Filling the tank with repeatabilty
 

People usually say to get an accurate reading, you gotta use the same pump at the same station all the time. I think it is because there is a huge difference in pumping speeds between stations.

So heres what I have been doing for years to get repeatable results over pumps from anywhere. And it works really well.

First of all, if the car is sitting considerably nose up or down, itll affect the fill. But I only know of a couple of stations like that, and it only affects me 1 mpg one way or the other. Next tank averages out. I tend to avoid those stations unless the price is better than the others.

Then what I do is always pump the same speed. Which is about 0.1 gallon per second, I just imagine a clock ticking in my head as I watch the gallons readout. Then when it kicks off, I pump about half that speed till it kicks off again, and it usually does in about half a gallon. Then I call it good.

Actually, this started back with one of my old cars, when I had a problem pumping the gas too fast or itd trip the spillover valve and stop the pump. Then I just got used to pumping slower and once I started really logging mpg it came in handy.

Does anyone else do this? Or does anyone else do anything better?

my car seems to suffer from this - sometimes the gauge is stuck way over full, and others at about7/8 full. It seems the load in the car stuffs up the fill as well. It makes for some great mpg numbers - good and bad depending on the previous fill. I always just stop at the first shut off - but i'll experiment with your slow fill method next tank or two and see if it helps - i'll be back in a month or 2 - only ever fill up every 3 or so weeks!!!

Sometimes my Neon tank needs to "burp". So I've taken to bumping the car pretty hard after the nozzle shuts off. Almost always good for another 1.5 gallons...

Wow, I didn't know about this. I guess I've been lucky that I prefer to not only use the same station but the same pump. Does it matter if I pump the gas manually or use the clip on the handle? I usually leave the pump going automatically and wash my windows or check my tires in the meantime.

My car can't even take full speed on the nozzle.. it just clicks off right away.. so i do the following..

The nozzle always goes in a certain way.. otherwise it clicks off early on my car.. seems the filler neck is just slow draining..

I always use the same station.. when I can the same pump.. but all there pumps are the same type.. I set the gas nozzle "cruise control" to the first little notch on the nozzle... let it fill, then when it clicks off I just trickle it in (half of the first notch on the nozzle) till it clicks off again.. the i quit.. It never over fills it but I found that if i didn't trickle it in at the end id get off fills..like .5 gallons difference sometimes.. at 50 mpg that can be a big difference.

I don't think we can 'learn' much from taking mpg readings from one tank of fuel... sure, we might get bragging rights that justify something to somebody (may only ourselves) but we simply can't do accurate enough filling in one tankful to defiatively learn weather or not that latest driving technique or do-dad made 1mpg difference or not... the sample size is too small, the equipment not accurate enough, and the environment is not controlled enough... that's the bad news.

The good news is this, so long as all the fuel from the pump goes into the tank, (not spilled on the ground) and the pump is measuring accurately (controlled calibrations performed (monthly?) by the State Board of Weights and Measures) averaging takes care of the uncertainty of 'how much fuel did I just burn?'. Through averaging you will always get an answer to the question "what's my mpg?" your real fuel usage, which is what you care about anyway.

Keep in mind that the error is proportional to how much you put in the tank. In other words, an error of +/- 0.5 gallons will be 5% if you're putting in 10 gallons, as compared to 10% if you only need 5 gallons to fill it.

Temperature seems to make a notable difference, too. I try to fill at the same time (preferably when it's cool outside) so that doesn't make so much difference.

Make sure you measure (roughly) the amount of nozzle in the filler neck. Some nozzles are more curved than others and some are straight, lastly don't jam the nozzle all the way in the filler, this really distorts the differences between nozzles. ---nozzle rolls off the fingers nice once you've typed it many times.

I use the same pump as often as possible, but it's not always possible. I just fill her till it clicks, and then I go for a second click just it case it clicked early. Usually the second click comes in almost instantaneously. But anyway, in the long run all those variations even up.

In Massachusetts they took those clips way from us. We are not to be trusted! Some people figured out that they could stick their gas cap in the handle to keep the nozzle open, so gas stations put up signs saying "do not stick any object in nozzle for continuous flow".

That's very helpful. Thanks

The temperature in the ground probably wouldn't vary that much, except it's under concrete, which can make a big difference. The other thing is, how long ago was the gas put into the ground from the truck, as the gas could have been a much higher temperature in the truck. So it seems to me that the the early morning is the best time to get gas, after an overcast the previous day, and as long as possible since the ground was filled from the truck.

I pump fuel until I can actually see fuel, it takes a while but is very consistent.

I used to be somewhat serious about using the same pump to the point that I would actually wait for it to be free if someone was there.

One time I got to the station late at night and one other car was at the pump I prefer. So I parked, bought something from the convenient store, and got back in my vehicle. As soon as I started up, somebody else pulled into the station at whatever obscure hour of the night it was...and went to the same pump. :p

These days I'm less particular. I figured that if the goal is to use less fuel, then idling or restarting the engine to get a certain pump - while perhaps good for calculations - isn't worth it. If I can get the same pump I will, but I'll take whatever is free and let the average work itself out.

That's what I do also. It does take a while, but after the first click, I can usually pack in another 1-1.5 gallons. Seeing the gas assures me, in my mind, that I'm going to get pretty consistent calculations.

I only fill up on the way to or from work so I know that the fuel in the neck will get used up. So I don't worry about the rubber neck having gas sit in it too awful long and possibly damaging it in the very long run.

Why do I see signs saying not to do this? Is there an overfill tube? And where does it go? I've been thinking about changing to this method as well.

Filling up past the first auto-click off is just a waste of your money. The auto-shutoff valve sucks the excess gas back into the pump thinking that it won't fit in your gas tank. I was a gas station attendant for several years and I have had classes on this.

If this is the case how can he see the fuel?

it really isn't recommended to fill until you see fuel. It is possible for fuel to get into the EVAP system. If it gets into the charcol canister you will have replace it and that can get expensive. Find a method you feel is consitent and use it every time. I started using wagonman76's method and it has worked fairly well for me. By restricting how much fuel is going through it is a little easier to get more fuel in before the back pressure kick.

J

Can you provide more information about that?

...read for yourself:

Pat Goss: Ask The Expert

...here:

http://www.sbcapcd.org/edu/dtofactsheet.pdf

...here:

http://action.publicbroadcasting.net/cartalk/posts/list/2143473.page

...here:

http://www.mtrinc.com/gasoline_vapor_recovery.html

...and, here:

http://www.epa.gov/ttn/naaqs/ozone/c...ensing(v1).pdf

In the U.S. the department of weights and measures for each state sets , monitors , and enforces the standards for acceptable error.

There is a sticker on the pump that indicates when that specific pump was last inspected.

The old standard was 6 cubic inches per gallon ... which was pretty good ... pumps had to be within +/- about ~2.5% ... if they were off by more than that the pump would be closed down until it passed and the operator would get fined ... most states did not fine more than about ~$500 ... but it does vary from state to state.

The new standard allot of states in the U.S. are going to now is +/- 6 cubic inches per 5 gallons ... which pushes the pumps to being +/- about ~0.5% ... it still varies from state to state... some places still use the older standards ... others have lower or higher fines etc.

So if a pump were off say ~50% when it was tested once per year... the owner might get fined ~$500 ... :rolleyes: ... and have to close that specific pump until it was fixed ... but no notices or refunds to any customers... who might have been ripped off.

Faulty pumps gouging on gas

In 2007 about ~9% of the gas pumps in Arizona failed to pass and were fined ~$300 each ... Arizona checks the pumps in the state once every ~3 years...

So for as long as 3 years there was a pump that was off 200 cubic inches out of 231 cubic inches ... a horrible ~86% error ... for sometime less than ~3 years ... and in Arizona pumps have a maximum fine... $5,000 if a pump is still off beyond that ... they reach the limit ... and in Arizona Operators have maximum fines as well ... and some maxed them out... and even though they were still in violation and their pumps were still inaccurate ... they were not allowed to be fined any more.

It depends on where you live ... I recommend contacting your state department of weights and measure and see what their policies are for pump accuracy ... and what kind of fines ... etc.

I am having a hard time believing that....can you provide some source for this info????

Maybe it's just me, but if I can see the gas, then I don't think it is getting sucked back into the pump:confused::confused::confused: Because if I'm understanding you accurately, then I would be able to stand there all day, continue clicking past the cutoff and never spill a drop.

Now that I think for a moment, I do believe at some stations they have a type of "vapor recovery system" that is supposed to pull the vapors back somehow to help eliminate their escape into the atmosphere as you pump....is this what you are talking about???



And, Old Tele man... thanks for the link. That had some good info in it that I'm gonna have to read through again to make sure I understand how the vapor system works.

...go to the GILBARCO VEEDER-ROOT website; they manufacture gas pump systems. Look under "fuel vapor recovery" for more info about how & why the tanks "suck" back excess fuel at the pump so as to not allow it to get into the air (especially used in California).

...here's what EPA has to say about it (text in yellow box):

http://www.epa.gov/donttopoff/

good info old tele man. I knew it had to do with the EVAP system, but didn't know all the specifics.

http://www.epa.gov/oar/oaqps/greenbk/map/mapnmpoll.jpg

humm

Air Quality Forecast Guidance for CONUS Area

...best advice, do as one of our presidents did: "...don't inhale..."

So (1) the vapor is fed back into the station's storage tanks, regardless of much gas you get and (2) any gas you pump into your tank may also be drawn into the station's storage tanks. I don't quite get why it would only be "additional" gas. I wonder at what point this would happen, after the 1st click? the 2nd click? from the time you first put the nozzle in the tank?

If there is no difference at any time, then it doesn't matter how much the tank is filled up. If it's only when the gas reaches a certain level, then this depends on where that level might be.

Interesting, the stations might be fined a nominal amount if the pumps are found to provide less gas than paid for; however they are also encouraged to take gas back from the cars and to put it back in their storage tanks!