I have experienced this same thing right after I wash the car and water is on the radiator. As the car heats up in that area the moisture is simply being evaporated off and due to the amount of air that comes across the nose and through the top vents, it will appear a a slight white color (almost like a small amount of fog) and it simply moves across the windshield, fogging up a little and then evaporates as quickly as it came. After that initial burn of of the excess moisture it's fine. There is no odor, no mechanical effects, and only happens when it's been washed or in some heavy rain, and only does it as it warms up. Hope that helps