Temp Question

Ok my Cuda is running great. We are starting to get into cooler nights and I have been turning my heat on at night. Well I noticed my temp gauge is hanging out at just below the first normal temp tick mark. I have replaced the heater core and I flushed the radiator. I have no leaks that I am aware of. So my question is how low is to low and should I trust a 45 year old gauge?