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Honda Civic 2000-2005 Problems
They've replaced the thermostat, the hoses connecting the radiator and the radiator cap. No difference. They've tested the oil for any traces of coolant. No traces. They've let the engine cool for about 5 hours and pressure tested it. Nothing apparent.
The leak loses antifreeze over months but seems to be speeding up. I've noticed the heater stops working a few days before the engine begins to overheat (so I put in coolant). There aren't any puddles under the car.
Leak sealant seems to have helped the problem before, but I am not sure it is now.
The overheating also seems to happen in the pauses after long trips. I took a 70 mile trip today, and then it began overheating when I got off the expressway. I had checked the antifreeze levels before I left but haven't checked after because it is too dark.
There was something new today. I also smelled a bit of a chemical smell towards the end of the trip but not during it. Of course, I also went through an industrial area.
There is also no apparent wet spot inside the car and on the floor under the dash, where a leaking heater core would create that mess.