Temperature gauge problem

[Keith]

89 MJ 4.0 - dash temperature gauge goes to top when key is turned on, then it drops to the bottom and stays there, changed temp sender in head, no difference. What is my problem?

[mj Mike]

their is no temp sensors on the head 89 4.0l it's the temp sending unit on the head. the temp sensor is on the engine block.

 

 

NOTE!: This is NOT the Coolant Temperature Sensor used by the ECU for engine management!

This is the temperature sending unit for the temperature guage or idiot light. It is often removed to 'burp' air from the engine coolant. Late HO engines use a 'combination' sensor in the same location as the RENIX Coolant Temperature Sensor in the block.

 

 

 

 

Located in engine coolant jacket on the driver's side of the block. To test, use a high impedance volt-ohmmeter. Resistance should be less than 1000 ohms with a WARM engine (examples = 212* would be about 185 ohms, 160* would be about 450 ohms, 100* (not warm enough) would be 1,600 ohms).

[Keith]

I guess my terminology was wrong but the problem is the same, replaced the Tem. Sending Unit in the head trying to correct a problem with the gauge in the dash, turn on key and gauge goes to top, then returns to bottom and stays there. Changing the sending unit did nothing, what could my problem be?

[HOrnbrod]

Turn ignition to RUN. Remove temp sensor wire connector from the sensor and touch it to ground. The temp gauge should go HI. If not, the circuit from the temp gauge to the temp gauge sensor on the head is open.