Ah you know what? I think my username has configured itself to mobile version because I logged on via mobile yesterday (when I was stranded and engine overheating so I decided to pass time with this thread but then cbf cos mobile screen too small).
Anyways after getting advice from good ol' IDB, I warmed up the car by idling up to normal operating temp, then purged any remaining air by opening the bleed taps. Also made sure my engine fan was working properly. Radiator was still cold but it wasn't overheating so I took it for a spin, expecting it to overheat as usual. It did of course,  pulled over and waited around 2-3 minutes and drove around again. Temps stabilised and radiator was warming up. It's labour intensive (for me) but changing the thermostat to genuine is probably the last straw. If that doesn't work then I'm selling the car.
Cheers
P.S Kidding but my dad might lol

Is that 7-8l your putting in?

Ive just read your last post properly and it seams its fine now?
If the car is over heating sitting for 2-3min is not going to do anything. The water temp actually goes up when you turn the car off due to heat soak
 
I would not expect changing to a genuine thermostat will make make any difference except for reliability. 

The last time I got a new genuine Toyota thermostat it had the perimeter gasket included in the box.
Maybe you have to buy a thermostat to get the gasket, lol.
 

another victim of the most complicated cooling system in the world... LOL :P
radiator blocked up maybe?

Ah ok...do the thermo fans operate?? all i can think of after that is the water pump is non genuine and shagged.

are you sure the coolant isnt going into the engine???
dont mean to scare you but your pouring heaps into it but its not reaching the radiator so it must go somewhere??
ist either that or not circulating and boiling  in the block which is why yuo are getting overheating..
 
i would redarin every last drop of coolant fill it with water and make sure you have put in 13 litres atleast, then see what happens