Internal corrosion resistance of radiators and heaters is becoming more important as automotive manufacturers seek durability past 10 years, and as the usage of aluminum heat exchangers spreads to markets with poorly maintained engine coolant fluid from a corrosion inhibition standpoint. Simulated Service Corrosion Tests (SSCT) are used to evaluate the resistance of three aluminum alloys to tube failure in various corrosive water and depleted coolant conditions. The paper documents results from such tests that lead to two major conclusions: (1.) A weakly inhibited Oyama water solution with a silicated North American engine coolant is highly effective in ranking internal liner alloys for their pitting corrosion resistance, and (2.) AA7072 lined tubes exhibit superior pitting corrosion resistance compared to 1XXX lined tubes. Electrochemical test data obtained in a simulated pit electrolyte and the bulk test solution are utilized to develop an understanding of the SSCT results.