The upper hose that comes from the thermostat housing is in. But in most cases it doesn't matter what way the fluid flows. Many do not have a directional check valve.
No it shouldn't. It's a heater core. Hot water in and slightly cooler water out. The only concern would be if you ran a radiator cap higher than 18psi.
No it shouldn't. It's a heater core. Hot water in and slightly cooler water out. The only concern would be if you ran a radiator cap higher than 18psi.