What type of oil should I use in a Mazda RX-7 FD?

The 1993-1995 factory service manual specifies conventional (mineral) oil in 5W-30 or 10W-30 weights for a stock FD RX-7 ¹. Beyond that baseline, the right choice comes down to managing heat, protecting the engine's internals, and accounting for the rotary's unique oil consumption — depending on your climate and modifications, there are a few proven approaches to consider:

Viscosity For normal street driving, 10W-30 is ideal for fall, winter, and spring. A thicker 20W-50 is highly recommended for the summer or if you live in a hotter climate ².

Conventional vs. Synthetic Conventional oils, like Castrol GTX, are a proven and popular choice ⁶. They are cost-effective, which is important because rotary engines require frequent oil changes due to fuel dilution.

If you prefer synthetic, Idemitsu is highly recommended because it is specifically formulated to burn safely in a rotary engine without leaving harmful residue on the spark plugs and apex seals ¹. Avoid standard off-the-shelf synthetics if your Oil Metering Pump (OMP) is still injecting engine oil, as standard synthetics do not burn cleanly.

Additives (ZDDP) Oils with high Zinc (ZDDP) content, such as Valvoline VR1 Racing Oil, offer excellent bearing protection. However, you must avoid high-ZDDP oils if you still have a catalytic converter installed, as the zinc will quickly damage it ⁴.

Change Intervals and Filters Because of fuel dilution and the fact that a significant amount of old oil remains in the rotors and oil coolers during a drain, you should change your oil every 1,500 to 3,000 miles ⁴.

For the filter, stick to an OEM Mazda filter. An excellent upgrade is using the 2009-2011 RX-8 Series 2 filter (Mazda Part # N3R1-14-302). It has a higher bypass pressure rating (20.3–26.1 PSI compared to the standard 11–17 PSI), which provides much better filtration at higher RPMs ⁴.