Whenever I have to refill cooling system from scratch it takes several days to get it working properly... I firstly fill via catch tank with bleed bolt removed from top of block... engine gets hot but radiator does not... let car cool down overnight... add maybe 1.5litres,,, repeat process... add more fluid...temp goes up & down making ghastly gowning & 'bubbling' sounds... maybe do this 3-4 times before cooling system fluid is stable.... clearly I'm not doing this right.... Any suggestions ?

 

Your refill procedure is entirely wrong. See attached.

 

I use a modified funnel which is like this and I find it quicker to fill also I don't have any overheating problem using this funnel.

 

I used to stand there and raise the funnel a bit every once in a while to let it vent til one day I threw my funnel and it chipped off a piece, (like the cut piece on Yamae's funnel) after that, it worked perfect just leaving that funnel all the way in.

 

I ended up removing the top radiator hose... filling both radiator & motor.... topped it up using a funnel in the bleed bolt hole.... warmed it up... let it cool down then added a bit to the catch tank.... all good now....