VWFan said:
Willys - Are you sure about the heat???
The reason I ask is because coming from the air cooled world I have always heard that the chrome parts will not dissipate the heat as well as say black parts. I am not sure if this is true, but I have always heard that. VW owners are pretty attentive to heat problems and I would think that they have tried almost everything to keep the old VW cooler, to include running tests between chrome vs. non-chrome. I'm not trying to argue, I just want to double check the info....
Technically you are right. A perfectly shiny surface would emit zero radiant heat while a perfect black body would emit gobs of radiant heat. Chrome is a very good imitation of a perfect shiny surface and the radiant emissivity is very low. However, the amount of heat radiated is also a function of the distance from the hot body to the 'cold' body to the 2nd power and of the temperature difference between the hot body and the cold body to the 4th power. None of those values is very significant in this case. That is the only heat transfer mechanism that would be affected by the chrome and anyway, a polished aluminum surface would have a similar radiant heat transfer rate so there is no benefit to either.
There are two other heat transfer mechanisms acting on a water pump - one being convective transfer of heat from the hot metal surface to the air blowing past it. That is a function primarily of the difference in surface temperature of the metal and the temperature of the air blowing past. True a smooth surface like chrome or polished aluminum transfer less heat than a rough cast surface but again, not much difference to even worry about it in any pump you might buy. The last mechanism is conductive heat transfer from a hot body to another in contact with it. Aluminum is a better conductor than iron or nickle but again, the heat transfer rate is strongly driven by difference in temperature between the hot and cold body. Since the water pump is virtually the same temperature as the engine block which is the only thing it is in contact with, nothing to worry about here either.
A nice glossy thick paint job is much more detrimental to heat transfer than a metallic chrome surface.
In summary, yes there are obviously differences in potential heat transfer rate for different water pump materials but I would bet a dollar to a donut that the difference in pump temperature at the seal, which is the only part I can imagine that would care about what the temperature is, would be quite insignificant. Heat transfer in a water pump is not a concern to automotive engineers and is insignificant in the grand scheme of things. You could perfectly insulate a water pump from it's surroundings (actually, with some of the big, close fitting water pump pulleys they put on some cars, that is in effect what is happening to some pumps) and it would last as long as one that was cooled as well as possible.
