[f16n]

I have a 427 fe 1963 stroked with 428 crank,csr electric water pump,180 degree thermostat,1 puller fan and 2 pusher fans.When I start the car and start driving it seems to do fine but about 4 to 6 miles down the road the temp. will climb to 230 to 240 quickly and then drop suddenly back to normal.It won't act up till I try it next day after engine has cooled.any thoughts? Thanks