GM Bus 4104 Whistle Stop Fuel Guage.

This 1956 GM 4104 Bus has a whistle to let you know when the fuel tank is almost full.
1. Use the dipstick like checking the oil on the fuel tank.
2. Fill tank full speed.
3. When the whistle starts it will gain with intensity and then suddenly stop.
4. When the whistle stops, stop fueling as the fuel tank is now full to the proper level and has proper expansion room.
5. Flip the door closed and toggle latch and continue on your drive! Drive and repeat in 800 miles.