This may have been answered before I dunno...Maybe not with how I am experiencing. I just changed my radiator and I was trying to bleed the cooling system, but I'm not sure if it's working or if I am doing it right. I jacked up the driver's side to make the radiator cap a little higher to ensure it's the highest point. I removed the cap and started my engine and let it run. It has some very very little bubbles, but I'm not sure if it's from air or from vibrations. I have a 180* thermostat too and I don't think it maybe opening at 180* or maybe the temp hasn't reached 180* yet....I dunno. Well anyway, I run the engine until it reaches half way and don't notice any coolant being sucked down or and bigger bubbles bleeding out. I notice nothing but a lot of very very tiny bubbles, which look like it's coming from maybe heat/vibration and I also notice steam. Maybe I'm not doing this thing right or my thermostat isn't working but then again....I dunno.I don't want to run it really any higher than half way on the temp gauge, because I get a little paranoid.