91 240sx weird overheating problem...Help...

[kuraticus]

91 240sxAll the dirty facts,

I had an aluminum radiator with electric fans being shipped. the day it came i filled up with bad gas (i think) because i had some detonation that went away when i put actane boost in it. that night i installed my new radiator. and since then it will drive for about 4-8 miles at regular temp. then overheat. I changed the thermostat, water pump, and burped it properly. also no oil in fluid and no fluid in oil, no white or watery exhaust...when the thermostat is out it doesnt overheat at all. actually! it stays quite cold even with fans off. but as soon as thermostat goes back in i get fizzy bubbles out the bleeder non-stop....help