Hello, I am having a problem with a 1999 Grand Caravan gas leak. Problem is coming from the middle area of the gas tank only when it is freezing cold outside when the engine is running and only when the tank is above a quarter full. The leak stops the minute the engine is shut off. It actually pours out, not just a small leak. I lost almost a half tank of gas in twenty minutes the first time this happened. Need help as I am ot a mechanic and need some knowledge before I go to one.

thank you