[svx_commuter]

Head gasket. Sorry but that is a classical discription of a Subaru head gasket leak. I recently pulled a 2.2L engine that passed all the head gasket tests, pressure and CO gas in the coolant. The leak was too small to show up. The engine ran great on loacl driving but on the highway it sucked coolant and over heated. Not the same as your case but blowing coolant out the tank lid is common with a HG leak. The over heating does not always show up on the gauge. Depends on how close the leak is to the sensor. I know of another SVX that showed increased gauge temperatures at idle in traffic. The gauge would go up and down. It was a HG too.