Better Fuel Mileage with a Full Tank?
09-03-2008, 07:23 PM
#1
Launching!
Thread Starter
iTrader: (1)
Join Date: Oct 2004
Posts: 288
Likes: 0
Received 0 Likes
on
0 Posts
Better Fuel Mileage with a Full Tank? I think for the most part, most of us would agree that the fuel gauges in our cars seem to drop a lot faster below 1/2 or so then they do from full to half. I know the concensus was always that its just the calibration of the gauge and everything, which it very well may be but it seems like everyone I talk to, know matter what kind of car it does the same thing.
Well my dad has been a automotive and heavy equipment technician his whole life and gets invited to these clinics people put on about certain stuff. Well anyways he went to one about fuels and everthing and he was just telling me little tidbits about what it was all about and something he said kind of caught my attention. I guess the person that was putting on this clinic said that cars will get better fuel mileage when above 1/2 tank. Im sure ths only goes for new vehicles or certain vehicles but I guess his reasoning was that the manufacturers dont want there to be a lack a fuel and burn the engine down due to a lean condition. So say the fuel happens to be sloshing around in the tank and the pump cant pick it up and there be a lack of fuel. So they have it programmed that when the gauge starts getting lower the ecm starts to richen the mixture to help prevent this from happening. And I have to be honest I have done some checking and it seems if I fill up before a 1/2 my mileage always seems to be worse then when I run it down to a 1/4 or lower.
So I was just kind of curious as to what you guys thought...I am not saying its true or anything I was just curiouse cause I know mine drops faster below half then above half.
Sorry for the long post guys, I didnt know how explain it in any less words.
Well my dad has been a automotive and heavy equipment technician his whole life and gets invited to these clinics people put on about certain stuff. Well anyways he went to one about fuels and everthing and he was just telling me little tidbits about what it was all about and something he said kind of caught my attention. I guess the person that was putting on this clinic said that cars will get better fuel mileage when above 1/2 tank. Im sure ths only goes for new vehicles or certain vehicles but I guess his reasoning was that the manufacturers dont want there to be a lack a fuel and burn the engine down due to a lean condition. So say the fuel happens to be sloshing around in the tank and the pump cant pick it up and there be a lack of fuel. So they have it programmed that when the gauge starts getting lower the ecm starts to richen the mixture to help prevent this from happening. And I have to be honest I have done some checking and it seems if I fill up before a 1/2 my mileage always seems to be worse then when I run it down to a 1/4 or lower.
So I was just kind of curious as to what you guys thought...I am not saying its true or anything I was just curiouse cause I know mine drops faster below half then above half.
Sorry for the long post guys, I didnt know how explain it in any less words.
09-03-2008, 07:53 PM
#5
Launching!
Thread Starter
iTrader: (1)
Join Date: Oct 2004
Posts: 288
Likes: 0
Received 0 Likes
on
0 Posts
Yeah I'm sure there are other cars out there like that. I dont know where he got his info from I just thought I'd see what you other people thought. At first I thought it was total BS but I have to admit it kind of got me thinking when I thought of the gauge in my T/A.
09-03-2008, 07:56 PM
#6
TECH Fanatic
Join Date: Jan 2007
Location: LITH, IL.
Posts: 1,029
Likes: 0
Received 0 Likes
on
0 Posts
No.
Here is a simplified cross section of your gas tank: Smaller at the bottom than at the top.
\ -------- /
\ ------ /
\ -----/
\ ---/
____
consider your fuel gauge sender to be a stick right down the middle of it. When it reads half-full (or empty if you are of the pesimist persuasion) you would have gone through 2/3 of the fuel in it if it were a perfect triangle. It is not so exagerated, so you have not gone through the full 2/3 amount, but the principle is the same. The tank is bigger at the top. Add in GM's perchant for calibrating it to read full for a few gallons before the gauge moves off full and there you have it. The less weight you have in the car, the better mileage you will get, all else being equal. So you get the best mileage with the tank as close to empty as possible. Not good for cooling your fuel pump, so it is not recommended.
Here is a simplified cross section of your gas tank: Smaller at the bottom than at the top.
\ -------- /
\ ------ /
\ -----/
\ ---/
____
consider your fuel gauge sender to be a stick right down the middle of it. When it reads half-full (or empty if you are of the pesimist persuasion) you would have gone through 2/3 of the fuel in it if it were a perfect triangle. It is not so exagerated, so you have not gone through the full 2/3 amount, but the principle is the same. The tank is bigger at the top. Add in GM's perchant for calibrating it to read full for a few gallons before the gauge moves off full and there you have it. The less weight you have in the car, the better mileage you will get, all else being equal. So you get the best mileage with the tank as close to empty as possible. Not good for cooling your fuel pump, so it is not recommended.
09-03-2008, 09:18 PM
#7
No.
Here is a simplified cross section of your gas tank: Smaller at the bottom than at the top.
\ -------- /
\ ------ /
\ -----/
\ ---/
____
consider your fuel gauge sender to be a stick right down the middle of it. When it reads half-full (or empty if you are of the pesimist persuasion) you would have gone through 2/3 of the fuel in it if it were a perfect triangle. It is not so exagerated, so you have not gone through the full 2/3 amount, but the principle is the same. The tank is bigger at the top. Add in GM's perchant for calibrating it to read full for a few gallons before the gauge moves off full and there you have it. The less weight you have in the car, the better mileage you will get, all else being equal. So you get the best mileage with the tank as close to empty as possible. Not good for cooling your fuel pump, so it is not recommended.
Here is a simplified cross section of your gas tank: Smaller at the bottom than at the top.
\ -------- /
\ ------ /
\ -----/
\ ---/
____
consider your fuel gauge sender to be a stick right down the middle of it. When it reads half-full (or empty if you are of the pesimist persuasion) you would have gone through 2/3 of the fuel in it if it were a perfect triangle. It is not so exagerated, so you have not gone through the full 2/3 amount, but the principle is the same. The tank is bigger at the top. Add in GM's perchant for calibrating it to read full for a few gallons before the gauge moves off full and there you have it. The less weight you have in the car, the better mileage you will get, all else being equal. So you get the best mileage with the tank as close to empty as possible. Not good for cooling your fuel pump, so it is not recommended.
Trending Topics
09-03-2008, 10:49 PM
#8
TECH Fanatic
Your fuel pump does not know how much gas is left in the tank. The PCM doesn't really care either until the supply stops. The real answer is that the gas gauges in these cars just suck.
My '97 used to run forever on the top of the tank. When the needle dropped to 1/2 tank you had better look for a gas station. The later years (I had a '01, and now '02) seemed to work better. But the middle range o the gauge still falls too fast and the top and bottom readings seem to hold longer. We just aren't getting an acurate reading of what is in the tank.
My '97 used to run forever on the top of the tank. When the needle dropped to 1/2 tank you had better look for a gas station. The later years (I had a '01, and now '02) seemed to work better. But the middle range o the gauge still falls too fast and the top and bottom readings seem to hold longer. We just aren't getting an acurate reading of what is in the tank.
09-04-2008, 11:19 AM
#10
Registered User
Join Date: Sep 2008
Posts: 3
Likes: 0
Received 0 Likes
on
0 Posts
No.
Here is a simplified cross section of your gas tank: Smaller at the bottom than at the top.
\ -------- /
\ ------ /
\ -----/
\ ---/
____
consider your fuel gauge sender to be a stick right down the middle of it. When it reads half-full (or empty if you are of the pesimist persuasion) you would have gone through 2/3 of the fuel in it if it were a perfect triangle. It is not so exagerated, so you have not gone through the full 2/3 amount, but the principle is the same. The tank is bigger at the top. Add in GM's perchant for calibrating it to read full for a few gallons before the gauge moves off full and there you have it. The less weight you have in the car, the better mileage you will get, all else being equal. So you get the best mileage with the tank as close to empty as possible. Not good for cooling your fuel pump, so it is not recommended.
Here is a simplified cross section of your gas tank: Smaller at the bottom than at the top.
\ -------- /
\ ------ /
\ -----/
\ ---/
____
consider your fuel gauge sender to be a stick right down the middle of it. When it reads half-full (or empty if you are of the pesimist persuasion) you would have gone through 2/3 of the fuel in it if it were a perfect triangle. It is not so exagerated, so you have not gone through the full 2/3 amount, but the principle is the same. The tank is bigger at the top. Add in GM's perchant for calibrating it to read full for a few gallons before the gauge moves off full and there you have it. The less weight you have in the car, the better mileage you will get, all else being equal. So you get the best mileage with the tank as close to empty as possible. Not good for cooling your fuel pump, so it is not recommended.
09-04-2008, 01:03 PM
#12
Launching!
Thread Starter
iTrader: (1)
Join Date: Oct 2004
Posts: 288
Likes: 0
Received 0 Likes
on
0 Posts
So I guess MOST cars have the same design of a tank and get smaller at the bottom. Some of the tanks I have had down personally to repace fuel pumps and such are actually narrower at the top...
09-04-2008, 02:36 PM
#15
Launching!
Join Date: Dec 2006
Location: Hoosier Daddy....
Posts: 228
Likes: 0
Received 0 Likes
on
0 Posts
No.
Here is a simplified cross section of your gas tank: Smaller at the bottom than at the top.
\ -------- /
\ ------ /
\ -----/
\ ---/
____
consider your fuel gauge sender to be a stick right down the middle of it. When it reads half-full (or empty if you are of the pesimist persuasion) you would have gone through 2/3 of the fuel in it if it were a perfect triangle. It is not so exagerated, so you have not gone through the full 2/3 amount, but the principle is the same. The tank is bigger at the top. Add in GM's perchant for calibrating it to read full for a few gallons before the gauge moves off full and there you have it. The less weight you have in the car, the better mileage you will get, all else being equal. So you get the best mileage with the tank as close to empty as possible. Not good for cooling your fuel pump, so it is not recommended.
Here is a simplified cross section of your gas tank: Smaller at the bottom than at the top.
\ -------- /
\ ------ /
\ -----/
\ ---/
____
consider your fuel gauge sender to be a stick right down the middle of it. When it reads half-full (or empty if you are of the pesimist persuasion) you would have gone through 2/3 of the fuel in it if it were a perfect triangle. It is not so exagerated, so you have not gone through the full 2/3 amount, but the principle is the same. The tank is bigger at the top. Add in GM's perchant for calibrating it to read full for a few gallons before the gauge moves off full and there you have it. The less weight you have in the car, the better mileage you will get, all else being equal. So you get the best mileage with the tank as close to empty as possible. Not good for cooling your fuel pump, so it is not recommended.
Sounds reasonable to me.
With my 72 Cutlass, when I fill it up, it takes forever to get from the full mark to the 3/4 mark. Then it won't waste any time getting from 3/4 to 1/4. Then forever from 1/4 to empty. But, I usually fill it at 1/4.
Also, it has a relatively flat bottomed gas tank, no ECM, a carburetor, and a mechanical fuel pump. I have an 85 Chevy truck as a winter beater. It's fuel gauge acts the same way. Dual fuel tanks, and the sending units act the same.
I'd say the GM fuel gauges are and have been funky for some years.
09-04-2008, 03:03 PM
#17
TECH Enthusiast
Join Date: Aug 2006
Location: In your sisters panties
Posts: 623
Likes: 0
Received 0 Likes
on
0 Posts
09-04-2008, 04:27 PM
#18
TECH Fanatic
Join Date: Apr 2008
Location: Shillington PA
Posts: 1,775
Likes: 0
Received 0 Likes
on
0 Posts
i have been getting that a lot lately, 220 at the most, and im not on it *too* much lol, i think its running pig rich since i put a cutout on it. (no i dont drive any different than i did before, yea i like the sound, but i liked the sound b4 the cutout)
09-04-2008, 10:09 PM
#19
TECH Fanatic
iTrader: (2)
Join Date: Nov 2007
Location: Newport, RI
Posts: 1,406
Likes: 0
Received 0 Likes
on
0 Posts
I read an article in Car and Driver years ago about this. One of the reasons that the guage drops slower from full to 1/2 is so people think they're getting better mileage.
If you fill it up and have gone 40 miles and the needle is still on full, you think "wow, this car gets great mileage!"
Since most people (at least maybe at the time they started doing this) don't run it past 1/4, it was a way to fool people into thinking they were getting better mileage than they actually did.
If you fill it up and have gone 40 miles and the needle is still on full, you think "wow, this car gets great mileage!"
Since most people (at least maybe at the time they started doing this) don't run it past 1/4, it was a way to fool people into thinking they were getting better mileage than they actually did.
09-04-2008, 10:54 PM
#20
I've filled up at different points of the gas gauge and have come to figure out just where everything stands.
Mine's a 98 so this really doesn't apply to all or even more than my car really, but here's my experience. 15.5 gallon tank
3/4 mark is actually a little more than a third used close to 40% really. I've managed to get around 6 gallons in the tank.
1/2 is almost 9 gallons used.
1/4 means 11 gallons used. That last 1/4 goes by quick on my car.
Red zone usually has 2-3 gallons left in tank. I've driven at 70mph for a good hour when it touched red and found when I filled it I could only get 14-14.5 gallons in. Never have come close to putting 15 in.
It's completely f-ed at the moment the way I see it. I simply consider how much I've driven and what kind of driving I've done, be it highway or city and judge accordingly. Combined 50/50 I will see 250miles at best, all city will be closer to 200, and all highway can hit 350+ miles.
I miss the stock days of 400 highway and 300 combined...
Mine's a 98 so this really doesn't apply to all or even more than my car really, but here's my experience. 15.5 gallon tank
3/4 mark is actually a little more than a third used close to 40% really. I've managed to get around 6 gallons in the tank.
1/2 is almost 9 gallons used.
1/4 means 11 gallons used. That last 1/4 goes by quick on my car.
Red zone usually has 2-3 gallons left in tank. I've driven at 70mph for a good hour when it touched red and found when I filled it I could only get 14-14.5 gallons in. Never have come close to putting 15 in.
It's completely f-ed at the moment the way I see it. I simply consider how much I've driven and what kind of driving I've done, be it highway or city and judge accordingly. Combined 50/50 I will see 250miles at best, all city will be closer to 200, and all highway can hit 350+ miles.
I miss the stock days of 400 highway and 300 combined...