all this shiny/polished surfaces retain/reflect heat and matt black surfaces emitt heat is only relevant to radiation of heat. intercoolers do not work on this method of transferring heat.

intercoolers use convection. the surface colour could be pink and it won't affect the way the intercooler transfers heat.

rocker covers and engine blocks on the other hand only have radiation to use to transfer heat and matt black is the go for them.

I've always been a fan of the mat black intercooler just for subtlety. Like L18_B110 said it doesn't make a bee's dick of a difference until you start putting thick layers of paint on the core and actually start insulating the compressed air inside it.

As was mentioned earlier, the colour of the surface only has an effect on radiant heat. Radiant heat is a function of some constant of radiation, the surface area and the temperature difference between the surface of the material and ambient temp. As you can imagine the surface of the intercooler will barely rise above ambient making radiation negligible.

I would like to test out a few intercoolers myths, mythbusters style, could be interesting.

Shiney surfaces retain heat. Thats why your gran would try to keep her teapot shiney, to keep her tea from cooling down too fast.
Some of chryslers engines has wrinkle black painted rocker covers. I've always found that chrome rocker covers retain heat to the point that the valve guide seals will bake hard in only 6-9 months.

My personal opinion is that radiators were originally painted black because they were made from copper, and copper goes ugly very fast when exposed to moisture and air. It was probably also for looks, as you get that "empty" look when you can't see the radiator/intercooler. Lately I can't remember when last I saw any new car with a raiator/intercooler that's been painted black.

Think about aluminium foil that you use when cooking, it's got a shiny side, and a matt finiish side, depending on what you are cooking, mostly you will use the matt side towards the food, so that the direct heat from the heat source is reflected away by the shiny side, and you don't get food that's burnt on the outside, but raw on the inside. So if even that slight difference in colour can make a difference, just think what black would do, it would attract more heat even just standing in the sun.

Keep it shiny, looks better anyway...

Most radiators,coolers etc. are painted by the factory for a good look factor and also to help protect the cores from the OUTSIDE elements in a daily use situation.

Black is used as it covers a multitude of minor inperfections,is cheap and covers very well.

Ask yourself one question:How many competition vehicles have i seen with painted (aluminium) radiators,oil,water or air?

doesn't matter at all.

air-air intercoolers work by convection on either side of the intercooler surfaces and conduction through the material.

the surface coulour will only effect radiation properties of the surface.

however a thick coating of paint could decrease efficiency by acting as an insulator.

shiny stuff refects light, and will probably also reflect more heat....so if your worried about the heat from the outside polished is good

and if you paint it then the heat will have to be transfered through the paint also....so less stuff on the outside of the cooler the better

mercedes coolers are left unpainted from factory im pretty sure(vito ones definatly are)
and i think the XR6 turbos may also be unpainted

id only worry about painting the cooler black if i was trying to hide it

but factory has always painted radiators in black/matt black for the best radiant heat, ie it radiates heat greatest. that is what i was always taught

....but black absorbs heat

heres some theory >when i built my computer. I linished and buffed the surface of my alloy heat sink for my cpu .this gave a greater heat transfer across the face of the heat sink thus having a better transfer of heat.....................
If i were a black t shirt in the sun my body heat will be geater than wearing a white one ...........
So polishing the inter cooler would be the best option ............