Proper fill-up?

[froggy81500]

Just as the title implies. When you are filling your car up, do you stop when it kicks off the first shuts off, or do you top it off? Mind you, I do not have a scangauge, I just use the simple math to figure my MPG and keep it in a spreadsheet. I ask this right now particularly because I filled up on Friday or Saturday, and at the gallons when the pump first kicked off I was right around 40MPG, but I topped it off and brought it down to 37.2.

Up until this point, I usually always top it off and I run the tank pretty low. With a 13 gallon tank, I am normally refilling with at least 11 gallons.

I would like to hear from anyone regarding this. But I am very intersted in hearing from those who use a scangauge to see how accurate their gauge is with respect to gallons used and what it actually took to fill it back up to when the pump first kicks off.

[theholycow]

It's tough to get consistent, accurate fills with topping off, so I stop at the first shut-off.

[thornburg]

The most important thing is to be consistent. If you always top-off or always stop at the first shut-off, you should be OK. If you alternate between them, then your economy will go up and down as the amount of fuel required to "fill" the tank changes.

Note that there will be some differences anyway. If you always fill at the same station, using the same pump, you'll get minimal differences. If you fill at different stations all the time, you will get larger differences.

No matter what you do, looking at long terms trends (5 or more fill-ups in a row) will even out these differences and give you a true picture of your overall economy.

[BEEF]

some people will say to use the same station and the same pump and fill up the same time of day. that is the best way to do it.

at the same time, if you are like me, you need to fill up in different places and different cities at different times of the day. I use the "first shut-off" method and have had good results. the best thing is an overall average. that way the err is averaged out. if you have a difference over one tank, lets say 13 gallons, that difference will be much smaller over 130 gallons or the equivalent of 10 tanks of gas. in the same respect, the difference could be huge with only 3 gallons. I have seen people claims great mpg using just a few gallons of gas.

that is the beauty of the gas log. it will average it for you. most people (not all) have fluctuations in their gas logs. one tank will look great and the next won't if you average out the two tanks, you will get a better idea of what the true mileage is.

I have a scangauge but still use the calculation method because of accuracy. the scangauge calculates MPG using air flow (this is something new to me too) so I have had it where my calculated mpg was better and worse (not at the same time) than what the scangauge was reading. I like to think of the scangauge as a good indicator. I still use the trip odo and gallons used method.

*edit* crap, slow to post didn't see the post before mine

[ihatemybike]

Here's the way I do it.
Fast set to click off
Wait 5 seconds
Slow set to click off
Wait 5 seconds
Fill to next dime

[Jay2TheRescue]

I always stop at the first click. Overfilling the tank can cause problems with the vapor recovery system on the pump, and recirculate gasoline which will make your mileage appear lower than it actually is. Overfilling the tank can also cause problems with the vapor system on the vehicle as well.

[froggy81500]

I understand consistency. I realize that if I suddenly start going by the shut off and not top off that my results will look skewed for a bit since I've usually topped off in the past. And for the most part I do go to the same place for gas. Not always the same pump though. I know here in NY anyway that gas pumps are tested every few years for accuracy so I am not worried about inconsistencies between different pumps or even stations. It should not be that big of a concern with such a small amount of fuel in relation to how much they dispense overall.

I've seen what you are referring to about some with just small fills and showing big numbers. The problem lies with margin of error on the calculations. This margin is much smaller when running the tank down and filling it all the way back up, as opposed to running down a couple gallons and then topping off again. Consider that many vehicles can squeeze another 1/4 gallon, if not more, after the pump shuts off. A 1/4 gallon difference makes a big difference if you're talking only 2 gallons (+/- 12.5%), whereas it is not so significant when we are talking 10 gallons (+/- 2.5%). For that reason is why I believe

[theholycow]

Originally Posted by froggy81500

gas pumps are tested every few years for accuracy so I am not worried about inconsistencies between different pumps or even stations.

That only tests that they measure the pumped amount of gas accurately, not that they shut off at the same point.

For accurate and consistent MPG calculations, you want it to shut off at the same point so it reaches the same level in your vehicle every time. That means the best accuracy is on the same pump, same side, facing the same direction every time.

[thornburg]

Originally Posted by theholycow

For accurate and consistent MPG calculations, you want it to shut off at the same point so it reaches the same level in your vehicle every time. That means the best accuracy is on the same pump, same side, facing the same direction every time.

It's the Feng Shui method of gas logging!



OTOH, you are absolutely right about the shutoff variation. The only description I've heard of the test for pump accuracy involved pumping exactly 5.000 gallons of gas (according to the pump) and measuring it some other way (I don't remember what, maybe just a demarcated container). It doesn't use the auto-shutoff, which will still accurately measure how much was added to the tank, but won't accurately measure how much was used.

[Jay2TheRescue]

Originally Posted by thornburg

It's the Feng Shui method of gas logging!



OTOH, you are absolutely right about the shutoff variation. The only description I've heard of the test for pump accuracy involved pumping exactly 5.000 gallons of gas (according to the pump) and measuring it some other way (I don't remember what, maybe just a demarcated container). It doesn't use the auto-shutoff, which will still accurately measure how much was added to the tank, but won't accurately measure how much was used.

Yeah, they use a special calibrated container to measure the gas pumped. The pump needs to read 5 gallons when the container is full.

-Jay

[67 Satellite]

Unless I'm out of town, I always fill up at the same pump. I always lock it flowing as fast as it will go,then when it kicks off I round it up to the next 25 cent incriment.

[cems70]

I stop filling when the pump stops. Only rarely am I able to fill up at the same station and pump (which others have noted is the best way to assure consistent fillups). I try to put about 3 - 4 inches of the nozzle into the filler neck, regardless of which station or pump I'm using. I usually accomplish this by pulling the nozzle out of the tank until the bottom most ring at the base of the nozzle spout (I don't know if other parts of the country have this...it looks like a spring wrapped around the base of the nozzle spout) rests on the lip of the filler neck. I then pump slowly to ensure a full fillup with little air mixed in. It's not always a full proof filling method, but it seems to give me relatively consistent results. The pump usually stops as the gas is gurgling at the top of the filler neck (often visible as the pump stops).

Originally Posted by Jay2TheRescue

I always stop at the first click. Overfilling the tank can cause problems with the vapor recovery system on the pump, and recirculate gasoline which will make your mileage appear lower than it actually is. Overfilling the tank can also cause problems with the vapor system on the vehicle as well.

Not true for me. I used to regularly overfill my 1995 Civic VX by as much as 5 gallons. After the pump stopped, I could trickle in another 5 gallons. It never hurt my fuel economy or anything on my vehicle.

[monroe74]

Originally Posted by Jay2TheRescue

Overfilling the tank can cause problems with the vapor recovery system on the pump, and recirculate gasoline which will make your mileage appear lower than it actually is.

Just to emphasize this point and be really clear about what it means: when you overfill, gas will be sucked back into the underground tank, via the nozzle's vapor-recovery system (those little holes near the tip of the nozzle). So you can very easily pay for gas you are not getting. The pump does not calculate a refund when the gas is being sucked back up through the vapor-recovery system!

So yes, this "will make your mileage appear lower than it actually is." And you will also be paying for fuel that you never get to burn.

Originally Posted by cems70

The pump usually stops as the gas is gurgling at the top of the filler neck (often visible as the pump stops).

Gasoline expands when heated. So if you just pumped fuel from a cool underground tank, and then go park your car in the sun, this could create a problem, if you really filled the tank right up to the very top.

I used to regularly overfill my 1995 Civic VX by as much as 5 gallons.

You must mean 0.5, not 5, right?

And even if you're just 'overfilling' by 0.5, I think that means you were probably sending some fuel into the pump's vapor-recovery system.

When the nozzle clicks off for the first time, I'm done.

[Jay2TheRescue]

Yeah, when I was in college and worked at a fuel station we had the station upgraded to vapor recovery. We were told that if you tried to top off the tank that it was possible to pump 20 gallons in a car with only a 15 gallon tank. You're paying for gas that you don't get.

-jay

[froggy81500]

I know about the vapor recovery and the shut off piece on the inside of the hose. Not sure if stations here in NY use the same like I have seen in other states, the nozzles having that boot or whatever over them. We don't have them in NY. I used to work at a station for about 4 years. Occasionally we'd get a nozzle broken where the shut off hose was just hanging inside the nozzle and no longer attached to the end and when that happens the pump keeps kicking off constantly.

[cems70]

Originally Posted by monroe74

You must mean 0.5, not 5, right?

And even if you're just 'overfilling' by 0.5, I think that means you were probably sending some fuel into the pump's vapor-recovery system.

When the nozzle clicks off for the first time, I'm done.

No, I mean 5.0 gallons. I could trickle in another 5.0 gallons after the nozzle clicked off the first time. And I don't think I was sending any fuel into the pump's vapor-recovery system either.

I used to be very good at knowing how much gas was remaining in my tank. So if I filled up the tank, it usually took 9.5 - 9.9 gallons before the nozzle clicked off. If I did not add any more gas after it clicked off, I would get about 510 - 520 miles before my next fillup (if i was getting my usual 54 mpg). If I trickled in another 5 gallons after the nozzle clicked off, I assumed I had about 14.5 - 15 gallons of gas in the tank. And sure enough, I could go about 780 - 810 miles until my next fillup. and my FE was the same 54 - 55 mpg. This tells me that ALL the gas that I trickled into the tank after the nozzle first clicked off was going into the tank, not into the pump's vapor recovery system. When I trickled the gas into the tank, the tip of the nozzle where the holes are was never submerged in the gas in the filler neck. The filler neck gas always settled back down. I was never able to completely fill the tank to the point where I could see the gas floating in the filler neck.

I've always been preplexed by this penomenom in my VX (and now my 1995 Civic DX) of being able to add 50% more gas to the tank.

[monroe74]

Originally Posted by cems70

No, I mean 5.0 gallons. I could trickle in another 5.0 gallons after the nozzle clicked off the first time.

Thanks for responding. This is interesting. I think you once said something about this on another thread, and I appreciate the extra detail you're mentioning now.

And I don't think I was sending any fuel into the pump's vapor-recovery system either.

I agree. I once calculated the maximum possible capacity of the vapor-recovery canister (based on its external dimensions), and it was quite small. Less than a quart, I think.

So if I filled up the tank, it usually took 9.5 - 9.9 gallons before the nozzle clicked off.

Sounds about right. I'm pretty sure your car has a 10-gallon tank. I have the same car, and I once ran the tank dry on purpose, and confirmed that it's 10 gallons.

sure enough, I could go about 780 - 810 miles until my next fillup

Are you sure about the numbers? According to your gas log, your longest tank was 720.3 miles. That's still a lot, though.

When I trickled the gas into the tank, the tip of the nozzle where the holes are was never submerged in the gas in the filler neck.

If those holes are never submerged, then I agree with you that gas is not getting sucked back into the pump's vapor-recovery system.

I was never able to completely fill the tank to the point where I could see the gas floating in the filler neck.

That's an interesting observation. Because at some point it seems that the gas would have to reach that level.

I've always been preplexed by this penomenom in my VX (and now my 1995 Civic DX) of being able to add 50% more gas to the tank.

I agree that it's pretty mysterious. Here's one theory: for some strange reason, your car's tank is 12 gallons, not 10. (Maybe a prior owner did a swap.) I notice in your gaslog that there are only a few times that you pumped over 12 gallons. But your gaslog does indicate you pumped 15 gallons on two occasions. That's definitely a mystery, given that you were careful not to submerge the vapor-recovery holes in the nozzle.

I once pumped 12 gallons into my 10 gallon tank, but I wasn't being careful to prevent those holes from submerging. So I think I was mostly sending gas into those holes.

Anyway, if you learn more about what's happening, I hope you'll share more details.

[cems70]

Originally Posted by monroe74

Are you sure about the numbers? According to your gas log, your longest tank was 720.3 miles. That's still a lot, though.

The gas log you see is for my '95 Civic DX hatchback, not my former '95 VX which I sold 1.5 years ago. You're right that the VX had a 10 gallon tank. I had several 10 gallon fillups after almost running out of gas. I have no explanation about how a 10 gallon tank can take another 5 gallons of gas after the nozzle clicks off. And the same is true for the DX as you saw from a couple of 15 gallon fillups.

[Jay2TheRescue]

Originally Posted by cems70

The gas log you see is for my '95 Civic DX hatchback, not my former '95 VX which I sold 1.5 years ago. You're right that the VX had a 10 gallon tank. I had several 10 gallon fillups after almost running out of gas. I have no explanation about how a 10 gallon tank can take another 5 gallons of gas after the nozzle clicks off. And the same is true for the DX as you saw from a couple of 15 gallon fillups.

Because if you overfill the tank the vapor recovery system on the fuel pump will suck up the excess gasoline if you try to force more into the tank. Once the tank is full if you continue to try to pump fuel you are just recirculating gasoline, and wasting your money.

-Jay

[R.I.D.E.]

cems70;

Looking at your gas log your mileage seems to be consistent with the 15 gal fill ups, so it makes no sense that your fuel was going anywhere but in your car.

If you were pumping any fuel back into the stations tank your mileage would have dropped off dramatically, which it did not.

I have no rational explanation for the 15 gallon fillup, but your average mileage did not change significantly.

I do know that certain vehicles will shut off the pump when there is a lot more room for fuel in the tank. My wifes Murano is that way, to the tune of 2-3 gallons.

In my case when filling I listen for the noise when the fuel starts to build up in the filler neck, stop the pump for a few seconds then finish at about 3/4
speed intil it shuts itself off. I can see the fuel splashing around the opening but I dont have any spilling out of the filler neck.


regards
gary

[monroe74]

Originally Posted by cems70

The gas log you see is for my '95 Civic DX hatchback, not my former '95 VX

Oops, my mistake. Thanks for pointing that out.

Originally Posted by Jay2TheRescue

Because if you overfill the tank the vapor recovery system on the fuel pump will suck up the excess gasoline

That's been my experience, too. But he claims that he was being careful to make sure the vapor-recovery holes (near the tip of the nozzle) were never submerged. Also he says that his overall mpg was consistent with the gas actually entering the tank. So I think these factors turn the situation into a mystery.

[Jay2TheRescue]

LOL, my old AMC Spirit did that... It was a tiny hatchback with either a 21 or 25 gallon tank. I don't remember now. It would click off the first time when there were about 15 gallons in the tank. If you clicked the pump back on you would usually get another 5 gallons in at least, and this was before vapor recovery, so everything did go in the tank. It was funny to be with grandma when she put gas in the car. It would click off and grandma would yell "Keep Pumpin'!" The attendant would usually respond with something to the effect of "Its a little car lady.", but sure enough you could get several more gallons in after it clicked the first time. I remember it was nothing to get 700 or 800 miles to a tank in that car.

-Jay

[Ford Man]

I think the reason for getting several more gallons of fuel in the tank after the pump shuts off is because the car manufacturer measures the tank capacity to where the tank float stops and on some cars that is a few inches from the top of the tank plus the amount that you get into the filler neck. My '88 Escort has a 13 gallon tank but I have put slightly over 14 gallons in it before and wasn't completely out of gas when I did it, because I drove the car into the gas station. The 14 gallon fill up was topping off the tank. I can usually get between 1 and 1 1/2 gallons in after the pump first kicks off. I also remember that the gas gauge was a little below empty when I put the 14 gallons in it.

[thornburg]

Yeah, the other responses are headed in the right direction with this: Your fuel tank is basically 'rated' for a certain capacity -- this is not actually a measure of how much it holds, but of how much they expect it to take before the pump shuts off, and is the "recommended" fill capacity. The tank will hold a little more, plus the filler neck, and some vehicles (such as VW TDIs) have a "vent" that can be used to let pressure out of the tank and fill more easily (and in TDIs, this mechanism could be removed to even further increase the capacity--google "ventectomy"--note that this could apply to all VWs, I wouldn't know, as I have never owned a gas-powered VW).

Despite all these various other places that fuel can go, I don't believe you generally should exceed your tank's rated capacity.

If you are about to hop on the highway and drive 500 miles, then it might be worth it, but, personally, I don't think it is worth the potential of extra wear & tear, spillage, etc in regular daily driving.

[joeventura]

Stop pumping when the handle clicks?
I have had an empty tank and the handle clicks after half a gallon.

And its not practical to say use the same pump at the same station, that's good in an ideal world where you never have to drive anywhere further than half the distance of a full tank.

The method I use is quite simple, look into the filler port while pumping, the first time you see gas (i.e. it bubble up to the top) then stop.

Don't round to the dime or the dollar, when you see the gas, you are full.

[theholycow]

Originally Posted by joeventura

And its not practical to say use the same pump at the same station, that's good in an ideal world where you never have to drive anywhere further than half the distance of a full tank.

Well, it's not THAT rare; it's just that it's most useful to say in the context of repeatable experiments. I commute the same way every day, and I do get gas on the same side of the same pump every single time. In the last three months or so, I have had to wait for that pump once. Every other time I just roll right up to it. Obviously it's more difficult for people in busier areas or people not on the same route.

[99metro]

Originally Posted by joeventura

Stop pumping when the handle clicks?
I have had an empty tank and the handle clicks after half a gallon.

And its not practical to say use the same pump at the same station, that's good in an ideal world where you never have to drive anywhere further than half the distance of a full tank.

The method I use is quite simple, look into the filler port while pumping, the first time you see gas (i.e. it bubble up to the top) then stop.

Don't round to the dime or the dollar, when you see the gas, you are full.

Sorta agree with this. My diesel might click off 3 or 4 times depending on how dirty their filter is, what angle I have the fill nozzle, and much pressure the pump has (if there a more than one person pumping from the same tank, the flow/pressure drops). Sometimes I am clicking off .2 gal a second, and sometimes I'm clicking off .05 gal a second. Something to take note of. This WILL affect where the pump auto stops.

So, MY thoughts are to pump at a consistant flow till the autoshutoff, then one more click to ensure it's not a premature stop. Pick something you can be consistant at, like .1 gal a second or .2 gal a second. The very very very accurate way to ensure a full tank is to keep filling until you get spillage (but I wouldn't do this in practice! - nor recommend it). Unless you see the gas through the hole, you can be off by as much as a gallon to a gallon and a half before actually being full.

In summary, do the same thing every time and be consistant.

and that in my opinion is that

[PaleMelanesian]

Has anyone tried using a dipstick to check the fill level?

[R.I.D.E.]

I like it, a dipstick for your gas tank.

Actually I was thinking about a drip feed tank that would connect to the filler neck. Make a separate fitting into the filler neck about 4 inches from the top, and connect it to a separate tank which would drip feed gas into the main tank when the level dropped below your tube.

Then you could weight the test tank before and after for precise fuel consumption.

regards
gary

[R.I.D.E.]

Actually you could use a piece of clear tubing and a golf tee. mark the tubing at the point where you want it to be at the top of the filler neck, stick it in the neck and stick the tee in the end of the tube. Pull the tube up to see where the fuel level is located. Make the tube long enough so it will stay under the fuel level as you check it.

regards
gary