Here is a question for you guys. It is not necessarily related to any specific Lexus model but since my race car has a 1UZ I figured I would ask it here. What is the proper design for a vented or non-vented gas tank? Like how much pressure or vacuum should be present? Should it be designed kind of like a sealed cooling system to where there is a gas overflow at a certain pressure and then it will suck it back as a vacuum is created. I have heard of people saying that the gas cap should allow air in but nothing out. This makes sense as your fuel is consumed air has to be let in otherwise your gas tank collapse under the vacuum. (Kind of like drinking water from a plastic bottle but not letting air into the container while drinking) But on the other side should there be a certain pressure that your gas tank should have or a maximum pressure that it should have.
I ask because on my race car I essentially have a sealed fuel filler cap but on the fuel filler neck I have a small tube that runs to the ground. So pressure can not build up in my tank from the fuel vapors. This makes sense but when I fill up the tank and run the car for a short period of time I sometimes get fuel overflowing out of this tube to the ground. Is the gas tank simply heating up to much allowing the gas to expand and run out of the overflow tube due to overfilling the tank or is there supposed to be a certain amount of pressure allowed in my gas tank? It would almost make sense for me to put a small one way valve (check valve) in the overflow tube path. That way it will let air in to prevent the tank from collapsing but it would allow a certain amount of pressure to build in the tank without having gas overflow out every time. Or should I just not fill the tank up all the way or put a small catch tank so the fuel has somewhere other then the ground to go? What is the proper way of doing this?
