The Mastercool 43710 Combustion Gas Leak Tester Kit offers a fast, economical and accurate method to test for combustion gas leaks from a head gasket, cylinder head or engine block. The kit includes an expansion tank adapter, allowing the end user to securely attach adapters to a radiator or expansion tank when performing a combustion gas leak test. The quick connect coupler will attach to the radiator cap and expansion tank adapters in Mastercool Radiator Test Kits (models 43300, 43301, 43302, 43305 and 43306, all sold separately). The test cap adapter will provide a leak-free secure connection to ensure the correct testing of the cooling system without the use of a rubber cone.