How do I test the coolant for combustion gases? I have drained the coolant and looking at it it looks fine. I looked for traces of oil and there are none.

Thank you for you help.

I recently purchased an XC90 T6 which has been to the volvo dealer often (have receipts from previous owner). There is random white smoke coming out the tail pipe. It has happened twice. the smoke then disappears with no apparent consequences. Can anyone help with this?

Thanks