Originally Posted by Cromax

If you wanted to know what oil to use, you could try these out:

Penrite HPR 5 5W-50?
Mobil 1 5W-30 (It's semi-synthetic and is rated the same as MRO)
Motul 5W-30 (I think it's the 8100 series one) or better.

I've personally only used Mazda Rotary Oil, Penrite and Mobil (in that order). I haven't used the Motul in my RX8 yet, but after playing with what I've used for fuel economy/performance etc. Mobil 1 comes out best by a long shot.

I find HPR5 to be too thick for everyday use fpr my application ... and the decreased oil use made me a bit nervous (as there was obviously less oil being pumped into the rotars) ... it goes a bit gritty like Mazda Rotary Oil does toward the 10000km change as well. which means it's oxidising before the oil change even with our 2+ litres of topups, which is bad!

Mobil 1 doesn't seem to oxidise as quickly as the others ... meaning it's the better oil out of those I've used. But that doesn't mean you shouldn't work out what's best for you!