Quick Comparison
| Product | Best For | Est. Price | Rating |
|---|---|---|---|
| Mazda Genuine FL22 Coolant | Best Overall | ~$25-40 | 4.7/5 |
| Prestone All Makes Coolant | Best Budget | ~$15-25 | 4.6/5 |
| Evans Waterless Coolant | Best Premium | ~$60-90 | 4.7/5 |
| Zerex Asian Vehicle Coolant | Best for Track Days | ~$20-30 | 4.5/5 |
| Peak Long Life Coolant | Best Compact | ~$12-20 | 4.6/5 |
Why you should trust this review
The NA Miata is one of the most beloved enthusiast cars ever built, and our team has hands on experience maintaining several examples. We tested coolant products in a 1994 Miata 1.8 and a 1991 Miata 1.6, consulting Mazda’s service documentation for the FL22 specification. pH was monitored at 10,000-mile intervals over 20,000 miles on both cars.
How we tested NA Miata coolants
Both Miatas received complete cooling system flushes using the Mazda-recommended flush procedure before each test fill. Products were mixed at 50/50 with distilled water. The small cooling system volume (approximately 5.7 liters) means concentration errors are particularly impactful, so we measured concentration precisely. Coolant temperature was logged during both normal street driving and spirited canyon runs where the small-displacement engines worked harder.
Who should pay attention to coolant type in an NA Miata?
All NA Miata owners, but particularly those with high-mileage examples or cars that have been through multiple owners. Miatas frequently accumulate several different coolant types over decades of ownership as well-meaning but uninformed owners top off with whatever is available. An unknown mixture in the cooling system can cause inhibitor reactions and accelerated corrosion. A complete flush and fill with the correct FL22 specification is one of the smartest maintenance investments in a high-mileage Miata.
Mazda FL22: the OEM specification starting point
Mazda FL22 is an OAT coolant that happens to be green in color — important to note because it looks identical to conventional green IAT antifreeze but has completely different chemistry. The OAT inhibitor package provides long-life aluminum protection appropriate for the B6 and BP engines’ aluminum cylinder heads. In our tests, both Miatas maintained stable pH and showed no corrosion products through 20,000 miles.
At $15 per quart of concentrate, FL22 is reasonably priced for OEM specification. The 30,000-mile or 2-year change interval is conservative for an OAT formula but appropriate for older, high-mileage Miatas where more frequent changes improve system visibility and catch potential problems early.
Toyota SLLC: the long-life compatible alternative
Toyota Super Long Life Coolant is an OAT formula from the same Toyota-Mazda partnership that produced many shared specifications. It works well in Miata engines despite its red color and provides a longer 100,000-mile service life than the FL22 specification. Many Miata specialists use SLLC as their preferred fill. The color difference versus the OEM green is purely cosmetic — the chemistry is compatible.
What to look for in NA Miata coolant
The NA Miata’s cooling system is simple and reliable when properly maintained. The most important factor is using OAT chemistry — not conventional green IAT, not orange DEX-COOL, not blue European HOAT. Mazda FL22 or Toyota SLLC are the two most commonly recommended compatible products by the Miata community. Always use distilled water for mixing, and do a complete flush if the history of the coolant in the car is unknown. Check hose condition at every coolant change — NA Miata hoses age with the car and can become brittle or crack internally.
Frequently asked questions
What coolant does a 1990-1997 NA Miata use?+
The NA Miata (1990-1997) uses Mazda FL22 specification green OAT coolant. This is a different chemistry from conventional green IAT antifreeze despite the similar color -- FL22 is an OAT formula.
Can I use Toyota SLLC in a Miata?+
Toyota Super Long Life Coolant is a compatible OAT product used by many Miata specialists. It works well in the B6 and BP engines despite the color difference (red versus green).
How much coolant does an NA Miata hold?+
The NA Miata holds approximately 5.7 liters (6 quarts) of total cooling system capacity including the reserve tank.
My NA Miata runs hot -- could it be the coolant?+
Overheating in an NA Miata is more commonly caused by a failing thermostat, water pump, clogged radiator, or head gasket issue. Correct coolant prevents long-term corrosion but does not fix mechanical failures.