Ihave an 01 Civic EX - vtec - 5 spd
I just bought it used 90k miles on it. It runs great the only problem I am having with it is that when i am driving the heat (sometimes takes forever to get warm) will just get cold. A minute later the temperature will start to rise. It will get to to about 3/4 up the heat gague...then cool back down to about half. It normally runs a little over 1/4 on the heat gague. I took it back to where I just bought it, the Honda place flushed the radiator...and put new thermostat in it...but no go still same problem. Driving along, heat goes cold...temp goes up. Any suggestions. I have had it in the shop 3 days and thats the best they could come up with. Also when the heat starts to get warm...the car will cool back down to its normal position usually. The top hose on the engine is hot...but the bottom hose is cool...any ideas?

 

It sounds like coolant flow is intermittently obstructed, either by a stuck-closed thermostat or debris/foreign object in the system. If these possibilities are ruled out, then you should consider that the water pump may be faulty.

 

Change the thermostat, sounds like it getting stuck.