So I just started to have this problem. I noticed that when I start my car my temp gauge is always at half. I live in Vegas and i figured this was just the heat. But its cooled off and it still starts at half everyday.

Now I have intermittent "overheating" problems. I notice that after 10 mins of driving the gauge will go up between half and 3/4 but never over that. When i am on the highway it stays just a notch above half, but city driving, well it gets interesting. At idle it will rise up to that 5/8ths level between half and 3/4 hot but when I take off, or even rev the engine the temp gauge will start to go back to half way.

Note: Yes the fans are working, the ac gets cold the heater gets hot.

could this be the temp sensor gauge? The water pump, belt and T-stat were all brand new as of 6 months ago.

 

The temp sensor is the first thing to change, they are known to fail eventually. Try disconnecting the sensor connector, and see what the gauge does. Although I haven't tried that, I would expect the gauge to read cold. Sensors are inexpensive, so that's the first step. Tip: tie a length of dental floss to the sensor's retaining clip before pulling it out, because these have a tendency to fling into the dark. Also, be sure to remove the old O-ring which will likely be stuck in the sensor receptacle.