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Simple 720 heater core question


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It really doesn't matter that much, like asking if a sandwich tastes better upside down.


On the engine side of the firewall the hot water from the block is the bottom hose, the top one goes to the intake and eventually to the lower rad hose inlet to the water pump.

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 You would need two shut off valves to isolate the heater if there was a leak. Water would still be supplied from the lower rad return side. When the engine is hot there is always some pressure in the cooling system


I would assume the stock set up is hot side to the valve but it will still give heat flowing in reverse..

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  • 4 weeks later...

Well dang. When my heater core started leaking, I just connected the two hoses that went to it together. They're still like that. I figured if I could do without heat in upstate NY, I could here on the Mississippi Gulf Coast. And yes, the Datsun was driven here from NY (in March). I've had no luck finding a heater core.

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You're ok for the winter but come spring either fix that heater or plug those heater hoses.Normally when it gets hot out and the heater is shut off the valve remains closed and no hot water is moving. When you connect them together the hot water from the head is recycled without cooling it right back into the engine again. If you compare the heater hose to the top rad hose about 20% of your hot water is not being cooled at all. This put a big load on the rest of the cooling system.

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