Heater Core flow direction? (1 Viewer)

[SteadiCruiser]

Just realized after prepping the new core for install (all covered in foam now) that it can go back into the heater both ways ( so that either inlet could be in back).

I'm assuming it doesn't matter as the coolant will provide the flow direction but you know what they say about assuming.

Am I right that it doesn't matter? I don't recall seeing indicators.

 

[73FJ40]

It does matter.

Counter flow heating is the most efficient heat transfer. Counter flow means the coldest air contacts the coldest fluid, and the hottest air contacts the hottest fluid. This maximizes the difference in temperature between the fluid and the air throughout the heating cycle, which results in the greatest amount of heat transferred to the air, and removed from the fluid.

Because the incoming air (coldest) is fed to the top of the the heater core, you'd want the incoming (hottest) heating fluid entering the bottom of the heater core.

Also, you don't want the flow direction of the fluid to "fight" gravity. If the heater fluid entered the top of the heater core, the air trapped inside the core wants to rise, fighting the flow direction of the heater fluid. This could lead to an air-bound heater core.

 

[SteadiCruiser]

That's great info. So as to be absolutely clear (as either intake could conceivably be on top) there is no "mechanical" difference to flipping the core as long as the hot water ends up being connected to the bottom-most connector when complete.

Shown both ways here:

 

[middlecalf]

Which way is the flow flowing at the other ends (head and lower radiator hose)? Looks like out the head and into the lower radiator hose, eh? So head hose (hot) goes to bottom of heater core, and lower radiator hose goes to top of heater core. Thoughts?

 

[Skreddy]

That's great info. So as to be absolutely clear (as either intake could conceivably be on top) there is no "mechanical" difference to flipping the core as long as the hot water ends up being connected to the bottom-most connector when complete.

Shown both ways here:
View attachment 2831657

View attachment 2831658

I believe what you are saying is correct: there is no specific in or out on the heater core itself. The tubes inside are not directional.

 

[73FJ40]

Which way is the flow flowing at the other ends (head and lower radiator hose)? Looks like out the head and into the lower radiator hose, eh? So head hose (hot) goes to bottom of heater core, and lower radiator hose goes to top of heater core. Thoughts?View attachment 2831756

@middlecalf

Yes, the hot water supply to the heater(s) leaves the top of the head, should be routed to the bottom port on the front heater, and the return from the heater flows back to the bottom radiator hose.

Note that the bottom hose supplies cooled fluid from the radiator to the inlet of the water pump, under suction. (much lower pressure than the discharge of the water pump). This lower pressure draws the water out of the return hose from the heater.

 

[73FJ40]

@SteadiCruiser

That's great info. So as to be absolutely clear (as either intake could conceivably be on top) there is no "mechanical" difference to flipping the core as long as the hot water ends up being connected to the bottom-most connector when complete.

Shown both ways here:
View attachment 2831657

View attachment 2831658

Correct.

Note this is likely your first lesson in thermodynamics! (unless you've touched a hot stove or exhaust manifold!)