PurpleHaze

I have a 1998 C230 with approx 165K on the clock. The coolant level light came on a couple of days ago, so I added coolant, the next day same thing and the check engine light came on as well. I took the car to an independant dealer yesterday and it popped a code of P0115. I also found out that my water pump locked up. So I replaced the water pump and serpentine belt and now when I start the vehicle the temp is all the way at the botton 40 degrees.
Pressure test of the cooling system passed, now the mechanic says my right cylinder #3 is misfiring and water is in my cylinder and he suspect a blown head gasket. If this is the case what code would this pop? and should i get a second opinion?