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Q: Hi i have 2000 s70 volvo head gaskets are good but i have this milky stuff in my coolant resevoir any ideas what is causing this

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I have milky looking stuff in my coolant resevoir and my radiator light is on

My car has 400000 miles.
My car has an automatic transmission.

Hi there. Assuming you don’t have a coolant leak inside the motor, it is quite possible that the milky residue is mold due to regular water being used to mix with the coolant as opposed to distilled water. Tap water contains minerals and other particles that when heated can create different types of mold to develop on the radiator cap and inside coolant lines. This is why it’s always recommended to use distilled water when filling coolant as it will reduce the potential of mold growth. If mold has developed inside your motor, I would strongly recommend having the coolant system flushed at the minimum and replacing the coolant lines, and coolant reservoir; as it will eventually spread to the heater core and create an overheating problem.

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