A thermal ratchet system includes a ratchet housing, a ratchet mandrel, a first ratchet, and a second ratchet. The first ratchet is disposed at a position generally fixed with respect to the ratchet housing and is urgeable with respect to the ratchet mandrel in an axial direction by a change in environmental temperature in a first direction. The second ratchet is disposed at a position generally fixed with respect to the ratchet housing and is urgeable with respect to the ratchet mandrel in the axial direction by a change in environmental temperature in a second direction opposite to the first direction. At least one of the first ratchet and the second ratchet is engaged with the ratchet mandrel.