PURPOSE: To safely, promptly and accurately determine a specific gravity, a liquid level and a liquid state of a coolant by a method wherein a transparent cylindrical pipe provided with display means showing a specific gravity of a coolant passing through the inside of a pipe is substantially horizontally fitted in an upper side radiator hose.

CONSTITUTION: A transparent cylindrical pipe 18 is provided in a substantially horizontal portion between an upper side radiator 14 and a radiator hose 16 via an eccenric adapter 36. A pluralisy of transparent pipe-like member 28 to 38 are substantially vertically fitted along an inner wall of the cylindrical pipe 18, and float 40 to 50 made of synthetic resins which are manufactured so as to float on a coolant 56 of a predetermined specific gravity are movably housed in the members 28 to 38. By a marl 52 printed on a fine piece 53 adhered onto an outer face of the cylindrical pipe 18, an aptitudes of a specific gravity of the floats 40 to 50, namely a specific gravity of the coolant 56, and a freezing point and a liquid level can be known. Further, as the cylindrical pipe 18 is transparent, color of the coolant 56 or transparency can be examined.