95 3.1 temp problems

i bought this achieva about three years ago the first winter i had it the temp gave me the first problem turned out to be the water pump got that changed. secong winter came along and my head gaskets were fryed changed those. now this winter my rad was cracked so i changed that, worked fine for a bit but then my heat started goin so i thought it might be my thermostat so i changed it and it worked good for a bit but the one i put in was a 185 now do i need a 195?. thats not all ...now the temp red lines goes down to 100 and then just kinda fluctuates between the red and 100 and it happens while driving or just idling...................can anyone help me with this casue im almost outta ideas

Welcome to AF !

Sounds like air trapped in the coolaing system causing it to heat up fast then drop fast. Thier should be a bleeder valve on the back tube right above the water pump.