Before You Start / Safety
- Start only with a fully cool engine.
- Ethylene glycol coolant is toxic: collect and dispose of all old fluid safely.
- Keep pets and children away from drains, pans, and open containers.
Warning: “Antifreeze is poisonous; avoid contact with your skin or eyes, and never consume.” https://www.wikihow.com/Flush-a-Radiator
Required Tools
- Catch pan(s) sized for at least 8 L total
- Funnel (spill-free style strongly recommended)
- Distilled water (for final mix and topping)
- Basic hand tools for drain plug / lower hose access
- Gloves and eye protection
Required Parts / Fluids
- Correct coolant for Mazda MX-5 NB (1998-2005)
- Distilled/deionized water (if using concentrate)
- Optional: new thermostat and gasket if due
- Optional: new radiator cap if old/weak
Model-specific notes (NB1 vs NB2)
- This procedure applies to NB1 (1998-2000) and NB2 (2001-2005).
- Community and independent references consistently place total NB coolant capacity around 6.0-6.2 qt (~6 L), while a simple radiator drain often removes around ~1 gallon, not all coolant in the block.
Manual-reference quote: “1999-2001 Mazda Miata Service Repair Manual” and “2005 Mazda Miata Service Repair Manual” are available in the Miata FSM archive. https://www.mellens.net/mazda/
Step-by-Step Procedure
1) Confirm coolant type and mixture plan before opening the system
If you are switching chemistry/type, plan a fuller flush sequence. If you are only refreshing like-for-like coolant, a simpler drain/refill may be enough.
High-risk quote: “the golden rule with coolant is not to mix two different types together.” https://bofiracing.com/blog/what-coolant-for-my-mx-5/
2) Drain old coolant from radiator (engine cold)
Open the radiator drain and collect everything. If the drain plug is damaged or seized, many owners remove the lower hose instead.
Community quote: “on teh bottom of the radiator is a little plastic screw … undo it and all the water drains out the radiator (take the rad cap off).” https://www.mx5nutz.com/threads/bleed-and-flush-my-coolant.6282/
3) If doing a full refresh, perform one or more water flush cycles
Refill with plain water, run until thermostat opens, cool down, then drain again. Repeat until drained fluid is significantly cleaner.
Community confirmation quote: “I pull the plug, drain as much out as I can, fill with clear water, run it and drain again… Then I drain it the last time, … put in my required amount of concentrate, and top it off with distilled water.” https://forum.miata.net/vb/showthread.php?t=515684
4) Refill with the right final mix (accounting for trapped water)
Because some water remains in the block/heater core after draining, using straight premix can under-concentrate final protection. Many NB owners add measured concentrate first, then top with distilled water.
Community quote: “Coolant capacity is 6.2 qt for a regular NB… If you flush with distilled, add 2 qt of coolant then top off with distilled” https://forum.miata.net/vb/showthread.php?t=515684
5) Bleed air from system and top reservoir
Run engine and continue topping slowly; squeeze upper/lower hoses to help purge trapped air. Re-check level after first drive and again when fully cold.
High-risk quote: “Continue to squeeze and release the hoses to help push any errant air bubbles out of the system.” https://techguys.ca/howto/coolant_flush.html
6) Post-service leak and temperature check
Verify stable operating temperature, heater output, and no leaks around drain point, hose joints, thermostat housing, and reservoir lines.
Torque Specs / Capacities
- Cooling system capacity (NB): commonly cited around 6 L / ~6.2 qt in independent/community references.
- A radiator-only drain typically yields much less than full system volume (often around ~1 gallon), so concentration math matters.
- Drain plug and hose clamp torque values vary with hardware and replacement parts; use year-specific FSM values where available.
Manual-reference quote: “The manual says it takes just over 6 quarts” (NB owner discussing manual value). https://forum.miata.net/vb/showthread.php?t=515684
Verification / Post-service checks
- Gauge remains stable at normal temperature in idle + road test.
- Cabin heat works consistently (basic indicator of flow/bleeding).
- Cold recheck next day: radiator full, overflow at proper mark.
- No sweet smell, drips, or wet hose/radiator seams.
Uncertainty / Open Questions
- Exact factory interval and concentration can vary by market/climate and coolant chemistry.
- Community advice differs on 50/50 vs leaner blends for temperate climates; this guide keeps conservative mainstream advice (target around 50/50 unless your manual/climate guidance says otherwise).
- Direct extraction of detailed NB cooling-system FSM tables was limited in this environment, so year/VIN-specific manual confirmation is still required for final spec authority.
Images
No reusable images were added in this run. Available forum images and how-to media did not provide clear reuse licensing suitable for this repository.
Image Credits
- No images used.
Sources
- Mellens (Mazda FSM archive) — Mazda Miata Factory Service Manuals. Retrieved 2026-02-26. https://www.mellens.net/mazda/
- BOFI Racing — What Coolant Do I Need For My MX-5? Retrieved 2026-02-26. https://bofiracing.com/blog/what-coolant-for-my-mx-5/
- TechGuys — How to: Flush your radiator / cooling system. Retrieved 2026-02-26. https://techguys.ca/howto/coolant_flush.html
- wikiHow — How to Flush a Radiator: A Simple Guide for Beginners. Retrieved 2026-02-26. https://www.wikihow.com/Flush-a-Radiator
- MX-5 Miata Forum — Is NB coolant change so simple? Retrieved 2026-02-26. https://forum.miata.net/vb/showthread.php?t=515684
- MX-5 Miata Forum — NB radiator coolant change. Retrieved 2026-02-26. https://forum.miata.net/vb/showthread.php?t=727302
- MX5Nutz Forum — Bleed And Flush My Coolant. Retrieved 2026-02-26. https://www.mx5nutz.com/threads/bleed-and-flush-my-coolant.6282/