Originally Posted by floyd
For many years now I have used that flap in the filler neck as a trivia quiz. We are now a couple of generations from 1974 when it was introduced. The government doesn't know how to eliminate old law once it becomes obsolete.
That device was introduced in 1974 to prevent the introduction of leaded gas into a car with a catalytic converter.( lead kills converters) To this day, unleaded nozzles are smaller than the leaded gas nozzles which no longer exist in commercial fuel sales.
Refineries have long since ceased production of leaded gas, yet the restricter persists like a piece of useless folklore.
A fuel tank rollover valve is another item altogether and would not affect siphoning.
Floyd, some time ago I had a problem siphoning gas from my 2012 Tacoma and contacted the folks at Gas Tapper as I didn't want to inadvertently damage something in the filler tube. It was my recollection their advice made reference to possible interference from a check valve which prompted the wording in my post. I didn't save those emails but your response got me to thinking so I went back to the link I provided and read it in more detail. This excerpt may be of interest to you.
"Many people have tried to siphon gas out of one of their newer vehicles only to find out they hit one if not two major difficulties. It is not easy. Most newer model cars and SUVís have emergency valves that stop gas from draining out in the event of a roll-over. This valve also acts as a siphon prevention system which is the reason why nearly all the siphon devices and pumps sold these days are useless. That being said, there is a way to siphon gas from a modern car, you just need to know how to do it and have the right tools for the job.
The anatomy of the blockage in newer vehicles is a ball valve or butterfly valve. There is enough room for gas to get through the fueling tube into the tank, but if the car flips over and gas begins to flow the other direction, the ball moves to the inlet and blocks the gas from escaping or the butterfly flap close
Link to this particular tab on the website How to Siphon Articles and Blog - Gas Tapper
In all honesty, I have no idea if the obstruction I encountered was a check valve, a roll over valve or simply a baffle. I did find enough tips there on how to bypass whatever it was and haven't pursued it further.
I do appreciate your assumption that I'm too young to know the difference between leaded and unleaded gas nozzles or recall the introduction of catalytic converters but I pumped enough gas and turned enough wrenches while working at service stations and garages to put myself through college so feel reasonably competent in such matters; at least on vehicles with carbs and points. Good to know I'd pass your quiz.
I suggested a siphon because I've successfully used one in the past to obtain gas for my generator
and I provided that link because it gives detail on siphoning products and techniques and lists vehicles known to work and not work with their product. Much more info there than I felt necessary to include in my response. Heck, I have no idea if the original poster would even consider this a viable solution.