Is it up or down?

Saturday night our gas light came on as we were coming home from my parent's house. I told Emily we were going to fill up our van. On the way home we got into a discussion that really confused me. She asked, "When we get home is our van going to be up, or down?" I said I didn't understand and she said "Our wheels are they going to be Up, or Down? I was still confused until a moment later I remembered that I had told her we were filling up our car. I asked if that was what she was talking about and she said "Yeah, when is our van going to be up in the sky?" :) It took a little bit of explaining to let her know that filling up a car is just an expression about putting gas in the car.