Method of testing for leaks in a closed fluid filled system and system tested by such method

In a method of testing for leaks in a closed fluid filled system that has a part thereof that expands outwardly from an at rest position that occurs when said system is sensing a temperature at or below an at rest temperature to various certain expanded positions in relation to various certain higher temperatures sensed thereby than said at rest temperature, the improvement comprising the step of disposing said system in a chamber that has a temperature below said at rest temperature, disposing a fluid in said chamber under a pressure that is greater than atmospheric pressure so that if at least one leak path of a certain size or larger exists in said system from the exterior thereof to the interior thereof a certain amount of said fluid of said chamber will be forced through said at least one leak path to change the fluid condition in said closed volume of said system, removing said system from said chamber after a certain time period, then subjecting said system to room pressure and temperature so that said part of said system will be in an adverse expanded position beyond its normal position for that said room pressure and temperature if said at least one leak path of at least said certain size existed, and then detecting said adverse expanded position of said part of said system, the step of disposing a fluid in said chamber under a pressure that is greater than atmospheric pressure comprising the step of disposing a fluid in said chamber that is under many atmospheres of pressure, said fluid in said system before testing for said leaks comprising a liquid, said fluid under pressure in said chamber comprising air.