Rep Power: 0

I have a 2004 Civic Ex Coupe AT and when I drove it a long distance, about 150 miles, about 95% through the way back the gauge started to go all the way up to the H and stayed there and the car was running really hot. I haven't driven it since (couple days ago), today I ran the motor and gauge sits slightly below half way. Not all that great with car knowledge, my friend said it's not the fans as they were running when we turned the AC on but perhaps a sensor or maybe the thermostat. If anyone has any idea any help would greatly be appreciated. I can try to list as many details as you require.

 
Rep Power: 192

Did you check the coolant level? Not only the overflow tank but the radiator itself. Be sure the engine is cool before you pop off the radiator cap, coolant should be up to the neck.

 
Rep Power: 185

We'll go through the usual steps here. Do what anibis said. Check specifically if the overflow is filled to the top. Also, if you remove the rad cap and there's no coolant....wait for it....blown head gasket most likely. I would do a search for blown head gaskets and read the thread at the top of the mechanical forum about over heating and common causes. Not always, but the most common cause, if coolant levels have been maintained correctly, is a blown head gasket in these cars. Not what you wanted to hear, but reality. Good luck with whatever you find.

 
Rep Power: 199

If it overheats at all the resevoir fills. Yes the HG is byfar the most common, but I have put a radiator fan switch on mine, it also did an HG job on it too, but besides my point.

 
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It's really sucking down coolant as well. It doesn't overheat unless you drive it on the freeway for at least 30+ minutes and then get off the freeway. Mechanic said it is most likely the HG. Anyone think it could be anything else?

 
Rep Power: 199

Sure it could, the Sun, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto could've aligned and that the reason .

AJA though see what the mechanic would charge you for a definitive diagnosis, not just an I bet. This is an engine, not physics, they should be able to extend that courtesy....

 
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The mechanic didn't actually look at the head, he just said he use to have a civic the same year and model and the HG was the problem and that he cannot find anything else that could be wrong with it. He said it draining coolant is a clear sign of a blown HG. He offered me a $730 price tag to fix. Should I do it or get a 2nd opinion?

 
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well first thing is fisrt were is the coolant going look underneath is it leaking if it is find it and fix it could just be a bad heater core hose and i change my thermostat every year its only 4 bucks and check your oil dipstick is there coolant mixed with oil let me know what you find

 
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oh and also might be a leaking waterpump

 
Rep Power: 199

With the labor involved that is a good price IMO, what does it involve though? Low coolant doesn't always mean a HG though.