Possible Head gasket Failure 2009 Astra CD Auto Z18XER.

[HoldenAstra]

Check oil cooler, also a friend of mine had rocker cover gasket failure as well on this car.

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[Astro64]

Ok I will have to have a look for the oil cooler as I`m still getting acquainted with the car.
It seems the oil in the expansion bottle is engine oil.
The thing that threw me off diagnosing a head gasket was the fact that the cap and the bottle didnt have that characteristic engine oil smell.
Also no milky oil anywhere. Im wondering If that is because the engine oil is full synthetic.
Also the Oring on the expansion bottle cap has lost its elasticity and has deformed. It definitely wont seal now and will certainly overheat. A mechanic I know said he wants to see the oily cap and went on to say he hasnt heard of Astra`s that have head gasket issues.

[Astro64]

Check oil cooler, also a friend of mine had rocker cover gasket failure as well on this car.

Thank you HoldenAstra It turns out my oil cooler may be cracked somewhere and letting engine oil into the coolant.
The spare part is @$600 so not happy about that especially if this is a common problem. Im about to call Holden to see If this part has been superseded.
I have also tracked down a replacement oil cooler in China which delivered comes in just under $200. I will have to wait @ 4 weeks for that to arrive though.