Coolant leak, Heater not warm
 

I have a coolant leak that happens only after the car sits awhile. I cannot locate where it is coming from after removing the plastic shield and inspecting the engine from the bottom. It is not around the radiator nor the secondary water pump. I already did the valley pan and collapsible tube replacement. In March. Also the heater is no longer blowing hot air. I am starting to think there is an issue with the thermostat or water pump. I lose about a half gallon of coolant every 10 days

I have a 2004 4.4

Are you burning it or is it leaking onto your floor boards?

It is leaking onto the ground from around mid to rear engine but that could be due to the plastic shield on the bottom