Excessive solder corrosion in the radiator or heater core can cause engine failure due to overheating as well as destroying the components of the cooling system. Some solders corrode more easily than others. This work investigates how solder composition affects solder corrosion. Corrosion measurements involved two engine coolants and made use of the environment of the glassware test. In the GM-6038M coolant, corrosion of lead-tin solders increased exponentially as the lead content of the solder increased from 60% to 100%. In the ASTM D-3585 coolant, corrosion was constant for solders containing 60% to 90% Pb and corrosion increased exponentially for solders containing over 90% lead. In either coolant, to reduce solder corrosion it is advisable to avoid solders containing 90% or more lead in the repair or manufacture of radiators and heater cores.Two tin-based lead-free solders were examined as well as the more common lead-tin solders. Weight-loss results show these tin solders corrode as much as Sn30A lead-tin solder in the glassware test.