Temp. sending unit question. My temperature gauge is reading hot after about 5 minutes. It is not pegged out, but almost. I have checked the temp. of the coolant with a laser and it is holding about 160-170. I have replaced the gauge and sending units with new ones (several times) and checked the continuity of the circuit from the sending unit to the gauge and it was good. Voltage output of the gauge fluctuates from 3 to 6 volts and the fuel gauge reads normal. I also grounded the wire at the sending unit and the gauge immediately pegged out hot. I have the small thread sending unit. If I used the one with larger threaded base, would it read differently? I am not sure if the head is a 62 or a later one. The problem appears to be with the sending unit. Any suggestions would be appreciated.