Run the grade your engine was designed for, change it on time, and a Miata engine is nearly unkillable. Here is what each generation wants.
| Gen | Engine | Viscosity | Approx capacity (w/ filter) | Interval |
|---|---|---|---|---|
| NA/NB | 1.6 / 1.8 | 10W-30 (5W-30 fine; 10W-40 in heat) | ~4 quarts | 3,000-5,000 mi |
| NC | 2.0 LF | 5W-20 | ~4.3 quarts | 5,000 mi |
| ND | 2.0 Skyactiv | 0W-20 | ~4 quarts | 5,000 mi |
Guidance: - NA/NB (1.6/1.8) - a good 10W-30 is the all-round choice; 5W-30 is fine in cold climates and 10W-40 is common for hot-climate or tracked cars. These engines are not fussy about brand, only about being changed. - NC (LF) - stick to 5W-20. The VVT phaser and oil control valve were designed around it; heavier oil slows the actuator and can set cam-timing codes. - ND (Skyactiv) - use 0W-20. The high-compression, high-revving Skyactiv depends on the thin, specified oil for its VVT and economy. - Track use - step up viscosity only if oil temps climb, and fit a good filter; a Miata on track heats its oil hard.
Why so cautious on interval: the wasted-spark and VVT hardware, the cam phasers, and the tiny oil passages all punish stretched, dirty oil far more than they punish honest miles. Frequent changes with the right grade are the cheapest reliability you will buy on this car.