The original plastic-tank radiator turns brown/green and grows brittle with age, failing suddenly and risking an overheat/blown head gasket; owners call it a cheap two-bolt DIY (TYC1140 equivalent, under $100) and advise replacing all coolant hoses, which fail from age not miles, at the same time.
Cooling system: plastic-tank radiator is a known weak point
Mazda MX-5 Miata (NA) · mechanical