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Discussion Starter #1
I just had my first fill up yesterday, and I got really confused. I know the official tank size is 16.6 gallons, but I always "top off" the car whenever I'm at the pump. I don't want to be coming back to a gas station any earlier than I have to! So the "auto flow" shut off at 15.5 gallons, but I was curious to see how much more it could take. So I'm carefully goosing the pump handle, waiting for what I expected from my previous car: the gas would eventually bubble up a little bit at the top and even be visible there, showing that not only the tank but the whole line going down to the tank was full.

So I kept going...and going... and going. It never bubbled up! I looked back at the meter and was shocked to see I'd put in 17.1 gallons of fuel! I stopped there, disappointed and a bit confused as to what was going on. I got on my hands and knees and looked under the vehicle to see if there was a horrible spreading pool of leaking gasoline or something. I didn't see any, but what the heck?

How on earth was I able to fit over half a gallon more than the tank is even rated for into the car??
 

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The tank is designed to be filled at a minimum gal/min rate and to cause the pump to shut off when capacity is reached. The additional space in the tank is to allow for expansion of cool gas pumped into a warm environment. Overfilling such as you describe will damage the evap canister. I would take my car out on the freeway and hit every exit and when re-entering, accelerate briskly to burn up the excess gasoline. You have overfilled your car by at least 1.5 gallons.

On long road trips, I would fill my previous car ('08 Matrix) and top off up to another gallon. By the time the gas would have expanded, there would be room in the tank from driving freeway speeds.

artosa
 

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I do Costco gas, where they have signs to not top off. Most people obey them, in and out, let the next guy get his gas. Some pain in the butts, not many, stand there goosing the pump for every drop they can get keeping other people waiting even longer. GRRRR!!!!
 

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I have never "topped off" any of my subaru gas tanks. As you saw what happened. I usually get around 14 gallons when I fill up. Just fill, click and go.
 

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We fill up when the light comes on and stop at the second click. The most it's taken is 15.6 gallons, which is about right, based on the 16.6 gallon capacity.
 

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I used to max out my VW with 4 L past the click. Never had a problem after 10 years of doing so. However, because I’m tracking my XV fuel, I always stop at the first click. My fill ups are usually 43-46L so that means I usually have about 17-20L left.

Ref: “I don't want to be coming back to a gas station any earlier than I have to!”

Don’t wait on long before filling up. Gasoline is a fuel pump coolant and over time you could suck up any sludge that may be in the tank. I always top up around 1/4 or thereabouts.
 

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I used to add a bit after the pump stopped in the past, not allot but some, I know my F250 if I do the gauge will read 1/2 for about 20 miles before it nudges up to Full, but not anymore...worse case is for some unknown psychological reason if it's say $32.77 I will click to $32.80 (for example) but no more than about a few cents to make it even.

Don't want to brunt the cost of a evap canister...
 

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I used to add a bit after the pump stopped in the past, not allot but some, I know my F250 if I do the gauge will read 1/2 for about 20 miles before it nudges up to Full, but not anymore...worse case is for some unknown psychological reason if it's say $32.77 I will click to $32.80 (for example) but no more than about a few cents to make it even.

Don't want to brunt the cost of a evap canister...
I always used to do the same, makes it easier doing the checkbook. But now that the bank manages the checking, and all other accounts, and I don't have to worry about entering odd numbers, I just stop when it stops.
 

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I always used to do the same, makes it easier doing the checkbook. But now that the bank manages the checking, and all other accounts, and I don't have to worry about entering odd numbers, I just stop when it stops.
The petrol station nearest to where I grew up had a very strict owner. If you tried to get the pump to exactly, say, ten British Pounds but you went 1/2p over, he would make you pay the 1/2p (less than once red cent). If you didn't have change you had to break another tenner and he would give you nine Pounds, 99 and 1/2p in change. I stopped going there... actually, he told me he wouldn't serve me any more because he thought I drove in and out of his petrol station too recklessly in my Spitfire. I was 17... :D
 

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Discussion Starter #11 (Edited)
The tank is designed to be filled at a minimum gal/min rate and to cause the pump to shut off when capacity is reached. The additional space in the tank is to allow for expansion of cool gas pumped into a warm environment. Overfilling such as you describe will damage the evap canister. I would take my car out on the freeway and hit every exit and when re-entering, accelerate briskly to burn up the excess gasoline. You have overfilled your car by at least 1.5 gallons.

On long road trips, I would fill my previous car ('08 Matrix) and top off up to another gallon. By the time the gas would have expanded, there would be room in the tank from driving freeway speeds.

artosa
Thank you for the insight everyone, and artosa in particular. I'm still confused - so does that mean that the tank is not "actually" 16.6 gallons, and it is actually larger to make room for these gases? When I looked under the car and saw there was no puddle of spreading gasoline, I was wondering where the heck the gasoline even went!

I use Fuelio to track my MPG's but Fuelio bases its calculations off of how many gallons you put in at a fill-up, vs what the rated capacity of the tank is. Which is why I always "top off" the car (and no, I don't do it anywhere there is any kind of line of vehicles waiting to use the pumps - I live in a very small city) - I do it so that I can tell Fuelio accurately "here is how many gallons it took to reach Full - actually full, not just when the pump shuts off".

If I don't top off the car, how can I accurately measure my MPGs?
 

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If I don't top off the car, how can I accurately measure my MPGs?
Just be consistent. I wait until it clicks off, then try again until the next click. Our fill up quantities are extremely consistent, ranging from 14.9 gallons to 15.6 gallons. And that's due to the difference in miles between when the idiot light comes on and when we actually fill up.
 

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When I fill up, the last couple of gallons are at the slowest setting on the pump handle, then manually slowing the pump even more till it clicks. Haven't added more than two/tenths gal. after clicking off because the tank seems full. Am trying to use the same station/pump when I'm able. Not positive, but if car is slightly downhill it will take more gas.

artosa
 

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Thank you for the insight everyone, and artosa in particular. I'm still confused - so does that mean that the tank is not "actually" 16.6 gallons, and it is actually larger to make room for these gases? When I looked under the car and saw there was no puddle of spreading gasoline, I was wondering where the heck the gasoline even went!

I use Fuelio to track my MPG's but Fuelio bases its calculations off of how many gallons you put in at a fill-up, vs what the rated capacity of the tank is. Which is why I always "top off" the car (and no, I don't do it anywhere there is any kind of line of vehicles waiting to use the pumps - I live in a very small city) - I do it so that I can tell Fuelio accurately "here is how many gallons it took to reach Full - actually full, not just when the pump shuts off".

If I don't top off the car, how can I accurately measure my MPGs?
No wonder I didn't like Fuelio when I tried it. That does not sound very accurate at all. If you traveled so many miles and used so much gas, dividing by how much you used and how far you went seems to make more sense than basing it on what they consider a full tank (?). Regardless of what size the gas tank is, you used 10 gallons to go 200 miles, therefore you burned 1 gallon for every 20 miles. Who cares what size the tank is and how full you actually got or didn't get it each time? If you go to shutoff every time, that is how much you burned.
 

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The petrol station nearest to where I grew up had a very strict owner. If you tried to get the pump to exactly, say, ten British Pounds but you went 1/2p over, he would make you pay the 1/2p (less than once red cent). If you didn't have change you had to break another tenner and he would give you nine Pounds, 99 and 1/2p in change. I stopped going there... actually, he told me he wouldn't serve me any more because he thought I drove in and out of his petrol station too recklessly in my Spitfire. I was 17... :D
For us Yanks in the audience, would that make him a "yabbo" or a "wanker?" :D
 

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As has already been said, please for everyone’s sake don’t “top off” and just stop when the pump shuts off. It’s bad for the car, bad for the people waiting, and honestly what’s it get you? A few extra miles before you need gas again?
 

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Discussion Starter #18
Duly noted, everyone who has repeatedly told me it's a bad idea to top off your car ;-) I get it. Potentially bad for the car. I really hope I didn't screw something up with the charcoal filter by filling up to 17.1 gallons. I asked my dad what he thought about this, as the saying goes "I learned it from yoooooouuuu!" and asked him if he still "topped up" - he said, of course! It's the only way to track your MPGs! I just warned him, though, that since he also brought a brand new car just last week, a hybrid, perhaps he should consider that there's no website out there saying "go ahead and top off your car." He said he would think about it.

It is kind of amusing though, that so many sites are parroting each other with the same three bullet points. "Bad for your car! Bad for your wallet! Bad for the environment!" and just copying and pasting each other. No new info under the sun, so let's just rehash the same three thoughts over and over again for clicks.
 

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I find no reason to get every drop even on road trips. I get around 450 miles per tank. No matter where you go in the US, it is guaranteed that there will be a gas station every 50-75 miles, even less probably. I may be wrong, but I have circumnavigated the US with my friends because we love road trips. I am speaking only on my experience though.

Sometimes it's good to stretch your legs on long trips and pump some gas and maybe explore the area.
 

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I find no reason to get every drop even on road trips. I get around 450 miles per tank. No matter where you go in the US, it is guaranteed that there will be a gas station every 50-75 miles, even less probably. I may be wrong, but I have circumnavigated the US with my friends because we love road trips. I am speaking only on my experience though.

Sometimes it's good to stretch your legs on long trips and pump some gas and maybe explore the area.
When I'm on a road trip, I try to do a stop every 2 hours. I fill two tanks (caffeine and gas) and drain one tank (;)). I also walk around a little to get the blood flowing. I may skip the fuel fill every other stop depending on where I am and what's available ahead. Across the midwest where there's a stop every 3-5 miles, I will skip it. But when I'm in remote areas with longer distances between gas stations I fill up more often.

I have taken the fuel down to when the warning lamp is on just to see how much it takes to fill from that point. But I typically don't let it get down less than 1/4 tank (as indicated on the gauge) because more gas in the tank keeps the pump cool.

I have also filled past where the pump clicks off just to know how much more it takes to get all the way up the filler neck. Most of the time I just let it go until it clicks off and I'm done. Mostly so there's room for the gas to expand as it warms. I do it even when I'm calculating actual mileage. It doesn't always click off exactly the same every time so I know that my individual tank fills will vary in calculated mileage a little. But an average over 3-4 tanks will be pretty accurate.

It's also important to remember that the entire fuel system has more capacity than the tank. All of the fuel lines from the tank as well as the filler neck can hold a couple of gallons or more (depending on the vehicle). So with a 16.6 gallon tank you can easily get more in the car.
 
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