If you
run the stock OMP and feed crank case oil as the lubricant I would avoid both
racing oils and multi grade oils. The long chain polymers of the multi
grade tend to gum and don't burn well. The racing oils are also very stable at
high temps and don't burn well, plus less detergent action would require
more frequent oil changes and much greater expense.
I use the OMP and pan oil. I would
have thought that an oil “specifically
engineered to meet the unique requirements of a rotary” would take that into account and be clean burning. But maybe
that’s just marketing. I understand the Idemitsu is recommended for
the RX8.
I talked to a guy a Mazdatrix who sells
the Idemitsu, and one of his comments was that they’ve had good luck with
the Castrol. Maybe I’ll stick with it and change more often; I can
change it about 5 times for the cost of one change with the Idemitsu.
Besides; I always have some around because I’ve used it all my other
vehicles for years with exceptionally good results.
Al