I have a 2001 deodge neon it started to get to the top of the operating temp and when i turned the car off the overflow was boiling. but when i drive it it normally stays at the operating temp unless im in stop and go traffic, then it climbs to almost pass ideal operating temps. i shut it off and the overflow boils again.

just flushed the radiator like 4X and it was dark brown to almost clear, i added the 50/50 Coolant and so far so good but i havent went in to stop and go traffic yet so heres hoping

good luck