What is the root cause of core plug corrosion?
Core plugs, also called freeze plugs are exposed to the engine coolant. They corrode for the same reasons anything else in the system corrodes. Most common is depleted or improperly mixed coolant. Coolant provides corrosion protection for the system, but must be properly mixed and replaced when depleted. Please see our Detailed Topic Dexcool, coolant and proper service for a lot more information on coolants and corrosion.