Bare metal, especially aluminum, is an excellent heat conductor.
Just called Reliable Radiator and they said painting the tanks would be fine, but didn't recommend painting the core.
Hmmmm. One makes theirs black, one says don't paint it. Seems most used to be painted, most now are not.
Why is all that?
Well, I can think of one really good reason to NOT paint your radiator. Most of us, being amateurs, might clog it up with paint. Never mind what heat transfer difference there might be between black and silver, clogged air passages are a big problem.
But what about that heat transfer difference between black and silver? Is there a difference, and if so, which is better?
Black is better. There's no question. Turns out if something absorbs heat well, it also
emits heat well. Whether it's absorbing radiant heat or
emitting radiant heat, black is far more effective than silver.
That's why the SR-71 is black. It's not for stealth, like a night bomber. It's to help reduce the heat buildup on the skin of the plane. At the speeds that thing flies, the air friction heats the skin to 900+ degrees. Without the black paint, it is estimated that the skin would reach 1,000 degrees. Plus, once it lands, it cools down much more quickly than bare aluminum would.
So why are most radiators these days NOT painted black?
Cost.
That's it. It's
not because bare is better. It's purely to save a few pennies on each vehicle. It's actually cheaper to build the radiator just a bit bigger, than to paint it black. It's not just the cost of the paint itself, it's another series of steps in the process.
When I have to replace mine, whatever I put in it, I'll leave mine the way it comes. I'd probably clog it up if I tried to paint it.
