SPM-QMX - SuperMiata coolant reroute kits

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Part #: SPM-QMX
Your Price: $249.00

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Year Model SubModel Cylinders Liter Aspiration Eng Desg. Fuel Notes

Product Description


The B series engine in the Miata was designed for a FWD car. As with all inline 4 cylinder engines, coolant entered into one end of the head and exited the other end. This simple path is the most efficient way to extract heat from the head.

When Mazda chose the 1.6L B6 (then, later, the 1.8L BP) for use in the Miata, they repurposed the motor used in the 1985-1989 FWD BF chassis 323 which had the water pump near the right fender and rotated it counterclockwise 90° with the water pump facing the radiator. This placed the coolant outlet very close to the firewall, making it impractical to retain the thermostat at the “rear” of the head (opposite end from the pump).

In an unfortunate design compromise, they moved the thermostat and coolant exit to the pump side of the head, on the same end as the inlet. This poor flow path is the primary cause of the overheating which is so common in highly modified NA/NB Miatas. Even completely stock Miatas, when pushed, will run a bit hot, causing the stock ECU to retard ignition timing, reducing both power and fuel economy.

The SuperMiata coolant reroute kit has a carefully engineered low-profile thermostat housing for the rear of the head to restore the original uncompromised front-to-back coolant path. Just this one modification will significantly reduce coolant temperatures.
To learn more about the NA/NB Miata cooling system and how to improve efficiency, view this forum thread.

Preview the installation manual.


• internally machined to maximize coolant velocity which is key to improving cooling efficiency
• compatible with 1994-2005 EGR cross-pipe
• stock coolant temperature sensor location is retained so wiring harness does not need to be extended
• spare 1/8” NPT ports for aftermarket coolant temperature or pressure sensors
• hardware is Stainless Steel for maximum kit lifespan
• internal high-flow Stant Superstat thermostat for maximum coolant flow
• no remote thermostat housing for easy fitment and improved reliability
• simple sealed adapter housing has no leak-prone gaskets or threaded fittings
• convenient bleed port allows coolant system burping with car level (if you have COP ignition and can access behind head)
• kit installation should take an average mechanic using common hand tools just a few hours


(1) rear housing
(1) cover, thermostat
(1) block off plate, head coolant port
(1) block off plate, coolant neck
(1) internal snap ring, 1-11/16” D
(1) Silicone hose, 1.25” D x 44” L
(3) bolts M6 D x 1.0 TP x 25mm L
(3) plugs, 1/8” NPT
(1) bleed screw
(1) hose clamp, 5/8” D
(2) hose clamp, 1.25” D
(1) hose barb, 3/8” NPT
(1) drain plug, M16 D x 1.5 TP
(1) thermostat, Stant
(1) sealant, Permatex


• internal snap ring pliers
• metric Allen keys