I seem to have a lot of air pressure inside my coolant lines i opened up air bleeder valve and is instant had air and steam flying out how long should i keep it open any help be great my : 2004 sebring convertible 2.7 v6

 

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The cooling system is supposed to be pressurized. The pressure cap located on the plastic reservoir maintains the pressure at about 16 psi when the engine is warmed up. Turning that bleed screw on top of the engine is a very bad idea. It screws into a metal seat that is retained in the plastic housing by tiny plastic flutes that can easily shear off due to the screw threads sticking to the seat. Then a leak develops. Keep an eye on that are for evidence of leaking.
The part the bleed screw sits in is called the coolant outlet manifold. There is a lot of discussion here in the forum about that part and how to replace it. Search the forum for the discussions.