Showing specs for all NA & NB Miatas

Engine coolant type and antifreeze mixture (NA6)

Ethylene glycol-based coolant mixed with soft (demineralized) water; By volume: 35% coolant / 65% water for protection above −16°C (3°F); 45% / 55% above −26°C (−15°F); 55% / 45% above −40°C (−40°F). Do not use alcohol- or methanol-based coolant.
Factory manualTaken from a Mazda factory workshop manual, with page citation.
Procedure

Never remove the radiator cap with the engine hot. Ratios are coolant/water volume percentages, not a universal fixed mixture.

Applies to
  • NA 1990–1993 (B6) — Other years in this family inferred from 1990 factory evidence with owner approval; actual-year verification is separate.
  • Verified in: 1990 Mazda MX-5 Miata Workshop Manual
Sources
  • 1990 Mazda MX-5 Miata Workshop ManualTier 1
    Part no. 1193-10-89C
    Page E–5 (PDF p. 135)
    Ethylene glycol-based coolant mixed with soft (demineralized) water; By volume: 35% coolant / 65% water for protection above −16°C (3°F); 45% / 55% above −26°C (−15°F); 55% / 45% above −40°C (−40°F). Do not use alcohol- or methanol-based coolant.
    Printed: “Antifreeze solution mixture percentage Coolant protection Volume percentage Water Coolant Gravity at 20°C (68°F) Above −16°C (3°F) 65 35 1.054 Above −26°C (−15°F) 55 45 1.066 Above −40°C (−40°F) 45 55 1.078 Fill with the proper amount and mixture of ethylene glycol-based coolant by referring to the table above.”

Also in Additional factory manual gap audit