The cooling system is the component most commonly deferred on classic car projects and the consequences are among the most expensive in the hobby. An overheating engine can turn a sound restoration into a major engine rebuild.

The correct approach is to flush and test the system before the first drive, not after the first problem. Replace the thermostat — they're inexpensive and old thermostats can stick closed. Replace the radiator hoses and heater hoses. Inspect the water pump for weeping at the seal.

For big-block applications especially, consider an aluminum radiator. The heat rejection capability of an original radiator was calculated for an engine in factory tune. A modified engine generates more heat. The factory radiator may be period-correct but it may not be adequate.