i have replaced the thermostat, radiator cap, and water level sensor. hoses are in good shape and i am pretty sure the radiator is doing its job. however after posting about this before, trying to get the air out of the radiator is turning out to be a big hassle. i have run the car at idle for 30 minutes to bleed it, and i have run the car down the street and stopped, released the cap and let the air out, and repeated several times. the car was fine for about a week and then after sitting for a day or two it started buzzing at me with the add coolant light again. it all started after the first time i let the car sit for more than a day. could letting the car rest have something to do with it? at this point i am expecting the worst, but any input as to how more air can be entering the cooling system would be appreciated.

 

isnt it weird that the water seems to "disapear"?? mine does the same thing, but only to a point. I had to disconnect the sensor because it just doesnt seem to like to hold all that water but never runs dry. It has to go some where. You will know when you have a problem

<----------------- see that picture? that is a broken center steel cooling jacket and you will suck ALL the water at that point.

 

i have the same exact problem. i also disconnected the level sensor, i had to ground it because everyday it would go off and i had to drive with that beep.
ive had the problem for about 5 months, sorry im poor and dont have time/money to get professional help, and the water level problem is getting worse. i figure its a gasket or seal inside the motor that has failed and coolant is enter the motor causing hard starts and coolant loss oh yes and air in the coolant.


does the coolant smell like gas?
hard starts?

 

It takes a few times to open /bleed to get the bubbles out.
The procedures are:
1.fill to top and cap
2.let it get to operating temp and let it cool
3. do same procedure again.
For the time being, you could ground the sensor until it's bled.
If you keep having to fill, you have a leak obviously.
Look for traces of white residue around the turbo coolant line, water pump weep hole (if the pump is failing, water will seep out). You could have it pressure tested at a shop to find leaks you can't see.
Try this:

Open the radiator cap and look inside while the engine is running. Is coolant being pushed out or are there bubbles in there? If yes, you could have a cracked O-ring which will get worse over time.