This is my first post here, so if it is in the wrong place, let me know and I'll repost where it should go.

So here's the basic story.

05 Honda Civic EX.

About a month ago I'm sitting at a redlight and happen to glance down and notice my temp gauge working its way to H rather quickly. I plan to pull over but as soon as I start driving again it goes immediately back down. I'm a mile from home so I get home and check the engine. Oil isn't cloudy, no smoke, no check engine light, both rad hoses are hot...I begin to think I'm hallucinating.

The next day, it does it again. So I get some coolant, check the levels and they were low, so I top it off. It seems to run fine for a day or two.

Few days later, doing it again. So I think maybe my thermostat failed. Go pick up a new thermostat and gasket and replace it. I drive it around for a while and also let it sit and idle for about 15 mins. The gauge never get above about 1/3 of the way up (pretty normal for my car).

Few days later.....doing it again. So, I take it to the crappy pep boys. They do a coolant pressure test, say everything is fine. They then replace a temp sensor (think it was the one on the water bypass?? not sure). It runs fine for a day.

Day later, does it again. So I angrily take it back to pep boys and they bleed the lines and leave it running in the parking lot for about 2 hours and the temp never spikes.

Later that day, my temp gauge is still spiking while I'm sitting at red lights.

Now, it seems like the gauge is doing it just to **** me off. I check it when the gauge is sitting at H and the hoses are hot and there is no smoke and I have no idea what to do next.

Apologies that this is long, but I have no clue what else I should be testing. I'm not great with cars...I can change my oil and brakes and crap, but troubleshooting is not my forte. I think I've just been guessing.

If anyone has any advice, PLEASE offer it.

 

Make sure the cooling system is properly bled, if not air can gather at the thermostat housing and create a false overheat.

How much antifreeze are you adding?

Look down by the fill port on the radiator, there is a small tube that comes backward off of it that runs to the surge tank/bottle. Is the surge tank overfilled or the hose disconnected? Can you shine a light down the fill cap opening and inspect the core for blockages or corrosion?

Hard to be sure, but if you do not leak, the thermostat is new, temp sender is new, and if the radiator fan works, you most likely have a head gasket expansion leak into the engine. Very common on the 1.7L. Lets hope I'm wrong, but in this case its sounds pretty definitive to me.