2005 Honda Civic with gummy coolant

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?

Most likely the head gasket. 7thgen civics have poorly designed heads and the gaskets go out more than they should. Ive replaced two on both my civics.