I've been having a problem with my WRX, it's loosing coolant but I don't see spills, my radiator doesn't make air bubble over time it just spills it when the thermostat is open, my overflow tank doesn't bubble either and there's another little tank in the side of the engine and still doesn't bubble unless I rev the engine which is water being agitated. I believe it doesn't spit water when I turn the engine on. There's no water getting in the oil nor oil getting in the coolant and no water vapors out the tail pipe when driving hard. Any suggestions?
The coolant must be going somewhere. If you don't see any external leaks, the leak must be an internal leak. Head gasket would be the usual suspect here. Perhaps the leak is so small that you just don't see the water vapors? I.e. the coolant can still be going to the combustion chamber in small amounts that are invisible in the exhaust.
I would recommend you to have your coolant system pressure tested. It will reveal if the head gasket is leaking coolant into the cylinders. The diagnosis shouldn't be too expensive, and will lead to useful information to decide what to do with the car.