if your rad is blocked that's going to hurt your temps, clean that and get an aftermarket chip. I suggest mark haibeck at
www.zr1specialist.com. as for the by pass valve, over 5800 rpm the rad can't handle the flow of coolant so it bypasses the rad and goes back into the block causing temp to go up. Found this out the hard way, I was playing around in second gear one day, looked down and almost **** my pants. If you swap the rad for an aftermarket one you can get rid of this "feature"