Jeeper  Adventures Under the Hood  Jeeper

Coolant Temperature Switch


The Coolant Temperature Switch is located forward in the intake manifold's water jacket, on the side. It is a normally open switch that closes when the coolant temperature reaches a nominal 135° F.

Be aware that the computer will not go "closed loop" and assume control of the carburetor stepper motor until this switch closes and the Thermal Electric Switch (TES) in the air cleaner opens.

Coolant Temp Switch

- Details -

There is an easy and quick test (though not foolproof) for this switch.

Start the engine and allow it to warm up to operating temperature. The switch should now be closed. Disconnect the wiring harness connector from the switch. There should be a change in the engine's speed, indicating that the switch is working.

If there is no change, the switch may not be closing.

Connect a jumper wire across the two terminals of the harness connector. If there is a change in the engine speed now, the switch is bad.

If you have an ohmmeter, check the switch terminals. They should be open when cold, and shorted (0 ohms) when hot.

If you are certain that the switch is good, but there is no change in engine speed when it's unplugged, there may be a broken wire in the harness somewhere. This needs to be attended to, since the computer will not operate until this circuit closes.

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