I've tried adding coolant to the system cause it was overheating and blowing out cold air 80% of the time, And it was fine for a few days and did again. So I took the cap off and it was low so I added some. Now I'm having to add coolant pretty much every time I turn the car off. Any suggestions on what the problem might be? Or has anyone experienced this problem with their IS? And how did you fix it? Thank you in advance for any help or suggestions.