Heater in 2012 F150
 

Hello, my truck heater has been acting up this winter. This last week the highs have been in the low teens so it is COLD! I seem to be losing antifreeze, I dont see any obvious leaks. The heater works when Im giving it gas, for example driving up hills and through town, but does NOT work when going down hill and mainly using just the break. Is this probably just leak somewhere that Im not seeing? Has that happened to anybody else? It is definitely either leaking, or using a bunch of antifreeze. Thank you.