Coolant Overflowing

Hi, I have just been running my mk1 up to make sure fans work etc, its a 1.8KR with a top fill rad as I've deleted the heater etc, it will idle for so long ok but before it gets anywhere near hot enough for fan it starts chucking coolant out from the rad cap? Has any one experienced this or have any idea how to sort it?

Is this after a coolant change? Sounds like theres a big air trap somewhere??

I don't think it's air, not this much anyway. It will idle no problem and the fan cuts in an out but as soon as you lift the revs slightly it just goes crazy and starts overflowing out of the cap.

What colour cap is it? Black ones aren't the correct relief on them. Use a blue one. 

Yep got a blue cap on it, I've just run it up without the thermostat in too and still the same.

Have you had it running properly with the rad In before? Is it a new rad or used? You deleted anything but the header? Heater matrix?? 

Something's not operating right and causing pressure issues. 

No not had it running properly without coolant issues before, it's a KR with twin 40s it needed setting up so aldon automotive did that but I've spoken to them today and they said they had no issues with coolant but didn't have it running for a massive amount of time. 

Yeah I have deleted the header tank and the heater system.

It was a new water pump, new rad and cap also