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During design of the original MX-5 Miata, an already existing B-series engine was used to power the car. They rotated the engine position by 90 degrees and moved the coolant outlet from back to the front of the engine, resulting in change of coolant flow. Because the coolant inlet and outlet are now both at the front, much less coolant is getting to the rear of the engine, thus less heat is taken away from cylinders at the back. This applies to all models from 1989 to 2005 (first two car generations).

This modification also dropped the efficiency of the whole cooling system. Mazda compensated for it by installing a larger radiator, but this design still struggles under high loads and cylinder 4 runs considerably hotter. This difference in temperatures is measurable and was proven years ago.

Mazda knows about this issue and tried to fix it by changing the head gasket in NBFL (MK2.5) models. This new gasket restricts flow to cylinders 1 and 2, so more coolant is forced to the back. That is why 2001+ cars suffer from the issues mentioned a bit less, but in our opinion restricting the total coolant flow even more is not a proper solution.

Coolant reroute is moving the front coolant outlet back to the rear and restoring the original engine design. You can learn more about the advantages in the next section.

  • Engine without reroute

    Mazda MX-5 Miata engine without coolant reroute
  • Unequal cooling across the engine block, resulting in different combustion conditions from piston to piston. This induces uneven wear and tear on all parts. Also the overall heat transferred from your engine to the coolant is poor due to "front in - front out" design. Because of this it's wise to keep an eye on your oil temperature when driving hard, like on the track or with forced induction.
  • Piston rings and other parts wear is increased in rear cylinders due to stress from higher temperature. Bad piston ring seal leads to increased oil consumption, worse emissions and decrease in power. This is measurable as compression test values decrease from front to back cylinders. Compression loss does not happen quickly on street driven cars, but the engine resealing is quite expensive.
  • Carbon deposits build up much quicker on the valves with high cylinder temperatures. This happens when fuel and oil comes to contact with very hot valve surface. The deposits create turbulence causing decrease in performance and problems like stumbling, misfiring or even hard starting. The thicker the carbon deposit buildup on the valves, the worse the problems.
  • Spark plugs run hotter due to less heat being taken from the rear, which can escalate if driving hard for longer periods of time. When spark plug temperature exceeds 800°C, pre-ignition can occur. Melted electrodes, blistering on the insulator or yellowish colour are the most usual signs of overheating. Pre-ignition dramatically raises the cylinder pressure and can cause serious engine damage.
  • Engine with reroute

    Mazda MX-5 Miata engine with coolant reroute installed
  • Efficient cooling with front-to-back coolant flow as originally designed for B-series engines by Mazda. Proper cooling of the engine means less stress on all parts, especially during high loads. And the cooling fan will need to run less often, meaning less alternator load.
  • Even temperature on all four cylinders. Having the same conditions across the engine allows for optimal power and reliability. This way you should get even engine and parts wear and lower risk of something going wrong (assuming everything else is OK).
  • Accurate temperature reading for your engine management system (ECU, EMS) means it can deliver more accurate air/fuel mixture. This is important especially for cars with forced induction, raised compression ratios or other modifications which are more susceptible to detonation or knock. You also get the best power output, which is awesome in all cases.
  • Excellent value as a combination with better radiator or other cooling upgrades. Coolant reroute allows you to exploit capabilities of your new shiny radiator even more by putting more heat from the engine to your cooling fluid.
  • Peace of mind. Last but not least it's great to know you did a good job, whatever your tuning or driving style is. Coolant reroute is a reversible modification to your car and has no downsides if installed correctly. Even the parts we provide are reusable (except for gaskets), so you can't go wrong. It's always nice to be on the safe side.

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