Rep Power: 0

Two months ago my '99 civic (163K), would not heat up at all, even after a 30 min drive to work goin 65-80mph. Checked coolant levels, all were ok, and did a pressure test, which was fine. Water pump was replaced at 125K with the timing belt. Then decided to replace thermostat and radiator cap (gasket had some nicks in it), then replaced coolant back to proper levels and proceeded to bleed system. Thought that this had corrected the issue because the car proceeded to heat up properly ( a mm just below the squiggly line below the thermometer on the temp guage), like it always had (instead of taking 5 mins to reach this level it now took about 10 mins.) Now the car heats up after 10 mins in my driveway, and after about 25 mins of my 30 minute drive to work, the temp needle starts to climb into the thermometer, sometimes getting up near the very top of this thermometer. As I drive in the right lane to get ready to pull over so it doesn't overheat, I turn on the heat defrost on max and the temp now creeps back down to level just below the squiggly line of the thermometer. The coolant level in the overflow is exactly where it should be and I have tried to add more coolant to radiator but it is basically at or near the top every time I check. I don't see any leaks???
What now? relay switch? should I purge the entire coolant system and re-fill?

 
Rep Power: 245

A) what car? B) if it's a stock 6G D series I'd be sure your fan comes on (could be the thermal switch). C) If it's a stock B16A, you most likely did not bleed all of the air out of the system but it could also be the thermal switch that turn the fans on.

Tip: Don't let the car idle to 'warm up' ever. First off it always takes much longer than driving it mildly. Second, it's a huge waste of gas. Third, you end up with more unburnt hydrocarbons that could also contaminate the oil. If it's below zero Fahrenheit (-18C), you could let it idle UP TO 60 seconds if needed to smooth out but no more.

 
Rep Power: 0

Thanks for the response - where can I find which stock number it is?

 
Rep Power: 245

Engine code is found on the front of the engine on a smooth surface sticking out near where the transmission meets the engine. If you are in the US, then anything that isn't an Si will be D series.