i had a similar problem,
1; my thermostat was rusted shut due to mixing 50/50 coolant and water
2; solution---, i bought a 160 degree thermostat with new seal, this thermostae opens early and keeps the open till the temp is leveled or lower
3; i emptyed out and flushed the radiator, jacked up the car in the back and purged the block, i completely washed out all the shit that was in there and when i was done i want and got some prestein all antifascist and fulled her up and from then on there she never did again, and if that dosent work and u dont have any leak, well then it might be ur head, and if it is, i wld pull that motor out and swap for a jdm 1.....