help with p0118 and p0335

I got a CEL light and the coolant started builing and overflowing. I hooked up the scanner to my 98 cavalier 2.2L and get p0118 and p0335 and it looks like my Engine Fan is not running and the engine temp. thermostat is not working. I replaced the P0118 Engine Coolant Temperature (ECT) Sensor, cleared the code and started the car. The thermostat gage ran for about a min and it went back down and the CEL light came on. I scanned it and I get a p0118 code again but not a p0335 this time. Any suggestions? It's driving me nuts

:banghead:

Thanks!

try changeing the thermostat and the temp sensor foe the gauge