I seem to recall this topic coming up here some time ago. Is it a bad idea to keep pumping gas into a car when the pump shuts?
Yes, it is a bad idea
It overwhelms the vapor recovery system which is part of your emission controls. That makes a check engine light come on and will fail your state’s emissions test. Plus it will cost you a few hundred to repair.
So don’t do that.
You’re about to get schooled on that like I was. There’s a valve that stops that from happening in more modern cars.
However, it’s still a bad idea because once the tank and the filler neck is full of gas, more gas has nowhere to go so you are likely to spill fuel, which is bad for the environment and your paint job.
At the end of the day, you’re gonna get a negligible increase in driving range by doing this, so there’s simply no point.
Ray actually answered this fairly recently. It depends on how much more gas you pump. If you’re only rounding up to the next nickel it won’t do any real harm but if if you keep forcing gas into the tank then yes, for the reasons already cited.