I never top off my tank at the gas station. I regularly have to yell at the gas jockeys who run over and immediately try leaning on the nozzle to shove another $19.00 of gas in after it clicks off. (For those of you who never drove in Jerzey, you're not allowed to pump your own gas, every station is full serve.)

My reasons are very basic. One, the top-off screws up my manual mpg calculating. And two, I read somewhere that there's a vapor sensor around the top of your gas intake that can be damaged if drowned by liquid gasoline. (Pardon my layperson's terms if they're not quite accurate, I'm not a techy guy.)

So am I on the money, or do y'all top off after filling up?

 

I don't top off, but I do slow the fill rate down once I know the tank's getting close to full.

I don't know how much of a difference it makes on the MINI, but I've had other cars where the pump would cut off well before the tank was full if I left the pump on "full-blast" all the way to auto-shutoff.

 

OrEGon is the same way!! have banned my Husband from filling Molly up in OR. We have a Shell Station 1 mile from our house, that is where we usually fill up. I hadn't noticed whether Costco in OR tops off our other car (Durango), but it doesn't have the fuel cap problems I've heard the MINIs have. My Husband or myself will be the only ones to put fuel in Molly!!

 

We get the pleasure of filling up the car ourselves and we don't ever top off the car. I've seen others do that and half the time they end up spilling gas on the car.

 

I don't top off. It is discouraged (if not outright illegal) in California due to air pollution laws. The reasoning is that gas is stored underground and is often cooler than air temp. When it is pumped up into a car, it can warm up in the tank and expand. If the tank was filled to the brim, the expansion would cause some to spill out of the tank and evaporate -- degrading air quality.

It seems that unburned gasoline is worse for air quality than fully combusted gas. Most areas in California require gas pumps to have systems that capture gas fumes while filling a car.

 

I stopped topping off once I started paying with a credit card or with EZPay or Speedpass. There's no point. Who cares if the total is a round number? I'm not getting change anyway.

I also agree with the folks who raised the issue of vapor sensors and with calculating mileage - further reasons not to top off.

Those who live in Jersey: you have my sympathies.

 

Speaking of Jersey, I was getting some gas at home and this really cute girl asked how to pump gas, I actually looked around for the candid camera crew !! then I saw the plates and it all made sense !! She really had no clue how to do it. anyway, I pump till it clicks off, then try to round the number to the next ten cents OCD I guess.

 

I can't say I have any clue why, but my BMW's gas cap says "Do not top off". So, therefore, I don't top off!

Like I said... I don't know why, but when a German company tells me to do something, I tend not to question it.

 

how does it throw off your calculations? Print the receipt, it will tell you how much gas you put into the tank, take the amount of miles driven from the previous fill up and divide it by the total amount of gas you filled up with.

 

I used to work in fuel systems and topping off is only acceptable with the following procedure:

1. To first click have the nozzle fully on
2. 2nd and 3rd clicks, only have the nozzle on the 2nd catch (or ~ 50% on)

STOP THERE! Anything more has a chance of fouling your charcoal cannister, and you won't like the price that comes with replacing it. BTW, you cannot unfoul cannisters once they are saturated with fuel as they are only designed to handle vapor.

 

If you didn't top-off on that previous fill up, then you've put in more gas by topping off at the next fill up. It'll throw off your calculation.

For that matter, I guess the most accurate mileage calculations are from using the same pump at one station since I suppose guns can be calibrated differently to shut off. Also I've been to stations where the flow-rate slowed down when they were busy, so that could throw off a calculation a bit. Nothing's perfect.

 

^^^^^^
If you put in miles traveled and gallons used, the fact that you topped off, should not affect MPG calculations.

 

I used to top off on other cars, it was an OCD thing. Since owning Ferris I haven't though. It's just to difficult to do it right for what little I get out of it.

 

I have to admit, I top off and always have. After reading through this thread though, I'm going to stop.

 

We were told it was not a good idea due to environmental concerns, so no, I don't top off.

 

I also live in south Jersey and hate when they top my tank off. There's one Shel station by me that actually asks if you want it done or not, but they're like 7-8 cents more than most other staions.



Another thing that makes me mad is when th guy pumping my gas doesnt put the cap in the holster and lets it hang down on to my paint...

 

Off topic, do people in Jersey tip the attendants? I've been there a couple of times on business and tipped, but I expensed it

 

How do you know how many gallons you used?

You let the filling gun click off, and assume the gallons filled is the gallons used, right?

But if that gun is calibrated to shut off late or if you top-off, then you've put extra gas in (compared to the previous time you filled up). You'd be calculating your mpg using 11 gallons, e.g., when you only used 10.9 because the last 0.1 gallon was just extra gas in the tank due to that gun adding an extra 0.1 gallons of fuel during that fill-up compared to the way the previous gun filled up your tank. Vice versa for a gun calibrated to shut off early or if a splash made it shut off early.

 

Unrelated Story:

A guy here at work bought a Jaguar. Not a real Jaguar, but one of those Ford Contours with a better hood ornament. Anyways, his nickname is "Five in the Tank" because that's all he ever puts in, and is happy to stop at the gas station every day. I do not understand this behavior.

One day, about a month after he bought the Contou...err....Jaguar, he gets a Check Engine light. It turns out, there is some sensor in the fuel system that looks to "calibrate" the fill-needle on the dash between Full and Empty. After so many stops at the station with no "fill up", the system was never able to see a full deflection of the arrow, and assumed there was a fault with the system.

Oh, and this isn't covered by warranty, so he got to pay $50 for the experience.

He now fills up once a month, drives the tank down to 1/8th, then does the 5-in-the-tank routine for the rest of the month.

Sheesh.

 

Not true. You didn't use the amount that you are adding. You used the amount you are replacing. Unless you fill it to the exact same level as previously, your mpg calculation will be off.

IMO, the only way to get an accurate mpg is to average several fill ups.

 

After I coast into the station in nuetral [Note: reference to another controversial thread], I always shove as much gas as I can into it, only stopping when it is flowing outof the filler tube like a fountain. At these reasonable prices of 4.17 a gallon, what's a few dollors spilled on the ground.



Oh, and if you hadn't noticed, it was sarcasm.

I stop when the auto shutoff engages.

 

Shoot me if I'm wrong, but topping off WOULD affect your MPG calculation. Here's an example:

Miles driven: 400
Gallons pumped: 12 (the pump auto-stops for the first time)
MPG= 400/12 = 33.3 mpg

Miles driven: 400
Gallons pumped: 13 (topping off with a few extra squeezes on the gun)
MPG= 400/13 = 30 mpg

Difference= 10%

It CAN make a difference in getting a true MPG figure unless you try to "fill up" as much as possible. As mentioned before, some pumps are calibrated to shut off earlier than others. Air pockets in the gas tank may trigger a premature stopping of the pump and leave you a full gallon or two short of "full". Both will throw off calculations.

Best I guess to trust the mpg computer on the car. Or, better yet, try to manually calculate, then compare your result to the computer. If it's close, just trust the computer and relax!

 

I'm curious about that too. The only times I've gone through Jersey, it's been on my motorcycle, and the attendants were more than willing to let me pump my own gas. (Not surprising, since it's very easy to overfill a motorcycle gas tank, even if it's your bike and you're being careful.)

 

However, if you always top off (not to the point where it's spilling out) you'll be filling to the same (approximate) level every time. Thus, topping off (by itself) will not affect your calculations.

 

Topping off is never recommended, as it interferes with the vapor recovery system in the car. Also, I agree that you can't get a perfectly accurate MPG calculation at each fill-up, but averaging three or four fill-ups will give a very accurate result. Over my first four fill-ups I've found my MINI on-board computer calculated MPG to be optimistic by about 1.5 MPG when compared to my own calculations.