Mazda Trucks 1972-1986 Repair Guide

Thermal Reactor


See Figure 1

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Fig. Fig. 1: Thermal reactor cooling circuit

A thermal reactor is used in place of a conventional exhaust manifold. It is used to oxidize unburned hydrocarbons and carbon monoxide before they can be released into the atmosphere.

If the engine speed exceeds 4,000 rpm, or if the truck is decelerating, the air control valve diverts air into passages in the thermal reactor housing in order to cool the reactor.

A one-way valve prevents hot exhaust gases from the flowing back into the air injection system. The valve is located at the reactor air intake.


Perform thermal reactor inspection only after the reactor has cooled sufficiently to prevent the danger of being severely burned.

  1. Examine the reactor housing for cracks or other signs of damage.
  3. Remove the air supply hose from the one-way valve. Insert a screwdriver into the valve and test the butterfly for smooth operation. Replace the valve if necessary.
  5. If the valve is functioning properly, connect the hose to it.

Remember to check the components of the air injection system which are related to the thermal reactor.


Thermal reactor removal and installation are given in the Engine Mechanical section of Engine And Engine Overhaul .