Difficulty with new cooling system parts

Hi,

Customer had a coolant leak, turned out to be the crossover pipe underneath the intake. They went ahead and decided to also replace the water pump, thermostat, and junction tube from the water pump to under the intake. The truck had the wrong coolant in it, some rust and corrosion in the passages led to the disintegration of the crossover pipe inlet.

Now, it seems like either the system is either clogged or can't be bled. Apparently there's a special procedure to bleed:

- Fill up the bleeder valve on the crossover pipe.
- Start engine and crack the bleeder valves on the overflow tank and at the heater core.

Unfortunately it just won't bleed. Can't leave the overflow tank cap off because the coolant will just rise and flow out of it. Upper rad hose gets really tight. When running I'm not getting heat and when the radiator fan kicks on the temperature on the dash will jump to hot and we're back to square one. However, when it sits for a while to cool down we can top it off with more coolant, but no it is not leaking again.