So my civic has been running hot this week. Had plenty of antifreeze. Oil.changes and tuneup are up to date. Started running hot monday so I went ahead and changed the radiator cap and replaced the thermostat. Still running hot at this point and im losing all my fluid from the coolant reservoir. I run my heat as a guide to when I lose all fluid. Once the heat turns cold I pullover and refill it up. Oil isnt milky and no white smoke. Could it still be a bad head gasket? Possible water pump? Plan to flush the radiator tomorrow. All opinions and advice are welcome
Unfortunately with this age Civic you may be looking at a head gasket. See if you can get the radiator pressure tested, that will show leaks in the system (including the head gasket) Keep an eye on the fluid and do not let it overheat to prevent any more damage
To see if the head gasket is leaking, when the engine is cold remove the radiator cap.
Start the engine and while the engine is idling watch the coolant in the radiator. If bubbles begin to appear in the coolant that confirms the head gasket is leaking.
I suspect a bad head gasket. I had similar problems with my '03 Civic for about a year at the 150K mile mark. Tryed some of the stuff you’ve done, and eventually had the head gasket replaced and all problems were resolved.
Your post is a little confusing. At first you say you observed plenty of coolant, then later you say – apparently after you replaced the cap and the thermostat – the coolant is low. If so, it might be a coincidence and the coolant would have started getting low anyway due to whatever the problem is. But it’s also possible the cap replacement or thermostat replacement is causing the low coolant problem. Is there any sign of coolant or steam leaks from those areas? When you replaced the thermostat you probably had to partially drain the coolant. Did you air-bleed the coolant system after you did this?