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A temperature sending unit measures the engine coolant temperature, and is used by the ECU to adjust engine fueling and also give the driver the engine temp via the gauge on the dash
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Cooling fan will stay on if you unplug the coolant sensor. The temperature sending unit controls the gauge.Some vehicles use the same unit for both coolant sensor and temperature sending unit. Unplugging the sending unit will make the gauge go all the way to hot.replace the sending unit and see if that will solve your problem.
I guess that depends on what 3/4 is temperature-wise. Engines normally operate in the 180-210 degree F range depending on the thermostat and whether there is a mechanical or electric fan. Mechanical fans keep the temperature more stable. If you feel that after what you have done that the temperature indication is still too high, the issue may be with the sending unit for the temp gauge or the gauge itself. Have the coolant temperature checked with a second temp device if possible, otherwise, try the sending unit first and see what happens.
you are expecting the wrong temperature unit to control the fan. The temperature sender unit controls the temperature gauge and the temperature sensor unit controls the fan operation. It allows current to go to the ECM and when a pre set temperature is reached the ECM activates a relay and the fan starts . Two completely different units to do two different jobs so if it is doing what you say then there is a possibility that the wires are crossed or shorted.
check coolant level. have a compression test done to check for head gasket or cracks. If you have a viscous fan hub then replace it and check fan operation if an electric fan . Run fault codes to check for sensor faults.
on the themistat housing the top hose from the radiator hooks to this there is a sending unit on the housing replace it this is your temperature sending unit
A faulty temperature sending unit. It should be located on or near the thermostat housing. If any of your gauges reads zero, the check gauges light will come on. Sometimes even if the fuel gauge gets too low, it will trigger the light. It may be the connection at the sending unit. It may have become loose so wiggle it and make sure it is securely connected to the sending unit. If the temp. gauge needle pegs at the top of the gauge, it means the sending unit has grounded out and is faulty. If it jumps, reads off or not at all it could be a faulty sender or a bad connection.
Unplug the electrical wiring from the sending unit.
Using an ohmmeter, measure the resistance between the terminal and the sending unit's metal body
Infinite resistance or zero resistance: the sending unit is bad, replace the sender with a new one.
Other than infinite or zero resistance: continue test.
Remove the temperature sender from the engine.
Position the sending unit so the metal shaft (opposite end from the electrical connectors) is in a pot of water. Make sure that the electrical connector is not submerged and only the tip of the sending unit's body is in the water.
Heat the pot of water at a medium rate. While the water is warming, continue to measure the resistance of the terminal and the metal body of the sending unit:
As the water warms up, the resistance goes down in a steady manner: the sending unit is good.
As the water warms up, the resistance does not change or changes in erratic jumps: the sender is bad, replace it with a new one.
Install the good or new sending unit into the engine, then connect the negative battery cable.
With the engine cold, remove the ECT sensor.
Immerse the tip of the sensor in container of water.
Connect a digital ohmmeter to the two terminals of the sensor.
Using a calibrated thermometer, compare the resistance of the sensor to the temperature of the water. Refer to the sensor resistance illustration.
Repeat the test at two other temperature points, heating or cooling the water as necessary.
If the sensor does not meet specification, it must be replaced.
Submerge the end of the temperature sensor in cold or hot water and check resistance
Temperature-to-resistance relationship of the ECT and MAT sensors
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