Today when I got home I noticed my temp gauge at H so I opened the hood and heard sizzling it was coming from the back of the engine and smells like coolant. There's also some sizzling and bubbling of hot coolant near the front of the coolant overflow tank where it looks like someone previously sealed it with gasket sealer. Anyone know what could have gone bad. Water pump? Thermostat?

 

Pressure test the cooling system and stop driving it until you know what's wrong.

 

thermo is good and I'm assuming water pump is good since i found out i was replaced about a year ago. The steam is coming from behind the motor, are there any coolant lines running back there?