My 2007 Honda Civic is losing coolant?

My civic has 108,000 on it. About a month ago my car started to overheat, discovered it was low on coolant so i filled up the reservoir and radiator and did not have any further problems. I typically make a 4 hour drive every other weekend one way and my last trip as soon as i got into town my temperature gauge was indicating that my car was running hot, i checked my coolant the next morning once the car cooled down and the reservoir was practically empty and my radiator was not i could see the coolant. I then filled up the reservoir some more and closed my hood but a few days later the reservoir was low AGAIN, (i did not fill it up too much) I'm curious to know what could cause this? My oil does not have any white in it, it is not leaking (other than some water from running the AC) and no smoke is coming out of the muffler. It has not gotten warm again since that night i returned from my 4 hour drive. Am i over thinking this and being paranoid? Should i try replacing my radiator cap?

After an older Honda engine overheats, the head gasket often fails. You should certainly be cautious, do get a compression test to check your cylinders heath.

You've sound like my youngest daughter (she's 20): She does not know how (or want) to check the fluid levels in the car so that was the phrase she use: I've discovered my oil light came on or my car has no heat today etc.

Overheating on your Civic could be anything, a simple cooling system pressure test will reveal that where the coolant went: External leaks cab be locate and repair like cooling hoses, radiator, radiator cap, water pump etc. In other hand: Internal leakage will involve more difficult to locate that requires the "Know-how-to" and different testings; most likely it could be a head gasket, crack head or crack engine block.

Does the tail pipe has extensive, thickened white smoke? I'm not talking about a little "Water vapor" white smoke in a cold start morning and dissipate quickly into thin air after the engine has warmed up: That's normal. If the answer is yes: Then most likely the head gasket has failed.

Whatever has failed, do not drive the car until the cause is found and proper repair take place. Things you can do now is check the engine oil level and condition (Like the color has changed to a "Milky color) and adding water, do a visually inspection in the engine bay and see if the is any leak. If not then see if the fans come on when you turn the AC on or running when the engine is up to operating temp (The temperature gauge indication is about haft way) etc.

Beyond what you can do, find someone who know how to help or get the car to a repair shop for further testing to find out the cause(s).

Radiator cap, coolant hoses, engine thermostat, cooling fans, radiator, water pump, head gasket etc. Are among the most common things to check when an overheat engine is "Discover" (Just kidding!)

Edit: If you or someone is helping you want to do the testing/repairing and need help to do so; then send a message and I'll give the instruction how to do so. HTH

The radiator cap will fail over time. If it does not retain the pressure that it was designed to, the coolant will boil at a lower temperature, every pound of pressure raises the boiling point 3 degrees. If water boils at 212 under no pressure, it will boil at 242 under 10 psi. Test the carp. At the same time, water pumps do not last for ever but you did not mention any visible leaks.

I would do 3 things if i were you! First i would change the thermostat, then flush out the cooling system and replace the radiator hose! If the reservoir keeps going low all the time then you either have a leak or it, s using it! Since you said no antifreeze is in the oil and no white smoke coming out the tailpipe then it, s safe to say it, s not the head gasket! Did you check the floor on the passenger side? Maybe the heater core is leaking!

Thank you everyone, i'm going to replace the radiator cap today and if the coolant is low again by monday i'm taking it to the shop. I will keep you all posted