I have this 300se, it was plugged by these rad leak. Anyways had flushed (couple of times ) it with water hose from the engine block out the tube going to the water pump.
The water drained well.
When I hook the system back still no heat. Fyunny enuf when I stopped the engine say go into a store. When I came back to start the car, the heat will come on strong for few mins then cool off.
I suspect the hot water do fill the heater core, when engine starts running it somehow stops the flow.
The monojet valve ( power ) is not connected, so that can be rule out.
What to suggest from the best & brightest.
I dont wanna to change the core yet, as its as much an undertaking as changing the engine, it could be worse too, as it has the a/c cooling coil.

TIA

__________________

It sounds like a classic case of not getting all the air out of your cooling system.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I am going to open up the monojet valve to see if its toast too.

Usually air gets friven out after u drive her for a bit, I can feel the hoses hot too.

__________________