I have a 2016 Kia Sorento that I just bought a few days ago and it has around 43k miles and I noticed that when you turn it on and only when you turn it on it has tiny little air bubbles that come up real slow for a for like 30 seconds then stop also I filled the overflow up with water to a little bit above the full line and drove it for about 6 hours and checked it and it’s now in the middle of full and low. I don’t know if this is bad or what. Also it’s throwing a cam shaft sensor code but it’s been replaced before.
Where are you seeing these bubbles? The coolant overflow bottle? How can you see this from the driver’s seat when you turn on (I assume you mean start the engine) the car?
Are you having to add coolant? How much and how often?