[iCONICA (OP)]

Hi,

Not your usual question on here, but I'm a keen reader of these forums, and it's a question I'm not convinced your average mechanic would know the answer to.

I need to replace my entire exhaust system, as my current one has corroded badly. As they're hard to obtain for my car, I want to completely protect the new one from moisture with paint.

My question is, should I use black or silver paint?

I know that black absorbs heat/light radiation, whereas silver reflects it, but what about when the object itself is radiating the heat? Ideally, it wouldn't affect the exhausts heat radiation properties at all, but I can choose from black and silver, would black paint cause the pipes to radiate more heat, or to hold it in?

Any advice would be much appreciated.

Thanks.

[yor_on]

Black is a very manly color, be a man

If it is a exhaust pipe, then it is gases coming. So what absorbs the heat from those gases best, a mirrored pipe or something in black? Then again, there might be gasoline in those gases too perhaps, and do you really want the exhaust pipe as hot as possible if so?

Thinking of it, it's a female favorite too
Black.

[RD]

Which ever colour it would have to be special heat-resistant paint.

[the colour sounds like an academic point as the exhaust on the underside of the car is going to become filthy anyway]. 

[Bored chemist]

Black will do the best job of radiating heat.
Good absorbers are also good emitters.
http://en.wikipedia.org/wiki/Kirchhoff's_law_of_thermal_radiation

But what you really need is paint that stays on the metalwork, so heat resistance is more important.

[peppercorn]

Assuming the exhaust doesn't quickly get covered in muck, is throwing off as much heat as possible really the best idea?  All this is very dependant of engine design, driving style and the path the exhaust takes under the car; theoretically, painting the exhaust black for example, could increase back pressure in the pipe (changing performance characteristics) and in extreme scenarios could even singe the carpets in the cabin, or cause fire (okay, a little extreme, but sticking to a stock system is almost certainly best all round - esp. if the car is stock in all other respects).

[CliffordK]

You may want the exhaust to remain hot until it gets to the catalytic converter (which often have extra heat shields).

A mirrored surface would reabsorb less heat than a black surface, although, that may not be a major component of the heating.  Black on the inside would absorb more radiative heat.

Stainless is sometimes used in exhaust systems, but often are discolored by the heat, so a dark color may not discolor as much.

[iCONICA (OP)]

Hi, Everyone.

I know it'll have to be high temp paint.

I'm not after cosmetics here, it's the exhaust. I just want to keep it functional for years, it's quite a rare little and parts are becoming harder to source.

I also don't want the pipes to emit any more heat than the currently do, I'm just after protecting it from moisture, and then rust.

So if I painted them in silver paint, it'd be better than black paint which would turn them into "radiators"? As the pipes are silver on the outside anyway, I guess that's the best option?

The cat is right up at the manifold, so that's not an issue.

[CycleGuy]

You want your exhaust to retain as much of its heat as is possible right up to the exhaust tip. This keeps exhaust gas density lower, exhaust velocity higher, and helps the engine to scavenge better (and helps the cat to operate more efficiently for those that are mounted further back on the car). Coating the exterior of the exhaust pipe with a ceramic coating will not only protect the metal, but will accomplish the aforementioned goals. Coating the inside will do so as well, but to a greater degree.

There are several companies doing this, but only a few that can also coat the inside of the pipe.