1999 Honda Civic EX Overheating?

I'm going to try to explain this as efficiently as I can. My car has had a problem running hot since I got it a year and a half ago. The problem stops in the winter and comes back in the summer. This time it's much worse than usual. I have to add water to the radiator and the reservoir before every drive. There seems to be no water leaking anywhere at all, but I'm losing coolant like crazy. It makes me think there's an internal leak or that somehow the water is turning into steam within the system. I took the car to 3 different mechanics and was told 3 different things. One said there's a leak somewhere that he can't find, another said it's the water pump, and the last one said it's a blown head gasket. I don't know who to believe. I don't think it's the water pump, because there's no leak. I don't think it's a blown head gasket because there's no smoke coming from the exhaust, no milky oil, no oil in the radiator, no antifreeze on any spark plugs, and no loud engine. The same mechanic who told me it's a blown HG also told me that it wouldn't make sense to replace a HG without doing an engine swap which is another $2k that I don't have. The car has 196xxx miles on it, but the engine runs like a champ and these cars tend to last a very long time. Side note: I have replaced the thermostat, radiator cap, and cleared out air bubbles from the hoses. Anybody got any ideas of what exactly the problem might be?

Has anyone done a pressure test of the radiator & cooling system?

Hi so all this could be cured by simply replacing the radiator cap. It has a spring in it which keeps the pressure up so the temperature can rise above 100 degrees C.
over time the spring becomes weak this has the effect of losing the pressure in the system. So the effect is is it boils over loosing coolant down the overflow pipe.
as most modern engines run at 120 degrees C this is the most likely cause. So a new radiator cap which is usually on the expansion tank attached to the radiator.

Are you sure there are no leaks you can see? Have you tried putting a large sheet of cardboard under the car, both after you've driven and it gets hot, or overnight? It has to be going somewhere. I would tell you to replace the water pump, but that's an expensive repair, and you don't want to waste the money if that's not it.

Pressure test the system and the radiator cap to CHECK for leaks. Get a chemical analyzer tester to CHECK for a blown head gasket.

3 mechanics and none of them analyses the reservoir gases? When pressure builds up from a HG leak into the coolant system it flows out the reservoir top. While driving. Do the HG. No need for the engine swap. Get new mechanics.

The problem is you haven't found a competent mechanic yet. There's a simple test called a "block test" that uses a chemical that turns from blue to yellow in the presence of exhaust gases in the cooling system.

A leaking water pump can throw a lot of coolant you can't see leaking. When they wear out the shaft seal leaks fluid AND pressure. You need pressure to maintain a high boiling point.

1. You need a better tech.
2. Look under the front carpet for coolant. Your heater core may have corroded out.
3. Don't disregard the head gasket (or a corroded head allowing coolant into the oil galleries). There's no "standard" symptom for a blown gasket. The most obvious is milky brown gunge under the oil filler cap, and a high oil level. As it is floating on the coolant which is in the sump.
4. Check the radiator is not leaking with a pressure test. Check the condition of the inlet and outlet tubes, tighten the hose clamps and if they are hard, replace the hoses.
5. The pump will leave a small puddle of coolant under the car. They are designed with a small "witness' hole on the housing. If the pump seal fails, the housing fills with coolant and drips out of the witness hole. Put paper under the pump housing overnight
6. Get a new radiator cap. They are only a few $$ and it's easy to swap out

It is dying slowly.

You MUST use only genuine HONDA coolant and NOT prestone or other CHEAP coolants. CHnace are GOOD you ahve ONLY a BAD radiator cap and COOLING FAN SwiTCH here! Try runng it with the RAD cap fully OFF and see what happens! POWER WASH the ENGINE with GUNK ORANGE at a DIy car wash to remove excessive JUNK from the RADIATOR VANES, like INSECT bodies, LEAVES and GRASS that is dead! You clean on BOTH sides! LOOSING the RADIATOR HOLD DOWN to gain access to the RADIATOR! Use a CLEANING SYSTEM CLEANER and use ONLY that HONDA coolant in there forget ALl the JUNK at auto pzrts stores! ALL OF IT! Hond makes their very OWN COOLANT: do get i fromm the DEALERSHIP! If you were in MICHIGAN I woudl help you in person! Get NEW RAD cap from HONDA DO NOT trust ANYTHING after market only GENUINE HONDA parts and FLUIDS! Even the OIL must be HONDA spec oil and NOT from cheap il change places! EVER! >>M<ANY TIMES an engien with HG leaks can be cured SIMPLY BE REPALCING or RE torquing the HEAD BOLTS as they are ALL designed to S T R E T C H if the engien gets TOO HOT! Keeping the ENGIEN BAY CLEAN is SO very important since most cars run QUITE HOT under teh hood and are VULNERABLE to LEAVES< etc that get trapped in the radiator vanes, front and BACK! CLEAN is the nbame of the GAME ALWAYS! ALSO repalce the SPARK PLUGS with DENSO TWIN TI IRIDIUM LASER plugs! BAD plugs can ALSO make it run HOT! ALSO>>>>use AMSOIL POWER FOAM to cleant he THROTTLE BODY and the IDLE AIR CONTrOL vALVE to showroom so that it burns CLEANLY and gets the most fuel ileage and power! I don't know WHY car owners do NOT take cleaning the ENGINE BAY seriously as it is SO very important! I DOUBT you have a bad HG, but these things are the FIRST tio try.>>>also you can remove the SPARK PLUGS when engine is FULLY HOT and THEN trun the engien over! If the HG is leaking, then unwanted oil or coolant wil spurt out the plug holes!