I went to the gas station this moring (-9 out) the heater didnt work and it heated up about 3/4 of the way on the gauge. Got to the gas station saw some anti freeze on the ground and on the way home it ran cold and has been since. I replaced the radiator 6 months ago, tested the antifreeze, its good for -10.
my guess is the thermostat but let me know what you think
thank you

 

Welcome to the forum!

Sounds like a leak needs to be located & repaired first. If/when the cooling system gets low on coolant, the heater core is the first thing that is starved for coolant. This will cause low or no heat in the cabin. Temp gauge needs to be 200F. A low reading could very well be a faulty thermostat.