i have a eg civic hatch si with a d16z6 what happens is when im driving there is no pressure in the line that goes from the radiator to the head all the water from the radiator go itno the little plastic holder right next to the radiator what could this be?
blown head gasket? ( there is no water in my oil )
thermostat? not opening up ?
im really confused can anyone please tell me what this could be?

 

you might need a new radiator cap

http://www.autoupkeep.com/QAcooling.htm#Anchor-To-36789

A radiator cap has several functions. (1) It keeps the cooling system sealed from outside contaminants. (2) By keeping pressure on the cooling system, it raises the boiling point. (3) The radiator cap allows coolant to go to the expansion recovery tank when coolant gets hot, expands, and pressures increase. (4) As the system cools down, it allows coolant to return to the engine from the expansion recovery tank. A bad radiator cap can cause the engine to overheat at lower temperatures. This will cause the coolant to boil over to the expansion tank. A radiator cap that is faulty could also prevent coolant from returning to the engine. This would create a vacuum and cause the radiator hoses to collapse.

 

i would say radiator cap......check therom and hoses while u are in there!