Well, I think I've finally got the dreaded BHG. I have an 86.5 NA Supra, 138,000mi, and a few weeks ago it started overheating, and every time I saw the temp guage rise I would pull over and let it sit for a while. I replaced the thermostat, radiator cap, and then the radiator and it was still doing it. Then one day I was driving down a highway with no shoulder so I couldn't pull over when it started to overheat, so I just tried to make it to a place to pull over, and after a bit the temp dropped back to normal, and the temp would jump up and down every couple minutes, and after driving for a while my overflow container would be full. Then I thought it was just air trapped in my cooling system because I recently flushed my coolant, so I tried parking on a hill and letting it run for a while, and the bubbles just won't stop coming... I just don't know what else it could be.