Why is my V6 overheating

OK this ha turned into a bit of a saga, here goes. My v6 was overheating, boiling off all its coolant and loads of steam around the expansion bottle. Thought it was the filler cap so changed it. This made no difference so took the expansion bottle off to find a 5-6 inch split in the side, so change it. This made no difference and I noticed the radiator was leaking a little so changed it. No difference just finished replacing the thermostat and again it's made no difference. After each item change I've replenished and bled the system and believe the pump is running as when it's bled there is plenty of pressure behind the water flow from the bleed points. I'm out of ideas now so would really appreciate any help.

Since posting though, I've bled the system again a couple of times and got out quite a bit of air. It’s gone from just over heating to the fan coming on then going off. Just took out for a 15-20 minute run and while the low level light is back on the temp hovered around the 80 degree mark, so I think it's a case of just keep bleeding and topping up, but things are looking better.:iceslolan