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"But are we splitting hairs...?" NO! Notice how a black car interior is always hotter than a tan or wh`ÜÕ® rior? Or how asphalt is warmer than concrete (step on the sidewalk then step on the street, with bare feet, and you'll see :) And a Thermos(R) has a silver lining where it stores its contents. Color and reflection play important roles in heat retention/dissipation. Polishing, particularly inside combustion chambers, keeps the heat internal instead of flowing into the heads and the rest of the engine. The generated heat is, instead, carried out with the exhaust. Jim, with his physics experience, can probably explain this better, but the heat in a polished chamber also contributes to better power usage. Since the valve covers play a very important job in keep the oil cool you want the covers dull. The thin film of oil on the valve covers transfers heat from the oil to the cover then to the air. If the cover is chromed then the heat cannot easily transfer so it builds up in the cover. Since the cover is now close to, or is, the same temperature as the oil misting over it there is little to no heat transfer from the oil to the cover. So, the oil keeps its heat and gets recirculated back into the engine and the overall heat builds up. Though another topic, this is sorta why an added oil sump doesn't drop the oil temp very much (maybe a few degrees) because the oil isn't spread thin. The black cooling tin not only absorbs heat from the engine but it also radiates it into the cooling air. A substance that is a good conductor of heat absorbs and radiates well. The opposite is true for a material that is a poor conductor of heat (these tend to make good insulators). It's hard to get a definite temperature change. There are SOOOOO many conditions/variables involved. This is something you have to trust physics and us with, particularly if the engine is used in a rather hot climate (like the southern US, along the equator, etc.) as well as in built-up motors. In these situations you want to do as much as possible to remove heat from the engine so it can operate in its temperature range as controlle@K°Ž stock cooling system (air cooling flaps and oil cooler). When you have 8.0:1 compression, dual valve springs and are running hot enough to turn your pistons purple and wear down your cam to almost no lobes you'll understand how damaging and expensive excess heat can be. Ask me how I know... :( Just like trying to get more power out of an engine by tweaking several little things to get a final hp result that's bigger, the same goes for reducing the heat -- it's additive. Toby Erkson air_cooled_nut@pobox.com <-- Please use this address for email '72 VW Squareback 1.6L bored and stroked to 2.0L, Berg five-speed '95 VW Jetta III GL 2.0L, P-Chipped, Jamex sport suspension Portland, Oregon, http://www.pobox.com/~toby_erkson/ >-----Original Message----- >> A black engine will run cooler than a white engine, all >other things being >> equal. > >But are we splitting hairs here with our polishing and >painting talk? How much >of a difference in degrees would you expect to achieve? ------------------------------------------------------------------- List info at http://www.vwtype3.org/list or mailto:help@vwtype3.org