Then how does the gas vapor/fumes get to the canistor in our cars if there is a vacuum instead of pressure?
I think your scenario is the paranormal one. A tank that is sitting in hot weather with winter gas in it (9.0 rvp) can build enough vapor pressure to push fuel, but it would be a rare occurence for that pressure to overcome the vacuum being pulled by a running mechanical fuel pump. Fuel simply will not build vapor pressure that fast. If it could, then you could run the engine on the vapor alone. To answer your question: The fumes get to the cannister while the vehicle is parked and not in use.
another example of building pressure... I went to the coast with a friend in a big Bronco to pull a large boat back to his shop (175 miles) for repairs . on the way back the exhaust pipe had rotted off in a turn next to the tank. the exhaust was blowing on the tank. when we stopped to refuel the gas was boiling in the tank and steam was coming out of the filler neck when we removed the cap. the first few seconds of refueling it would bubble back out. after getting enough in to cool the tank it filled on up. we came the rest of the way with the cap loose so the steam could escape... ...drinking and smoking "buds" took the edge off of worrying if it would blow... ... man...
Good thing y'all stopped for fuel when you did, otherwise y'all were minutes away from making the ten o'clock news. That was not steam coming out the filler neck.
SO FAR, it seems to drive OK without the gas cap! But its HARD to find a NOS deluxe gas cap, mine still looks new!
See Post #9 on this thread http://mmb.maverick.to/showthread.php?t=62680&highlight=vented+gas+cap You can turn your unvented cap into a vented cap.
Well SOOO far it hasent flooded with the gas cap off. Im going to knock out the spring and button on my gas cap and PRAY it works. CHaz.
