H8R Proof Posted August 10, 2003 Share Posted August 10, 2003 Does this mean overfilling your tank? Quote Link to comment Share on other sites More sharing options...
skeemer Posted August 10, 2003 Share Posted August 10, 2003 It means adding more gas after the auto-shutoff goes. Like you leave it auto filling and it clicks off when it senses that it's full (I believe it measures vapor pressure). It isn't quite full, as you can see if you leave it off for a few seconds then add more. "Topping off" is adding more gas after it shuts itself off. Quote Link to comment Share on other sites More sharing options...
bbsal Posted August 11, 2003 Share Posted August 11, 2003 i think skeemer explained it well.it just means when you put too much gas and its ready to spill out.i do it all the time..lol Quote Link to comment Share on other sites More sharing options...
ProZac Posted August 11, 2003 Share Posted August 11, 2003 at the pump last week, i was able to squeez in another gallon of gas after the automatic shut off! yes topping off. There is more room usually after the auto shut off. its just up to you weather or not you want to, or care to. I do it each time so that i can better calculate my Average miles per gallon for that tank :) As a side note, i was topping off my girlfriend's Civic last year, and was putting the pump back in the terminal at the station and she turned on the car before i put the Gas Cap back on. Gas started backflowing out the hole, i had to put the cap on as gas was comming out to stop it. So! this just teaches you that some women are crazy! The End Just kidding. i just wonder if i didn't top off if it still would have backflowed when turned on without the cap? Brian~ Quote Link to comment Share on other sites More sharing options...
ticman Posted August 11, 2003 Share Posted August 11, 2003 LOL After the auto shut off I top off the tank to the next 25 cents. Don't know why--guess I like my gas bills to be in multiples of $.25 Go figure Quote Link to comment Share on other sites More sharing options...
bartkat Posted August 11, 2003 Share Posted August 11, 2003 I think this has to do with emissions, etc. There may be a slight positive pressure on the tank to help with preventing fumes from going to atmosphere. So if you start the engine with the filler cap off, some gas could slosh out. Once you have the cap on, it's supposedly a closed system. Also, since the tank isn't vented to atmosphere, it's harder to really fill them up. The gas flows more slowly into the tank. If you bounce the car a little and wait a few seconcs, you can get more than a gallon in after the pump shuts off on automatic. They put up the sign "do not top off" to help them comply with EPA. They don't want to take the rap for you running over the tank and spilling gas. Older cars vented the tank to open air, and also vented the crank case fumes to the air. Some cars later on, maybe even now, had the gas tank vented to a little canister of activted charcoal, that was supposed to soak up the bad fumes. Quote Link to comment Share on other sites More sharing options...
SKperformance Posted August 12, 2003 Share Posted August 12, 2003 all cars have to have a charcoal vapour recovory system in tehm there is a slight bulge in all gas tanks at the top to keep some air in the tanks as gas can be compressed unlike liquids so incase of it heating up and expanding this area will take the pressure rather than crack the tank i fill mine all the way up also but i get air miles so i try and get the most i can also the gas pump handles allow air into the tank when filling so it stops before it reaches the filler neck as the bubbles pop to lower the level Quote Link to comment Share on other sites More sharing options...
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