For those of you who have to deal with falling ash from fires, such as the folks in Southern California right now, the most important car care tip for you could be not to let ash interact with water on your car or remain on the car for a long time. If ash and water -- even nighttime dew -- get together on your car's paint, the water reacts with the calcium, potassium, phosphorus and magnesium in ash and might result in chemical etching. It essentially has the same effect as pouring Drano on your car. And you wouldn't do that. While it's impractical to wash your car every night before putting it to bed, at least wipe it down.