Is it normal for your coolant reservoir to be steaming

What is your question?

I drove my car too work 12 miles uphill. When I got to work I checked my coolant reservoir because I noticed the temperature gauge was below normal. When I opened the cap a little steam came out like a hot cup of coffee on a cold day. I added some coolant to the reservoir the next day I checked again there was more steam but the temperature gauge was normal. Should I be worried about this?

What makes this problem better or worse?

Warm days drives uphill

How long has your 2007 Subaru Forester had this problem?

One week