car throwing any codes? Did you clean the injectors? Oil changes up to date? Tires properly inflated? New filters? All these variables effect your mpg.

 

think a lot depends on how high up the filler neck you fill the tank as the gauge cannot read this 'extra' fuel.

 

As per rivs.........they covered this in top gear when they drove the Audi A8 from London - Edinburgh - London on one tank of gas. A total of 800 miles.
He did mention about the "extra" fuel in the neck of the tank that is essentially unaccounted for. Obviously you can only use this once

You're always gonna get more outta the first "half" tank than you will the second "half"


JC

 

When you filled up the first time you probably "topped" off the gas....meaning you probably squeeze in more fuel than you did on your second fill up......common problem....

 

nope racer, i never squeeze any extra in. when it stops, it stops. no need to risk having expensive gas fall out all over my cars. i guess you missed the part where i said the milage was .10mpg difference between the 2 tanks. i was talking about the actual milage.

rivs - i can understand there is a bit of extra in the fill tube, but 2+ gallons worth? that idea doesn't fly with me.

peewee - yes those things are all checked regularly, but there is no way they could have been a factor considering i did the first trip on thrusday/friday and the second trip saturday/sunday. just not enough time for any of those items to change the milage that much.

i guess i will chalk it up to the float needle being somehow slightly off on it's calibration. it did show the exact same results on both tanks, so it is reading correctly, just not completely correctly.

 

ah....well than i guess it's just a plain ol mystery than...

 

Its pretty good how there isnt much difference between having ure windows down or using air conditioning.

 

You talkin bout mpg wise 04?

JC

 

Yeah. sorry i wasnt more specific

 

I's sure I heard somewhere, its about 5% of your fuel economy!
Just from memory.

JC

 

They did a test on mythbusters and the suv with the windows open actually lapped around the track a couple of more times as the one with ac on ran out of gas...although the computer information they gathered said that the actual result should be that windows up and a/c on in mainly highway is actually better than windows down...those results were concluded by taking in the air mixture and all that stuff into their computers but on the track with identical suvs the one without a/c on kept running...I'll keep using my a/c when it is over 80 degrees though so either way it doesn't matter...gotta keep the baby from sweating back there!

Nineball-I've noticed this with both of my vehicles and vehicles in the past...I just figured that it isn't an exact science and would rather just keep track of total mileage...The jag gets more mpg the first half and less the second half like you...

 

There's more in the first "half" tank taking into account the filler pipe. You'll always get "more" out the first half so to speak. At least thats always been the way in any car I've had.

JC

 

Thats what I figured don't really look into it too much though.,,

 

I remember reading this thread a long while back.

I was reminded of it the other day when my X ran out of gas on the highway. I've coasted on fumes plenty of times before in the past, but always with a conscious effort to see how far a car could go before the tank is truly empty (and I've never actually pushed it past the breaking-point).

I don't know what happened Monday morning, but I never even noticed that the orange light was on signalling to me that my tank had been empty (apparently for some time). I was smack in between two exits about 3 miles apart from one another when the throttle just gave-out, and then the 'check-engine' type lights turned on and I coasted to a stop. LOL!

Oh man. Note to Self: "When the gas-gauge is pointing to the last tick-line next to the E, it really IS empty."

I hate Mondays.

 

LOL!!!

Thread from the dead...almost a year to the date happi!

 

NORMAL
If your not content with this answer you could always have car scanned for fuel level sensor faults
If there are no codes then there are no faults
NORMAL