thermostat s10

check hoses going into heater core for HOT feel.

what motor?

I have a 2003 Sonoma ZR2 that needed a new O2 sensor (bank 2, sensor 1), and I finally got around to changing it today, hoping that the O2 sensor problem may be causing my engine to run cold (temperature guage has been ~180, and it used to consistently run ~220+). Something was causing false alarms this summer with the temperature guage by causing it to jump to the red zone for no particular reason. Anyway, now that I know the lack of heat (and thermostat issues(?)) was not simply caused by a burnt out O2 sensor, I am afraid to drive my truck out of town this weekend because I might get stranded at the inlaws' house.
I just read about bubbles in the cooling and/or heating system, and I do remember hearing some gurgling noises (after turning the engine off) from underneath the dash back when I used the A/C a lot. I don't think my A/C was cooling very well, and my defrost takes forever to start working.
I am somewhat hesitant to do anything regarding my antifreeze because whan I was getting ready to flush my radiator, I ran across some alarming stories about corrosion caused by the antifreeze, specified by GMC in the owners manual, which led to an internal leak in the engine and caused major damage. Have you heard any such stories? If so, are they credible, and what should I do about changing my antifreeze?

Thank you for sharing your expertise. I will donate as soon as I find a job in mechanical engineering so that I can afford to.

Sincerely,
Big Dave