gas tank vapor pressure

Asked by Jan 22, 2017 at 11:28 PM about the 2014 Ford Focus SE Hatchback

Question type: General

without an evap system - would a gas tank
explode due to continuuing gas vapors
from gasoline building pressure ? trying to
understand more about how cars work

3 Answers


Depends on the car and the fuel injection system it has. Tanks need to be vented, but the emissions system will close the vent and pull vapors from the charcoal canister at times. Vapors expand on hot days, as well- requiring the venting. Removing an emissions system is extremely illegal, but if you're building a race car or vintage car you may not need to retain all the equipment but there's rarely a good reason to.


No it would not explode under normal conditions, it would take a high heat source, a leak of fuel vapor and and a spark to make it blow, there was a time when fuel tanks had no real venting system, the cap was the vent, then emission systems started and through some vacuum line routing and the addition of carbon canisters those fumes were pulled from the tank and stored in the canister until the engine was fired up and then they were pulled into engine for burning along with fuel, that system was relatively simple but it did leak some fumes off into the atmosphere, so it got more complex, nowadays the fuel tanks actually have a slight vacuum on them while the car is running so there are no fumes trying too escape and the computer monitors the system.


Do a "google" search for gasoline vapor pressure. That will help you understand vapor pressure and how it varies summer to winter.

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