Heater issue

[jondee86]

With the water circuit shown, the flow is essentially governed by the
resistance of the heater core versus the resistance of the radiator core.
If the resistance to flow of the heater core is greater than the resistance
of the radiator, then the water will take the path of least resistance.

AFAIK most heater pipework setups use the pressure differential created
by the water pump to ensure flow through the heater core. So I think that
you will have to tap the heater return line into the high suction zone close
to the back side of the water pump.

Cheers... jondee86