Another over heating problem..

[newbsupra]

sorry, this might have been asked but i couldnt find the info i needed and id like to tell "my story." alright, so i JUSt bought my supra.. 87 N/A. has 183,000KM on the engine. i was driving it today, the temp was always just under 1/2 of the temp gauge. so i was coming back to my friends, raced a guy. never went over 4500RPM.. beat him, then went to my friends. it was sitting there at 1/2 still.. then it goes up to just a tiny bit below the red.and it goes down to half and back up. so i shut it off, pop the hood and u can heard the radiator fluid boiling. after it sat for 15 minutes, started it up and started driving slowly home, never going over 2500rpm and the temp drops to 1/2 again. so when i get home, the bubbling, you can barely hear it and so i check the coolant. seems that the container is coated with some oil around the sides, the liquid was not thick or anything, still like water pretty much.. no sign of oil in the hoses. any ideas.. any good news? it also needs an oil change at the moment. also, my coolant resivoir is shows full, and looks like the rad is down a bit maybe not.. it could be the cap? i drove it for 2 hours before any of this.