does anybody know what happens or what needs to be done when your car is running on full synthetic oil and then you put in conventional oil without flushing your engine?

 

Nothing really... you wont kill anything... just change back on yor next change...

 

I run 0w40 Mobil 1 in winter and 10w30 Valvoline for the other 3 - 90 day cycles and pretty much have for the last 7 years since the engine turned 200k now at 318k and 18 years of service, but obviously the old Q45 V8 was more forgiving than modern lighter duty V6.

Success will depend on your understanding local temperatures and oil viscosity relationships.

 

nothing will happen. i don't know of too many synthetics that are not compatible with regular oil

 

Most anyone that has anything to do with the automotive industry is of the
opinion that once you use synthetic oil you can't go back to conventional...
and why would you? Synthetic oil is sooo much better for your VQ engines
and runs far cleaner without leaving any build up of gunk, switching back
bridges on stupidity.... Of course if you don't care how your G35
runs use whatever you want.

 

I think the OP was saying he did it by accident and just wants to know how to get back to synthetic without damaging anything.

Just refill with synthetic on your next change - no harm done.

 

^+1

 

Absolutely nothing will happen. It's fine. You probably won't even notice the difference if the viscosities are the same/similar

 

Oh please. Step away from the keyboard and go outside. The sun is shining and you need a break.