Coolant overflow signum 2.0t 2003

[Ping]

I have a signum 2.0t 2003 recently oil cooler failed and discharged oil into cooling system,had a very good 2nd hand oil cooler installed & system flushed 3 times.

all works fine until temp gauge gets to 90c water starts to bubble and blows out of overflow oil cap clean no cream on it

any help appreciated 

[Vauxhall Owners Club]

There could be a slight possibility that the head gasket could have failed as if there was high pressure in the coolant, that could have led to failure of the oil cooler...just a possibility but worth running a coolant block test (chemical changes colour if combustion gases present).

Alternatively, a more simple and cheap option may be that the coolant pressure cap has failed and not maintaining pressure in the system.