I've got an 84' 380sl. Problem is that when at idle, heater seems to work at least partially, yet when I start moving, it quickly stops providing heat. Is this a valve or pump issue? The car had AC removed when I got it; the fan and defroster work fine (I know the defrost is electrical). How should I proceed in troubleshooting this? Many thanks in advance for any input.
JEFF

could be from plugged heater core, low coolant or control issues.

tom w

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[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.

What is the best way to check the heater core? Also, which direction is the flow of coolant, looking at the engine from the grill. I assume it would enter the core from the passenger side since that is where the pump is...? Do I need to drain the system to check for blockage in the core? Many thanks, Jeff