Mazda recommends not to use sythetic because they have not done "testing" with synthetic oils. As long as you get an oil the burns fairly cleanly, you should be fine. Mazda also says to use 5W20, do you?

 

I get my oil changed at the dealer, and use whatever oil they put in. For the first couple of years that was 5w20. For the last few changes they've used 5w30. Based on the Australian oil chart and my own prejudices, my preference is 5w30.

I did describe my exchange with Valvoline as "amusing." I think the best thing about the synthetic debate is that it keeps traffic on this site high, so the owners make enough money to keep it running.

Ken