I think the level in the resevoir changes as the engine heats up and cools down. I don't think you have anything to worry about if your car didn't overheat and the resevoir wasn't bone dry. I just changed the coolant in my car with Prestone. I think it's OK not to use the Honda stuff as long as the stuff you use says it's suitable for aluminum engines. However, I don't know about mixing the orange coolant with the green coolant that came with your car. I htink you should use one or the other, not both.