This is a bit of information which has been doing the rounds for years. I do not know where it has come from but I believe it is utter nonsense. For starters, exothermic reactions are hardly unusual, there are numerous such reactions when cleaning a car. If the reaction is exothermic, it will have nothing to do with the paint type, the reaction is with the iron - it will do the same thing on all paint, the only difference would be how the paint reacts to the heat. Now, the most important part... have you ever physically noticed a rise in temperature when you use iron-X? Do you notice the panels steaming as the water in the product evaporates away unnaturally?! No, because it doesn't happen. In fact, within the limits of what I can measure, there is no increase in temperature.
So put this into perspective. At best, there would be a fraction of a degree increase in temperature. If this is enough to release the iron, then why is the iron there at all? If you wash the car with hot water, you will raise the temperature by much much more, the paint will expand much more, so why doesn't that release the iron? When you leave your car in the sunlight or heat of the day, the panels can get so hot that you can barely touch them. So, if a bit of heat and paint swelling leads to iron release, why doesn't the iron just fall out?
A clarification on how these products work. It is NOT due to swelling! There is a complex reaction (that is the chemical terminology) where the active ingredient literally acts like a magnet for the fallout. The ingredient sticks to the fallout, once it has reacted, the fallout becomes water soluble and the complex of active ingredient and fallout becomes purple (and literally washes away). The next molecule of active comes along and the process repeats until either the active is used up or the fallout is totally dissolved. There is no swelling going on.
