Temperature sensor

[1fastredsc]

Hello,

I'm trying to sort out a strange hot running engine issue. It started some time ago and i tried the following: replacing the radiator, water pump, and thermostat. However it still runs at 98C constantly, and sometimes drops to 95 if i turn on the heater (doesn't matter if it's 90 or 40 degrees F outside, still the same temperature). Today i tried to eliminate the possibility of a bad temperature sensor by disconnecting it to see if the connection was corroded or poor, and noticed that there are two temperature sensors that look identical in the head. By process of elimination i found that the sensor in the middle of the head is the one connected to the gauge, and the sensor near the front of the head i don't know what it does. I then tried to connect the wire for the gauge to the other sensor to see what the gauge reads (someone suggested that on another thread) and it read 40C where the middle sensor read 100C on an engine that was just running. So now i'm wondering the following, first are both sensors the same part, what does the front one do, and does it sound like i need to replace the sensors?

One more thing, i replaced the thermostat with an 80C Behr unit, the expansion tank cap seems fine since i'm not losing any coolant, and i burped the system when i refilled with coolant by squeezing on the upper radiator hose a few times and refilling.

Thanks