Can anybody let me know the internal diameter of the heater matrix pipes that run from the block through the bulk head to the heater?

Thanks

Hello and i'm a newbie who has just bought a stunning Hilux Surf 2.4TD. Now i guess it's what you have all heard before so here i go.
My Hilux is in such perfect condition apart from overheating. My friend was the last owner who changed the head with a modified one, changed thermostat, radiator,...