2kdrift

My temp gauge in my SI cluster seems to have gone bad since my rebuild. It reads cold but after only 1 Minute of running its all the way to the H, at this point my valve cover is still somewhat warm not HOT at all. I have immediately swapped the cluster with another on ei have and it reads where it should be still very close to the C. its something with the cluster itself. Any idea how to fix this ? kind of an expensive part to replace at about 250 on ebay

thanks