Rep Power: 0

i have a 2005 honda civic..it holds pressure and shows no leaks with a pressure test and there is no water in my oil and no oil residue in my overflow bottle....but it slowly loses fluid and back pressures it into and spits it out of the overflow bottle at high rpm and long journeys....im perplexed and looking for help....what would cause this if its not the head gasket( which it appears not to be and it was just changed about 25,000 miles ago as well)...would a faulty thermostat cause this? and it does not overheat unless i let the coolant get too low from losing it out of the bottle...also it has a new radiator cap as well

 
Rep Power: 224

It's the head gasket. Read up. Combustion gases leak past the head gasket into the water jacket. That forces coolant out into the reservoir, overflowing it after enough time.

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