So i go to fill my car up with gas and the car is completely empty and it gets to about 8 gallons and once it hits that mark it start to overflow out the bottom of my car I’ve never had this issue before can anyone explain what it could be?

 

Sounds like you have a punctured tank or a rust leak. The fuel pump and fill neck all plug in at the top of the tank, so it would normally take a lot more than 8 gallons before you would overflow (assuming a bad seal). Best to get under the car and inspect things. I've never heard of a major fuel tank leak on a 350Z, so I suspect you ran over something (puncture), got vandalized, or have a rusted out tank.
-Icer

 

There are a million threads like this. Track your mileage and mpg. Your fuel sender is likely reading incorrectly and when you thought you were on E, you still had 12 gallons in the tank. Track mileage for a few tanks, and then just use the trip meter as your fuel gauge. A bottle of techron in the tank can help the fuel sender read correctly, but fixing this normally it involves going in through the glovebox and replacing the sending unit.

 

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