Just noticed my 97 C230 overheating. No warning indicators came on like low coolant or noticed any leaking. Just started driving it the other day and I noticed the gauge moving up than usual. I really started worrying when it hit almost the highest point of the gauge. At that point I stopped the car and let it cool for awhile. Drove back home with the same readings. What would be the most common problem causing this so that I can check it out before going deeper?

Forgot the add that once I seen the need pass the 120 mark, I noticed steam coming out from the engine area. thats when I stopped the car.