Anything wrong with filling up into the tank neck?

[lyd]

Heh. Can't seem to phrase that quite right. How many of you read that subject and thought, "well, where else would you put it?"

What I mean is, adding fuel until the level rises up into the neck. I vaguely remember having once read that this was bad practice, but I can't remember why and googling on the topic just now didn't enlighten me.

The reason I want to do this is that between the notoriously inaccurate Geo gas gauge (Just yesterday I found out I have a 10 gallon tank! For years I've thought it was 8 gal because that's what it takes when the needle is solidly at the bottom of the red.) causing me to fill up early, the tendency for any pump to kick off unpredictably when filling this car, and a small tank size in any case, the percentage variance between one fill and the next can be so high. In order to try to be more consistent I've started, with the last fill, continuing to pump gas into it until I hear it come right up into the tank neck. Seems like that should help get the variance down to a reasonable margin. I've been doing the same pump, same direction thing all along, of course.

Any trouble with this?

[dremd]

it will very likley kill your evaporative emissions canister, that is if you have one; otherwise you will dump fuel either on the ground or down your intake.

Us diesel guys do it; but diesel doesn't evaporate nearly as easily.

[ac7ss]

dont forget thermal expansion in the summer. Dremd is right abuot your emissions system if you are filling up to the throat. if you are just filling to the base of the fill tube, you should be ok.

[MetroMPG]

I've been in the practice of doing this (filling to the top of the filler neck) since day 1. Not aware of any adverse effects.

[wagonman76]

Originally Posted by ac7ss

dont forget thermal expansion in the summer. Dremd is right abuot your emissions system if you are filling up to the throat. if you are just filling to the base of the fill tube, you should be ok.

Thats the main reason I dont do that, I would worry about losing gas due to expansion. Not only summer, but I would think that the expansion from -20F to 20F would be the same as 50F to 90F.

To try to minimize the difference between pump shutoffs, I count seconds to myself and pump at about .1 gallon per second. And I go to the 2nd clickoff. The only time I get a bad fill is when the pump is broken and the shutoff doesnt work and it overfills. Also, before even getting out of the car, I make an educated guess of what itll take to fill the tank to start with, so if it kicks off way too soon or not at all, I know somethings up. Also if the car is on a slope, itll affect the fill a bit depending on where your fill tube enters the tank.

[lyd]

Hmm. Regarding expansion, if I just make sure to fill up on the way out to drive rather than on the way home to park, does that pretty much solve it? Even with the Metro's mileage, it can't take long to burn through that bit of gas.

The canister problem I don't understand. Could someone expand on how this could kill it? I don't understand the dumping fuel into the intake comment either.

There is some possibility my canister might be dead anyway. I read a comment recently that suggested that with a functioning canister your tank won't ever go psssshhhhht when you take the cap off, and mine does sometimes.

I won't have as much of an issue with this once I have settled into a routine and am more concerned about averaging over several tanks anyway, but right now I am trying to get some good baseline data as soon as I can.

[dremd]

Originally Posted by lyd

Hmm. Regarding expansion, if I just make sure to fill up on the way out to drive rather than on the way home to park, does that pretty much solve it? Even with the Metro's mileage, it can't take long to burn through that bit of gas.

You are probably correct, but that would depend on the necks shape

Originally Posted by lyd

The canister problem I don't understand. Could someone expand on how this could kill it?

Sure thing

Essentially the evaporative emmissions canister is a charcol filter designed to catch fuel vapors esc aping from your tank, collect them, then release them in to your intake manifold to be used as fuel when you strart the car.

Issue is that they are designed to work with gas/ vapors (the state of matter) if they receive liquid fuel (at least in the case of my 87 supra) the charcoal turns in to mush and no longer does its job.

Originally Posted by lyd

I don't understand the dumping fuel into the intake comment either.

If your car doesn't have an evaporative emissions canister, then chances are the vent line goes straight to the intake (air cooled vw did this) If i filed it all the way up I'd get surging while cornering left due to the liquid fuel being poured down the carburetors throat.

Originally Posted by lyd

There is some possibility my canister might be dead anyway. I read a comment recently that suggested that with a functioning canister your tank won't ever go psssshhhhht when you take the cap off, and mine does sometimes.

Going t ask someone else that one.

[lyd]

Thanks a lot for the reply. I see what you mean about the canister.