Running the MGB engine without a thermostat or substitute flow restrictor
effectively reduces the water pressure inside the engine block. The fluid
flow restriction provided by the thermostat increases the coolant pressure
internally resulting in a more uniform flow of coolant throughout the entire
engine. Without a thermostat, the coolant flows very fast through the front
of the engine. This causes the upper rear of the engine to be starved for
fresh coolant where it eventually overheats. The resulting temperature
difference across the engine will create havoc on the head gasket and maybe
even crack the cyclinder head.
Just an educated guess.
Rich
1970 MGB
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