High lead solder coupons are frequently tested in ASTM D 1384-87 and D 2570-91 tests to determine the corrosion protection provided by engine coolants. In contrast to 70/30 solder, high lead solder is often observed to show relatively high corrosion rates in D 1384-87 testing. Surprisingly, the high lead solder corrosion rates tend to be lower in the D 2570-91 test, despite the longer duration of this test.The basis of this effect has been investigated in different coolant formulations and in both ethylene glycol and propylene glycol. The corrosion of high lead solder was found to be directly related to the presence of oxygen in the D 1384-87 test. Replacement of the air purge with a nitrogen purge significantly reduced the corrosion rate of high lead solder in inhibited coolants. These results are interpreted in terms of the solder composition.