Some Questions Related To Fuel Fillups

[LUVMY02CREW]

I did some searching and didn't/couldn't find some info....I'm trying to keep a running record of mpg and am trying to be accurate with how much fuel I put in.....

Regarding filling up, I usually try to wait till 1/2 or less, with erratic fuel gauge I don't want to risk running out. I don't really try to guess when gas prices may go up/down, cause I'm gonna need it regardless of the price on any particular day, so if it's time I fill up.

After dropping off 2 of my kiddos at their schools, I commute to work and still have some time left over, so this is when I fill up: in the mornings, same station, I even try to get the same pump if possible, same octane, etc... I try to keep it same to help eliminate any possible variables when filling up.

I also try to top off each tank, all the way up so I can see the gas at the flapper thingy in the filler hole. This way I know I have a FULL tank. I have noticed that even at the slowest notch on the handle, after it clicks, that the remaing amount I can squeeze in can vary from 1 to 2.5 gallons, which can affect mpg numbers significantly. I don't have any leaks when filling up like I read in a couple of threads.

So.... I guess some questions related to fillups are...

1 - Is topping off a good/safe thing to do to keep an accurate record of fuel used?
2 - Are there alternatives to topping off to be accurate?
3 - Would there be be any possible safety/mechanical/other drawbacks to topping off?
4 - Any other questions somebody else might have........?


I know gas pump police put the warning on the handles to try and keep me from doing this, but I guess I'm just a little rebelious sometimes

[HenryJ]

I quit at the first shut off. No topping off.
We do need a little air space.
Possible problems might be expansion on a hot day. Flooding the evaporative emissions charcoal canister. Degradation of the rubber in the filler tube.

Those are a few things that come to mind.

I , personally, have responded to calls of fuel leaking. At least twice this has been an over filled tank sitting in the sun.

Average three tankfuls for a good MPG estimate.

[roadrunner]

Perhaps a Scan Guage II would be an option for you to track your mpg's.

[Rockrz]

Possible problems might be expansion on a hot day

Wasn't GM smart enough to think of this and make the gas tank vented to accomodate expansion?

I've always topped mine off, even shake the truck back and forth to remove all air so I can get as much in as possible and never had any problems.

It's a '96 with all original parts as far as fuel tank, filler neck, etc.
Never has any leakage either. I'm in Texas too where a car sitting in a hot parking lot can get up to 130 degrees in the summer, or more.

I always figured the fuel system was vented so as long as I've been driving I've filled it up with as much as I can possibly get in the tank.

Surely the manufacturers know that heat expands and they've planned for that I would think. Right?

[LUVMY02CREW]

I just started doing this a couple of months ago, so we haven't had any really hot temps to expand the fuel I guess. I hadn't thought about the effect on the rubber.

Is this the canister you're talking about? http://www.s-10crewcab.com/phpBB2/viewt ... l+canister

I hope to be getting a scangauge soon.

I've always topped mine off, even shake the truck back and forth to remove all air so I can get as much in as possible and never had any problems.

I can just imagine the looks you get sometimes while shaking your truck at the pump

Thanks for replys

[Rockrz]

I can just imagine the looks you get sometimes while shaking your truck at the pump

I just tell 'em it makes air bubbles in the gas, helping the gas produce less pollution, which decreases global warming and helps save Mother Earth so our children can live a long happy productive life in world peace!

Then, I ask 'em to go to my tool box and get my pair of wire stretchers cause I cut a wire too short, and while they're at it bring me my metric cresent wrench cause I have some metric bolts to tighten...

Nah, them old timers know I'm getting excess air out of my tank so I can get more gas in.

The young'uns are too busy sending text messages to know or care.

[HenryJ]

Is this the canister you're talking about? http://www.s-10crewcab.com/phpBB2/viewtopic.php?t=6108

That is the vent valve. It attaches to the canister. It may be possible to flood that with an over filled fuel tank. That could lead to several problems.
Jiggling to get all the air out and pack more fuel is something I used to see old farmers do before the trip back to the ranch.
What ever makes you feel better.
I added auxiliary tanks to carry more fuel, some people jiggle their truck.

[Rockrz]

I think mine must have come "Redneck Equipped" cause it's never been
a problem on any of the vehicles I've driven over the past 28 years of driving.

[HenryJ]

These are just not the same as older vehicles. Our filler neck extends well above the fuel tank and evap canister. Crew cabs are worse than most for a very long filler neck due to the Isuzu bed.
Newer vehicles are designed to trap fuel vapors in the evap canister. This is mounted barely above the top of the fuel tank. filling up into the filler tube you add fuel above the canister level.
Maybe you will continue to have no problems. Some are not always as lucky.

Fuel is still pumped by attendants here. They are trained to stop when the pump quits. Not to "top off".
I guess you can tell I agree with that practice.

[LUVMY02CREW]

Rockrz - good explanations

HenryJ - I guess a slide under the truck is in order for the weekend to check out those parts you are talking about. And, we haven't had attendents down in this area in a really, really long time, that is unless you want to pay Full Service price and take an even bigger hit in the ole wallet.

I also got to thinking more about the whole expansion area thing. What if I change my fill up location to before I make my commute(still fill to flapper for extreme accuracy)??? This way the commute will use up the "packed" in gas, so it'll only be in neck for a little while, and the expansion area is there for the daily sun heatup.

Just thinking outloud on this, but theoretically does this seem reasonable?!?!?

[04crewvt]

I fill till the pump clicks off and that's it. If you do this every time your MPG will be as accurate as any other way. Topping off to the top of the filler neck is dangerous, the filler neck is not protected like the tank and it blocks the vent (thats what the click off on the pump is there for. Gas needs room for expansion in hot weather, the air in the filler neck gives some breathing room to the tank. All you get by filling to the top of the neck is the most miles from a tank. Most modern gas pumps have vapor recovery systems built into the nozzles to prevent volatiles from the gas entering the atmosphere, topping off defeats the pumps safety features .

[sonomaextcab]

oopps i top off every time. but after about a hundred miles or so I open the gas cap, but its not under pressure. I believe its my new fuel cap I bought when we had someone stealing gas in this area. I lost $30 in fuel in one night, I was not a happy camper.

[HenryJ]

... I open the gas cap, but its not under pressure.

Venting takes place through the carbon canister with the regulation controlled by the evaporative vent valve.
Flooding this system with fuel was my concern.

[Horsehammerr]

OH YEAH !!