Coolant overflow, ideas?

[Steve Tinker]

1) Replace the coolant cap.
2) Inspect the pressure relief valve for leakage (crud around the seal) replace if required.
3) Lift relief valve D ring for at least 3-4 complete heat cycles to eradicate air in system - engine to running temp & then cool down.
4) Top up with (correct) coolant mix as level will drop if air was in the system, check the level daily until stable.