Rep Power: 0

I have a 99 Civic that's overheating and trying to figure out the problem. Here are the facts:
1. Put in a new radiator because the neck was cracked and losing coolant
2. Installed new thermostat when radiator was installed
3. Not losing any coolant now
4. Most of the time turning on the heater cools it down, but not all of the time.
5. When it overheats, the thermostat needle goes up and down between normal and hot. Sometimes just stays on the hot side and sometimes fluctuates.
6. Water pump seems to be working OK
7. Fan seems to be operating properly

Puzzled in Ft Lauderdale!

Any suggestions?

 
Rep Power: 519

I'd want to see what the PCM is seeing first, using a decent scanner to read live data.
Maybe the temp gauge on the dash is lying to you.

Or maybe it's blown the head gasket.
Is the radiator staying completely full-- to the top-- at all times?