Actually its a Leone (Australian name)

 

Here is the deal.

 

A few months back my cooling fluid has started to collect in the expansion bottle, overflowing it after some driving, even with the cap on.

 

After checking for coolant leaks, and finding none, I am scratching my head. It seems that AIR is somehow getting into the cooling system, thus displacing the fluid into the expansion bottle.

 

The system is under pressure OK, as when I open it hot, fluid shoots out, and when I open it cold air gets sucked in/out.

 

Fluid is definitely running out through the expansion bottle (I think), as I have to keep topping it up.

 

Here is the clincher: this seems to happen mostly after prolonged driving at over 80 km/h (I think).

 

The water burbles in the expansion tank when I turn the engine off. Dont know whether this is air or coolant.

 

Also, I dont think its the head gasket as there is no coolant in the oil and no oil in the coolant.

 

Sorry about the long post, but I am getting desparate.

 

Help?

You don't mention whether your temp guage is indicating it's overheating. I would check the thermostat and make sure you're running at a safe operating temp. You might also have a blocked radiator, which isn't uncommon for a car this old.

 

As far as the head gasket goes, oil and water mixing often isn't present with a headgasket leak. What leaks is combustion gases, and they leak into the cooling jacket, which is why you get bubbles. To be sure, you can have your local shop check for combustion gases in the coolant, or you can buy a tester to do it yourself - they cost between $20 and $30 in the US. It consists of a clear tube with a neoprene cone at the bottom. You partially fill the tube with a test liquid and then place the cone on the radiator fill tube with the engine running. If combustion gases are present, the fluid will change colors.

it only overheats when it runs out of coolant (which gets pushed out of the overflow bottle)

I would check for combustion gases.