I have a 1989 Civic LX 1.5L and I was doing some work changing the thermostat only to find out that there was no original thermostat in the car. Anyhow, when I was done, I went to bleed the air out of the cooling system and while loosening the bleed screw, the piece the the bleed screw attaches to literally broke off. I do not know the name of this piece. The upper radiator hose also connects directly to this piece.

 

water outlet cover - part number 19315-PM3-000 - #6 in picture

 

Go to a junk yard and get one. Next time don't bother with the bleeder screw. Just run the engine until its nice and warm and thermostast is open with the radiator cap off.