My daughter just bought a c250 Beautiful car. Third time she cranked it

What is your question?

Message board stated low coolant, I filled with Preston 50/50 coolant. I let it set and when I cranked it, it sounded like a rattle ,then idling slow and loud, then would correct itself. I drove down the road temp was running a little warmer. Turned air off. After I parked it, I cranked it a couple of more times, started right up perfect. I looked under the car and didn't see any wetness, no leak. What is this problem? After I parked it the check engine light came on. It came with no book. Any advice would be greatly appreciated.

What makes this problem better or worse?

I add coolant, message board said low coolant. After letting it sit for a few minutes, I drove it down the road and appeared to be running warme

How long has your 2012 Mercedes-Benz C250 had this problem?

We just got the car yesyerday