it is the trans cooler lines. ive had the water pump to the trans lines leaking. get both fixed Asap! another problem im starting to hear about is the manifold gaskets for our cars going bad

 

So, coolant is topped off........... no coolant leaks. Still no heat when using remote start. What can it be? Heater controls? None of the reply's above really addressed the issue of no heat if the coolant isn't low. On my 06 LTZ no heat when using the remote start and the coolant is fine. Even the temp gauge says the car is fully warmed up, but it still blows cold.

 

it is the thermostat same thing happend to mine when i first got my monte i have the same gen as you replace the thermostat. when it gets stuck open it will warm up normally when driving it wil give off heat do to pressure from the engine. when at idel it will push out cold air. if it does it again after you replace the thermostat i would do a thero flush on the system do to a air pocket