Overheating when I sit idle. it overheats when I sit idle.when it was overheating I was stuck in traffic.I ran my heat all the way up on high and it began to cool down.Then after a few minutes,the heat started running cool and the gauge went back up to high.It would intermittently go back and forth doing this.hot heat/cool down , cool heat -heat back up,when I got it home,it was hot, but no steam or water overflowing like you would expect.I have had the thermostat changed.the waterpump shows no leaking.TIA

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Over heating the engine is a serious concern. With the hood raised you should hear the motorized fan turn on just behind the radiator as the engine requires additional cooling.. If you look in from the rear of the radiator you should see the fan blades.

This electric powered motor operates on a thermostat and when the engine temperature rises this fan should come on. I'm assuming from your description that when driving and air is flowing through the radiator as the car travels the engine is nor overheating.

Check fan motor thermostat, check fan motor and check wiring.

Wiring Diagrams related to the Honda Civic
http://www.wiringdiagrams21.com/category/automotive/honda-automotive/civic

Motor engine cooling fan only runs as engine temperature requires additional cooling.
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