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Old 12-15-2008, 05:29 PM   #41 (permalink)
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Location: vermont
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CivySi - '03 honda civic SI
90 day: 31.99 mpg (US)
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Originally Posted by RH77 View Post
Modern vehicles have an on-board vapor recovery system to prevent fuel vapor from evaporating into the atmosphere and creating "Ozone Alert Days" from the fuel creating inhalation hazards. This may be the "sucking sound" experienced. Some municipalities require the same through the fuel pump itself -- basically a return line at the end the spout returns vapor to the station's supply tank. Between fills, fuel-injected vehicles have a return line to send excess fuel back to the fuel tank from the fuel rail. This is over-simplified, but you get the idea.

In conclusion, I would like to see some hard data (at least 3 tests, repeatable) on the water vapor theory. I admit it would be difficult, but possible to establish significance.

the gas tank is not vented to the outside on a vehicle with fuel recovery. you have a full tank with very little air, then you drain out the gas, whats left? vacume! there is no active air pump that sucks when you open the cap, the vapor recovery is an overglorified fuel tank overflow that runs through a charcoal canister. a motor and pump and entire system to suck air specifically when the car is off would not be feasable and if someone wants to show me in ANY factory service manual where this is shown, or even show a picture of one you pulled out of a car then I'll belive you for that model, but I've never heard of an active fuel recovery system, only passive. fuel expands when its hot and also vaporizes and will pressurize the tank (yes eve when there is a vacume from the half full tank) and will need somewhere to go or explode. you can tell this pretty easily by watching any pre-2007 non-california motorcycle, aka, mine: there is no vapor recovery system, there are two tubes that bleed off the pressure (I belive there is a oneway valve) and you can see and smell gas dripping from these tubes in the summer.

not all vehicles have a fuel return, neither my bike nor my car, nor my previous two cars had fuel return systems, all of them fuel injected.

what do you mean on the vapor theory? that you get more water with an empty tank or filling more? live in the north for a year, you will know when you fill your tank halfway a few times and have frozen your lines after a really cold night, happened last weekend to my wife! she NEVER fills to the top, well, she does now

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