Just had the 8 back from its major service only at 26000 miles.
I aksed Mazda what oil they used to service the car so I could match it to top her up when needed with the same oil....

He said they used a "semi synthetic, 5w 30 oil" And I had just purchased a big new tub of Motul 8100 5w-30 (fully synthetic) as reccomended by opieoils.
I said can u mix that with a fully synthetic so i can top it up, he seemed to have no clue what so ever, and just said, "umm not sure, err no probably not"
There were no mechanics at the time to talk too...

Can anyone here give me an answer please?

Thanks

James

Go ahead and mix it. You can only get about 60% of the RX-8's oil out during a change so if you change brands or whatever you're forced to mix it. I haven't heard of any problems from it.

Some years back, there was the potential issue of "additive clash" with different brands, but from what I read that is no longer a serious problem. Bottom line, as LionZoo says -- you will mix it one way or another unless you want to go to the trouble of forcing all the old oil out of the system.