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How is a heater core "supposed" to sit?

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Dec 18, 2000
I saw a comment in another post about car heater-cores working better when sitting at a certain angle... anyone know what that angle is? Right now mine is sitting on it's face (flat) and has been doing fine, but I just connected my GeForce3 to the system and wanted to securly mount the radiator before plugging the hoses back in. If it's supposed to sit on one of its sides then are the hose nipples supposed to be on the top, bottom, or one of the sides?
It doesn't matter as long as how it sits allows plenty of air to go through it.

It just doesn't make sense as to how something that has water *pumped* through its pipes with air being *forced* over to it make it matter how it is situated...as long as you consider proper airflow and other unrelated-to-how-the-radiator-performs-by-itself things.
i think it would matter somewhat. if you mount it vertically put the inflow at the top and the output at the bottom. Not going to be a huge difference, but every little can help.
Car heater cores are much different(and better) than online radiators such as the DD cube. They have resevoirs on the sides, and TONS Of tiny little tubes that the water is forced through by high pressure. The reason for the resevoirs is it allows warmer water to rise to the top, and make more passes through the pipes before being pumped out the bottom. If you seat the radiator so that the input/output are at the same level, you negate this effect.
So which is supposed to be higher.. the input or the output... does it matter as long as they are at different levels?
The input is supposed to be lower. This is so you do not have a trickle running though. If the input is lower it fills the radiator forcing the air out the top. When the air is removed have water touching as much of the radiator as possible for better thermal transfer.