I have a 92 Bonneville SSE with a 3.8L engine (no supercharger) that has about 138K. My temp gauge used to sit at about 208 once the car warmed up. Here lately I noticed it fluctuates. It goes up to about
220 then drops to about mid scale. It rises slowly (maybe 5 mins to reach 220) then drops fairly rapidly (15 secs or so). Also, I can't sit a and let it idle (like in a dirve thru or rush hour traffic) or it just keep going up (past the 220 but I have not had the nerve to see how far it will go). Once I pull off it drop to mid scale and begin the fan effect (up and down) again. It otherwise runs well, starts easy, good power etc...I had the cooling system flushed (thinking it might be air bubble) and bought a new radiator cap (thinking the pressure was releasing too soon/late). My water pump was recently changed and I had to change my radiator (I broke the hose connection trying to get the upper hose off. Plastic?). I can hear the fans kick on but not sure how to test if they are operating normally. Any ideas where I should proceed from here?