1971 Lemans coolant boiling
Check the thermostat, might be stuck closed.
Make sure you have 50/50 coolant and water. Plain water boils at a much lower temperature. If this and Tom's advice does not work then check compression to make sure you don't have a leaking head gasket.
Also check your ignition timing. If it's retarded (late) it will cause the engine to run hot and possibly boil over when shut off. HTH. - Jim
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