Just being open won't make it overheat. However, thinking there is no water damage and there actually being no damage are two different things. Even when you don't see it, water and other liquids get all over.
So, what is best to do is leave the laptop open and turned off, with the battery removed as well, for a few days. Yes, I do mean days. The more water/liquid, the more days to leave it that way. It can take a long while for water (let alone other liquids) to dry up when they get into a device. Using that device to soon can cause all kinds of problems. Including over heating and fried components.
So, turn it off, unplug it, remove the battery open it up and leave it somewhere save to dry for a few days.