Miles Per Gallon.

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I have a 2002 Town Country 3.8 engine when I check the gas miles after adding say 15 gal of gas the miles are around 17.7 mpg if I run the tank empty and add 17 gal of gas the mpg is 19.0
I dont understand why this happens and I have checked this very closley. I had a Dodge Caravan with the same scenario is there a reason for this it drives me nuts trying to understand why.

Daryl
 
Humm, could be the fact when you run it down on fumes then fill up, you are getting a greater percentage of "fresh" gas, giving you slightly better mpg.
dunno.gif
 
The weight difference isn't causing the change - it is way too small to mean anything.
Possibly your fuel pump is causing the car to run leaner with less fuel in the tank.
 
Is there any chance that the vehicle has an oddly shaped tank that can trap air somewhere? If it did, then an air pocket may prevent complete fill from near empty. The mileage would seem to be better. It would also follow that the next tank would appear to give lower mileage if filled before the "air trap" level.
 
The obvious question is "Is the tank full to the brim each time you fillup, regardless of the volume put in."

There could be some variability in the fillup which could explain some of the difference.

At any rate, you are being a tad anal about this.
 
bobo,

Every gas fill up is done the same way I do not think I am being anal it has been going on for about 5 years in two different vans there has to be a logical answer.

Daryl
 
The weight of 2 gallons of gas is nowhere near enough to cause a difference of 1 mpg. But feel free to prove me wrong.
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Try topping up at, say, 10 gallons and see if you get even worse mileage.
 
Vilan,

It is the same scenario as adding 15 gallons it seems the closer I run the tank to empty the better the gas miles gets as a I stated in the above post this has been going on for the last 5 years and it drives me nuts that I have not been able to solve this issue.
 
ShortBuSX,

You are correct never thought of the weight issue I should have as much as I watch NASCAR and the driver fuel issues thanks.

Daryl
 
2 gallons is about 18 lbs, right? Not enough change due to weight. It's something else. I doubt it's related to the fuel pump function...fuel pumps don't cause lean running conditions, fuel injection/ecu's do that. My guess is that it is something to do with the way the person is filling the tank, causing a variability in the way it is filled.
 
Yeah, hmmm, perhaps it's something to do with the evaporative emissions system or something. Perhaps it doesn't function properly until you get close to empty?
dunno.gif
 
the real question that should be asked is: are you getting these results by CALCULATING the fuel economy, or are you relying on the computer???

That can be a big difference.

JMH
 
JHZR2,

The way I am getting the mpg is drive the van until it is empty fill it up take the gallons of gas used divided into the miles driven gives me the mpg if there is another way please advise
 
If you're calculating this by means of input at the pump, you HAVE to calculate it out over mutliple fills, and preferably use the SAME pump at the same station every time.
 
quote:

Originally posted by dbdeland:
JHZR2,

The way I am getting the mpg is drive the van until it is empty fill it up take the gallons of gas used divided into the miles driven gives me the mpg if there is another way please advise


There are a lot of variables with that method. It's really only good to give you an idea over several fills.

I can change the numbers on my wifes Cherokee simply by letting it fill with the nozzle on the second notch instead of the third. In reality since it's putting fuel in slower I'm getting more fuel before that first shutoff, even if I stop filling at the first time it shuts off using the second or third notch.

I don't have enough patience to put it on the slowest notch and see how much of a difference there is on that one.
 
quote:

Originally posted by dbdeland:
JHZR2,

The way I am getting the mpg is drive the van until it is empty fill it up take the gallons of gas used divided into the miles driven gives me the mpg if there is another way please advise


Nope, filling from empty to full, then dividing that into the number of miles driven is the way to go...

I wasnt sure if you were going by the display that those vans have... that can change for no apparent reason... thus my concern.

JMH
 
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