While the outward appearance of the gasoline tank and radiator filler caps are the same the inside construction of the caps is different. The gasoline tank cap has a vent hole drilled in the center of the raised portion (see Fig. 520) which allows air to seep in through the six openings in the cap and prevent a vacuum forming in the tank.
Care must be exercised to see that the caps are not mixed. Should a radiator cap be installed on the gasoline tank it would cause a vacuum to form int he tank and prevent the gasoline flowing to the carburetor.