I purchased a set of aftermarket gauges for my 3600. They are classic instruments and look nice. The problem is the port in the head isn't pipe threads. A 3/8 npt plug just barely threads into it. I have modified a fitting to fit and put a 1/4 npt sender in the hole but it reads higher on the temperature than it is. The tech support guy at the gauge manufacture said the bushing creates a hot spot making it read high. So i was looking at the block and there is a coolant drain on drivers side of block. Would that give a better reading? It is 1/4 npt. Another thing. With the truck running there doesn't seem to be a lot of coolant flowing in the radiator. I have a new radiator and water pump and 160 thermostat. On a hot day it will still get up to 200. Is that normal?