Apart from cracked head, cracked block, blown head gasket, what causes fine bubbles in the radiator with the cap off? If anything else can cause this. I am trying to put off the inevitable, ie replace the motor? apart from the dead miss under load or at warm idle it drives ok

I told you not to put washing detergent in the radiator!:bowrofl:

either you got a cracked head a blown head gasket or a air lock.

the coolant doing its job , it must be recent and at the correct percentage needed in the system