The effect of thermal cycling was carried out on steel bars (0.4 C %). A single run was performed at a lower temperature of 32℃ and an upper temperature of 500℃ cooled in water, seawater (previous results) and oil (new results). For several numbers of cycles up to 30 cycles for an accurate determination of heating and cooling times. The effect of thermal cycling on the corrosion rate was evaluated. The effect of thermal cycling on the following properties was evaluated the corrosion rate. The comparison between the effect of thermal cycling on carbon steel (0.4 C %) seawater and water-cooled (previous results as shown in references [1, 2]) and the effect of thermal cycling on carbon steel (0.4 C %) water-cooled (new results) has been studied. From the obtained test results (previous and in this paper, it was found that: the type of corrosion is uniform attack; corrosion rate of the first stage gradually increases with the number of thermal cycling up to 15 cycles, then it takes steady-state up to 30 cycles. It was found that the rate of corrosion (previous results, seawater and water-cooled) is more than the rate of corrosion of the new results, oil-cooled respectively.