This is one of the questions i have, the other question is why does the level of water or coolant is droping when there is no external leak, no sign of sweet smell, no sign of water mixed in the oil, no milky coolant in the radiator, no bubbles, engine starts perfect it runs perfectly, no white smoke, i have a doubt that it might be the HG. And yes i am wondering why the coolant is spitting out when under boost, the spit is pretty strong about 50-60 cm. You see when the car is either cold or warm, when the engine goes to high RPM, if the cap is off it spits out the coolant but when the cap is on the coolant goes to expansion tank and it gets overfilled and the coolant out of expansion tank does not return to the radiator