I have the same question. Either that is at fault or I need a new sensor.

 

yeah but the gas costs you $6/gallon in europe

 

Pressure test sounds good for anyone with this kinda problem. I was pissin coolant all over the place after I reinstalled my engine and I couldn't figure out from where because it would only do it if it was really hot. Did a ghetto pressure test and sure enough coolant started literally spraying out from one of the fittings. Tightened it to hell and it was fixed. Burped system 6 or so times and has been fine. Only other time I was consistently losing coolant was right before my 1st engine went due to age.
My $.02 on the AST level deal.....
height above or below engine doesn't matter here. The highest point in the system is really the filler neck either way (in a sense) the filler neck will push coolant and air that accumulate in it to the ast no matter the height. The return of the coolant from the ast to the engine upon cool down comes from a line at the bottom of the ast. Bubble in the ast will rise to the cap and not go through the eng-ast hose...... unless you have it turned upside down. Am I right in thinking this...

 

IT WAS LEAKING INTO THE CAR!!!

THE passenger side floor had a green pool beneath the carpet......just lift your carpet on the passenger side and if there is a pool of coolant its you heater core.