Given its abundant availability, ambient thermal energy harvesting has the potential to power standalone microelectronic systems. The challenge in efficiently harvesting temperature and pressure variations is the low thermal to electric conversion ability of current harvesters. Most thermal harvesters require high temperature gradients. This paper presents the design, analysis, and implementation of an energy harvesting system that effectively harnesses naturally occurring temperature variations using ethyl chloride filled mechanical bellows. A mechanical drivetrain scales the bellows displacement and a coil spring stores the potential energy. This energy is periodically released and converted into useable electric power by a DC generator. A series of mathematical models are developed and accompanying numerical analyses completed on the harvester system. For a low frequency sinusoidal temperature cycle of +/- 1 degrees C about 22 degrees C, 9.6 mW of electrical power was produced using a 1.5 V micro DC generator for a 24 h harvesting period. The power generation capacity of the proposed harvester is sufficient to indefinitely operate low power sensors and microelectronics in environments with small temperature gradients. (C) 2018 Elsevier Ltd. All rights reserved.