Some amateur flushed my system twice,put anti feeze, anti boil in,didnt bleed th system, henxe car heated up,heard a hissing noise when openin bonnet,no water when my son checked,but we found leaking heater tap, replaced it, filled with coolant and water, bled th system, i drove bout 80 k's, temp hot,lifted bonnet, hissing sound, coolant spray on top of radiator, used 2 litres of water, please what is wrong.but twice when gauge up, and ive turned a corner, gauge dropped.why