The past couple of days i've noticed that when i take it to the upper rpm range the temp gauge will peg to the cold mark, then when i shift it goes back to normal operating temp, same thing when i rev to the top of the next gear.
I have blead the coolant sytem a couple of times but no luck with that fixing it. I recently removed the IACV to clean it, i thought that might have let some air get in or something. I'm stupmed, tried searching but no luck finding anything.

backgroundon car its a 00 gsr with a 99 jdm itr swap. No overheating issues has a mishimoto dual core rad and a 12" slim fan. I've been noticing "whurring"( the best word i can think of to describe it) from the t-belt waterpump area but notice no leaks on the waterpump. I recently replaced the thermostat and it cleared up for a couple of weeks but then i started noticing it flucutating again a couple of days ago. I would say 7500 rpm it pegs cold then i run to redline and shift then it goes back to normal operating temp. The gauge goes all the way to cold very fast and goes back to operating temp very fast, almost too fast for me to think its mechanical.

I checked the ect sensor and connection but i did not see any visible problems, i have a spare so i may swap it in to see if that clears it up.