Hello,
One of the common causes for coolant mixing with oil is when the head gasket fails.
The head gasket seals the cylinder head to the engine block and overtime it can fail and that will let coolant enter and mix with oil. This will typically produce white smoke out of the tailpipe.
Here is a helpful guide:
https://www.2carpros.com/articles/coolantantifreeze-in-the-engine-oil
You did not include the year of the Malibu, so I have attached the head gasket replacement procedure for a 2000 model year with the 3.1L engine.
Let me know if you have any questions.
Thank you.
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Thursday, December 8th, 2022 AT 10:57 PM