I remember reading somewhere that it was stupid to top off at the pump (as well as illegal in some states). Beyond the possibility of overflow/spillage, please refresh my memory (such as it was…) about why this is dumb.
continueing to pump fuel after the nozzle drops out can push fuel into the venting system, causing raw fuel to damage it.
And, the heart of the fuel tank’s venting system is a carbon canister. When the canister becomes contaminated as a result of overfilling the tank, it must be replaced to the tune of a few hundred $$.
Some make/models are susceptible to damage by overfilling. The venting system suffers. Other cars are totally immune to this situation (as they all should be). So some people are able to fill to the tippy-top without problems, others simply can’t… or shouldn’t.
Topping off the tank can cause fuel to get into the carbon canister that absorbs fumes before they get to the atmosphere as already stated. If that gets saturated with fuel, then air cannot get into your fuel tank. No air into your tank, then fuel cannot leave your tank and your car’s performance drops accordingly. They are not cheap to replace and can really ruin your day/plans. So is that extra drop of fuel worth the risk? No.
And of course there really is very little reason for wanting to fill to the very top. After all if it was really important to you to get as much gas in there as possible, you would have checked out the size of the tank before you bought it, and I’ll bet you did not. It just is not important to top it off, but it can be costly.
Note: my messages is directed to people in general and I did not redwine or any one in particular.
YOU’VE GOT MONEY TO TOP OFF A TANK!!!
Almost all canisters are well below the fill port of the tank. Not hard to figure out. Gas comes out of underground tanks. When it warms up it will expand, better have some space to put it.
Charcoal cannisters can cost over $400 to replace!
I do this often with two different Chevrolets to get the most gas in at a good price or to go as far as possible to the next fill. No check engine light; no problem.
Agreed, good reasons. Most cars never have a problem with topping up. Which ones? Well, every car I’ve ever driven.
My 1989 Dodge Caravan at times would get real smelly of gasoline. I asked my Master mechanic in Iowa, and he said I was overfilling the tank, as described here. But on that model he said it would clear itself up, and so it did when I stopped being dumb.