Might have blown a head gasket and what you're seeing is oil mixed with the coolant. Also you might have had a leak between the upper coolant radiator and the lower transmission cooler, so if the foam was sort of pinkish that could be transmission fluid.
Also maybe it's just years of gunk in there that clogged the radiator. Probably you need to have the radiator cleaned out thoroughly and the thermostat check and if that doesn't cure the overheat you should have the new coolant tested for presence of combustion gases.
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Also maybe it's just years of gunk in there that clogged the radiator. Probably you need to have the radiator cleaned out thoroughly and the thermostat check and if that doesn't cure the overheat you should have the new coolant tested for presence of combustion gases.