R32 GTR Engine Temp gauge not working

[dak24]

Hi, I have a R32 Skyline GTR, and I'm having issues with my engine temp gauge not working properly. The gauge ususally reads the engine temp when the car is idling, but as soon as I start driving the car the temp gauge goes right down to cold, and sometimes it doesn't read the temp at all. I've replaced the engine temp sensor, and I've got all the air out of the system, and it's still not work. I am getting warm air through the air ducts but its not hot, so it makes me question if its the thermostat or not. Anyone having any idea what my issue could be?

[beacher1B0]

For the price and piece of mind i would change the thermostat and coolant anyways. Then go from there.