Anyone got a pic of this? I can't seem to locate it. I must be blind, sorry, but I looked all over near the battery and I don't see anything that could resemble this.

 

+1 I also couldn't find anything like that today when I was trying to get my bubbles out of the system

 

this may be completely different but my blazer did something similar and i flushed the heater core out took like 10 minutes and all kinds of junk came out and it fixed it. Got so hot after the flush felt like ur face was melting

 

Is the blend door vacuum operated in our cars?

 

Okay, i finally found it.

It's very close to the firewall and hidden under this big wiring harness that leads to the battery.

It has a + on the top for a philips screwdriver to unscrew with.

I'll try the bleed technique to see if that helps. I.e. unscrew the top off and let it idle while pouring coolant/distilled water in the radiator cap opening. rev to ~2,000 RPM until stuff comes out of the bleeder.

Hope it works!