The "agent used to preserve the engine while it is in storage" is typically MIL-PRF-6081 (Formerly MIL-L-6081), lubricating oil, jet engine, Grade 1010. While the engine is running at IDLE during it's final run prior to storage, the fuel supply is turned off while the 1010 oil supply is turned on. After the engine has run on the 1010 oil for the specified amount of time it is shut-down. From this point on the engine is considered "pickled" or preserved.