When the cooling system starts to build up pressure, ie almost immediately after starting, my radiator cap starts pissing out coolant, if I push it down and seal it better, it comes out the overflow. Could there be some sort of blockage somewhere, I've got no idea. Really wanna get this thing on the road for at least one day of MMX!

have you tried a new cap?

I'll have a go with the one off my TJ if it fits tomorrow. I suppose if it was rooted even when I push it down to seal it it might come up therough the overflow...

Its not worth the price of the petrol boss.

Hang on, your at MMX, why not ask one of the 50 people there for an opinion

Negative on the TJ one fitting. Repco it it

if its building pressure that quick (from cold?) sounds like a bigger problem at hand lol
is it loosing water/coolent? try starting it without the cap if it starts bubbling/shooting out a bottle of chemiweld might fix lol

Bit more info would be handy.....

How soon after starting does this happen? If you had cap off and let car idle and warm up, do you see nil movement of coolant in the radiator initially - then see a gradual increase in movement of coolant as thermostat opens? This would confirm a/ there is a thermostat fitted b/ the thermostat is opening, at least partially.

Looking for bubbles/oil in coolant and steam/condensation/emulsified sludge in oil filler should handle the basic queries for head gasket or cracked head.

What's the temperature guage doing throughout all this? What's the condition of the coolant, is it running coolant or water? Just wondering is the water-pump so corroded that its not circulating coolant properly?

I'm kinda assuming that if is wanting to chuck coolant out, then either the cooling system isn't shedding enuf heat - so ineffective water pump, or blocking thermostat or clogged radiator cores etc. OR possibly worse news in that combustion gasses are getting into water jacket and overheating and pressurising the coolant - so suspect head gasket or cracked head?