Ok so I have a 2008 350z has I am trying to figure out the causes of coolant mixing with oil inside the motor other than head gasket didn’t drive it for 2 days I put an exhaust on afterwards turned it on let it warm up for a bit & revved it to hear how it sounded a small puff of white smoke came out the back then cel came on indicating multiple misfire & p0011 code I turned it off immediately,checked the oil & saw the Milkey oil. Drained it all out & never turned it back on since. In the process of taking the heads apart to see if I can spot some blown gasket so far I’ve notice the gallery gaskets need replacing but that’s it don’t know if it could be a cause too?oil pressure never dropped. I've heard that failure on internal water pumps could be a cause.thermostat was old but good. Water was used as coolant by the previous owner don’t know if that could possibly affect it ? Didn’t notice until the leak & drained everything