Corrosion protection by a commercial phenolic epoxy coating for carbon steel panels was examined after exposure to a thermal cycling regimen of 22 °C and 120 °C for 40 d. The panels, along with freshly coated samples, were tested and immersed in solutions with 3.5 and 5 wt.% NaCl at 80 °C for 60 d. Some of the samples were also exposed to water condensation. Coating behaviour was investigated by visual observation (degree of blistering and evaluation of degradation) of coating, and electrochemical impedance spectroscopy (EIS). The EIS results, and the degree of blistering and delamination around the scribed regions of the panels suggested that 3.5 wt.% NaCl caused greater degradation than did 5 wt.% NaCl. Thermal exposure improved corrosion protection as evidenced by the higher impedance (>0.1 GΩ cm2) of the specimens, the absence of blisters on the panel surfaces and the reduced delamination around the scribe areas of the thermal cycling panels compared with the freshly coated samples. The results showed that the organic coating exposed to heat exhibited an improved resistance against severe marine conditions.