radiator shows gummy coolant. what is causing it
Gummy how? Oily gummy? Possibly failing head gasket.
Have you ever tried to fix a radiator leak with some form of “stop leak” product? Have you always owned this car? If stop leak has been poured in it makes a huge mess in the coolant and it is tough if not impossible to flush out.
How many miles on it? Have you had it checked for a failing head gasket?