Vfr400KM wrote:thankyou, i think the rad cap has fixed the issue. I am however worried i may just be hiding the issue or would boiling/otherwise bubbling coolant still push past the new cap?

If you have a blown head-gasket / failed waterpump a new rad-cap will not fix the issue. it will still build up enough pressure to blow the cap eventually and dump coolant to the expansion tank.

you may notice the bike running very much towards the hot if this is case... nc21/24 usually run very much towards the cold side.

the bike will bubble when hot without the rad cap on anyway as the coolant needs to be under pressure to raise the boiling point.

if its constantly bubbling from the get-go on a cold engine its probably head-gasket - waterpump issues or even a crazy amount of air in it.