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

[HeavyHauler]

I am getting ready to put a new heater core into my freshly restored heater box for my 1968 Chevy C10 396 big block short bed fleetside.

Which tube should be coming out of the top of the heater box and which should be at the bottom?

My truck is heater only from the factory.

In the pic I provided does the smaller outlet hose end at the top go to the intake manifold while the larger outlet hose end at the bottom of the pic go to the water pump?

[Orange Crate]

The assembly manual has this....

[PbFut]

Pressure to the bottom of the core. This forces air out the top. If you run pressure on the top you are trying to force air downward in the core and making the bleed difficult. Years vary and so do water pumps, manifolds, and radiators making the plumbing a challenge at times.

[HeavyHauler]

Originally Posted by PbFut

Pressure to the bottom of the core. This forces air out the top. If you run pressure on the top you are trying to force air downward in the core and making the bleed difficult. Years vary and so do water pumps, manifolds, and radiators making the plumbing a challenge at times.

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?

[geezer#99]

The big hose goes into the suction inlet port on the water pump.

[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

[Orange Crate]

I think the confusion might be the designation of the hoses in the text. Since the diagram is for the heater core installation the hoses are labeled as such. #1 is the INLET to the heater core and #4 is the OUTLET from the heater core. As these would be opposite labels if the diagram was referring to the water pump/block. No?

[HeavyHauler]

Originally Posted by kwmech

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

Thanks for the clarification. I installed my heater core into the box today in the same position as the pic shows and will route the hoses the same as well. The top big hose to the waterpump and the bottom small hose to the intake manifold.

[geezer#99]

Your pic shows smaller on top, bigger on bottom.
Opposite of what you need.

[HeavyHauler]

Originally Posted by geezer#99

Your pic shows smaller on top, bigger on bottom.
Opposite of what you need.

I installed it in reverse of what my pic shows. I put the larger tube on top just like the factory diagram pic has it.

[geezer#99]

Sorry!
I realized what pic you meant a little to late.