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Why is the coolant in my 2007 Holden Astra a milky colour?

Asked by Michael

Why is the coolant in my 2007 Holden Astra a milky colour? The engine oil is clean as a whistle.

Answered by CarsGuide

10 Feb 2021 David Morley

The first response of most mechanics on this would be that you have a head gasket leak in the engine. Coolant in the oil and/or oil in the coolant are classic symptoms of this. It happens because the faulty head gasket allows the two fluids to mix but, depending on exactly where the gasket fails, you don’t necessary get both symptoms. A workshop can pressure test the engine’s cooling system and perform what’s called a TK test to show up any contaminants in the coolant that have found their way there via a blown head gasket.

But before you go tearing into the engine, check the service records to find out how old the coolant is. Coolant will discolour over time and kilometres and what you’re seeing as a `milky colour’ might simply be old coolant that has gone cloudy and needs changing.

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