On 1968 C10 heater core which tube comes out the top of the heater box?

[kwmech]

Originally Posted by HeavyHauler

According to the diagram above the pressure side (water pump large hose) goes to the top while the (intake manifold connection small hose) is at the bottom. The diagram pic seems the opposite of what you are saying?

Water pump hose is not pressure, it is suction or better known as return, same as in the later models running to the radiator. Pressure comes from the intake manifold after the water pump pushes water into the block