Water does flow in the radiator with the cap off, hence it is not a faulty thermostat or waterpump!

How can I tell if it is the head?? There are bubbles but only when the car is at running temp! No oil in water, no water in oil!

Could it be blowing out the exhaust as I have heard this can happen???

some coolant will go out the overflow as the radiator will not actually be full to the brim all the time as the liquid expands when hot, its usually 1-2cm below the lip of the cap.

Hmm so the main problem is the overheating.
1. Could be the water pump. If you can see the water flowing across the radiator with the lid off not the water pump.
2. Could be a head gasket. With the cap off look for bubbles at idle

Own a Datsun sunny, a15 with new gemini radiator, new thermostat etcc

I put new collant in it and bled the system appropriately by allowing the heaters to run to ensure I have no air pockets. It still splurts coolant out the radiator when revving the car with the cap off and running temprature! With the cap on it goes into the overflow????

What should I do, drain all the coolant and start again?? If this is not clear please ask further clarification questions! This problem has been bugging me for a while!