Dragged my 85 300SD out of an 8 year hibernation. I did some tune up stuff and took it for a shake down run. I promptly cracked the radiator so I installed a new one and flushed the system at the same time.

I now have no heat. I rebuilt the monovalve. no change.
I unplugged the monovalve. no change.

I do no suspect the CCU as I hit the buttons you can hear it working and I can adjust which vents to blow from.

I'm thinking I need to flush the heater core.
What is the best way to do this?

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'85 300SD (formerly california emissions)
'08 Chevy Tahoe
'93 Ducati 900 SS
'79 Kawasaki KZ 650
'86 Kawasaki KX 250
'88 Kawasaki KDX200
'71 Hodaka Ace 100
'72 Triumph T100R