No heat when cold

[632 Regal]

Heat issue 95 530. When I start the car in the cold I get no heat (obviously til it warms up). When it does warm up I get no heat at all. It blows cold. Rev it up to get circulation and no heat. If I drive it I get heat. After I do get heat it will blow hot at an idle and not cool down so the aux pump works. Coolant level is full.

[632 Regal]

Update: Pulled the heater valve from the parts car, looks to have been replaced with a new Bosch unit at one time. Pulled my current unit out, while in the process one plastic hose barb pulled out on the unit. While inspecting I noticed a crack down the side of the plastic housing. So... my old unit would drain coolant over night leaving an air cavity that would not fill until pressure and driving. New unit clicks and the pump works so I will see if it gets heat in the morning. I did not check the old unit at all.

[shogun]

Lucky that you noticed the crack early enough, one of my friends had also a crack in the plastic of the aux water pump (connection stud from aux pump to heater valves), most of the coolant lost, head gasket blown.
Coolant circuit diagram M60 engine https://imgur.com/MV1c0xr