How bad is synthetic oil for the rx-8 and would it be ok to switch to regular oil with the next oil change.

 

Synthetic is fine. Just don't run the Mazda recommended 5w-20 as it is too thin. Run a minimum of 10W-40. There is a huge thread on this as well. Put on your reading glasses.

 

Read the "Similar Threads" down below for more information. Recommended oil is 5w-20 and you could use up to 40 weight as stated above. As for your question, synthetic blend is okay to use, but when you ask other people, they will not recommend it. Read more to find out, good luck.