Hey guys,

Been trying to fix a no heat condition in my 85 300D for about 2 weeks now.

Here are the things I’ve already done:
New monovalve insert (coil and plunger)
New (and higher flow) aux pump (didn’t work while bypassed either)
Flushed heater core in both directions
Tried to crack bled the return at just about every spot possible.
Thermostat also seems to be working as intended
Neither the inlet or return heater lines seem to get hot



Potentially relevant symptom, system seems to not build pressure despite no visible leaks.
It also appears to me that the check valve in the lower housing of the mini valve is allowing flow in both directions.

Despite verifying flow after the monovalve by disconnecting the soft line just before the aux pump, it seems that the heater core just refuses to bleed it’s air.