Engine Cooling problem
1971 Oldsmobile 442 V8 Two Wheel Drive Automatic

I have a newly rebuilt olds 455 motor, slightly high performance.
It heats up to 200 degrees in less than 5 min.
the theromostat is a 160 degree an is opening up in probably 2 minutes.
I have a new water pump, new alum radiator, fan shroud is on, spring is in bottom hose, timming is set at 8 degrees.
With in 10 minutes sometimes as little as 6 minutes the temp is 220 degrees and climibing and I shut it down.