Haven't got my own car with me or any diagrams etc, and the thermostat is one thing I've never even needed to look for, so can't say if this is correct.
I'm assuming your GF's 8v is the AGG like mine, and not the earlier 2E engine. Think they changed over around 96/97?
Air bleeds for the coolant are little screws (like bike tyre caps) on a 1" or so dia hose coming out of the bulkhead at the top near the middle. As you stand in front of the engine, just to the right of the inlet manifold/throttle assembly. The Idea is: get the car up to temp so the thermostat should be open, run the heater on hot with the engine running on idle, and open the bleed screws. Have a bucket/jug of ready mixed antifreeze handy (should be 50/50 I think) and keep topping up the expansion bottle until you have a nice steady stream of coolant coming out of the bleeds. Then whack the caps back on them quick as you can without letting teh level get too far down...
Other things that could be a
problem are; internally collapsed hoses, internally collapsed or blocked radiator, generally high levels of gunk in system.
You'd only get the mayonnaise in teh oil if the head gasket had gone again... Think yourself lucky!
You can get a good idea of whether pipes are likely to be causing problems by giving them a good squeeze when they're cold. They should be quite stiff. If they're very soft you may have found your
problem or possibly next weeks'
problem...
I've heard a few horror stories about mk 2
ibiza radiators. Mine was replaced about 3 years ago...
