Mazda Trucks 1994-1998 Repair Guide

Coolant Temperature Sender


The coolant temperature sender is located in the following positions:

2.3L/2.5L engine-left side rear of the engine, below the cylinder head
3.0L engine (B Series Pick-up)-top front of the engine, on the intake manifold
4.0L engine-top left front of the engine, on the intake manifold
2.6L engine-top front of the engine
3.0L engine (MPV)-top front of the engine, on the right-hand side of the intake manifold


See Figures 1 and 2

Before going to the trouble of removing the sender from the engine block and testing it, perform the tests presented in the accompanying chart to ensure that it is the sender malfunctioning, and not another part of the circuit.

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Fig. Fig. 1: Temperature gauge diagnostic chart

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Fig. Fig. 2: Temperature gauge and sending unit wiring schematic

  1. Remove the coolant temperature sender from the engine block.
  3. Attach an ohmmeter to the sender unit as follows:

  1. Attach one lead to the metal body of the sender unit (near the sender unit's threads).
  3. Attach the other lead to the sender unit's wiring harness connector terminal.

  1. With the leads still attached, place the sender unit in a pot of cold water so that neither of the leads is immersed in the water. The portion of the sender unit which normally makes contact with the engine coolant should be submerged.
  3. Measure and note the resistance.
  5. Slowly heat the pot up (on the stove) to 190-210° F (88-99° C) and observe the resistance of the sender unit. The resistance should evenly and steadily decrease as the water temperature increases. The resistance should not jump drastically or decrease erratically.
  7. If the sender unit did not function as described, replace the sender unit with a new one.


See Figure 3

Ensure that the engine is cold prior to opening the cooling system or removing the sender from the engine. The cooling system on a hot engine is under high pressures, and released hot coolant or steam can cause severe burns.

  1. Disconnect the negative battery cable.
  3. Remove the radiator cap to relieve any system pressure.