1993 Ford Ranger Coolant Temperature Guage Erratic


  #1  
Old 12-18-13, 12:12 PM
J
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1993 Ford Ranger Coolant Temperature Guage Erratic

1993 / Ford / Ranger PU / 2 wheel drive / V6 engine 4.0
The temperature guage needle rises to the usual position within the normal range after warm up. About 1 minute later the needle rises to the high side of normal, rests for about 15 seconds and then drops to the lower side of normal. Approximately 10 seconds pass and then the needle returns to the usual position of normal. Somewhere between 1 minute and 5 minutes or longer the cycle runs again and continues at different intervals until the engine is shut off. Engine has never overheated (over high normal on the guage)

Actions Taken in order since start of problem follows:

Thermostat 195 degree - replaced 3 separate times

Hoses - Firm to Flexible Hard when engine is warmed up

Belt Tensioner - Replaced

Serpentine Drive Belt - Replaced

Fan Clutch - Replaced

Water Pump - Replaced

Radiator - Replaced

California Smog - Failed for High NOx at 15mph / Test results are as follows:

15mph = NOx=446 @ 369 max / HC=30 @ 64 max / CO=.15 @.48 max / O2%=0.0 / CO2%=14.38
25mph = NOx=291 @ 546 max / HC=22 @ 39 max / CO=.06 @.58 max / O2%=0.0 / CO2%=14.50

Oxygen Sensors - Replaced both sensors - left and right

Coolant Temperature Sensor - Replaced

Coolant Temperature Guage Sending Unit - Replaced

EGR Valve - does not exist

Got any Ideas as to what might need to be done short of rebuilding the engine?

Bubbles in the coolant indicating a bad head gasket do not exist
 
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Old 12-18-13, 06:44 PM
R
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Is the coolant level staying the same or do you need to add it at times? Also does it have any small oil leaks, drips on the ground?
 
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Old 12-19-13, 06:44 AM
M
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Could be a small leak in your head gasket allowing exhaust to get into the coolant system thereby causing your temp gauge to fluctuate. I would check the coolant level as Ron suggested, but even if it is fine doesn't mean there isn't a leak. Try bleeding the coolant system a few separate times after it has been running and see if you keep getting air bubbles.
 
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Old 12-19-13, 09:22 AM
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Coolant level is checked about every 3 or 4 days but have not added any coolant for over 2 months. Tried bleeding the system before replacing the coolant temperature sending unit. Since replacing the sending unit and driving the vehicle the gauge seems to be settling down. Needle does not travel as much across the gauge. I am thinking that it needs some more time to relearn its parameters since replacing the temp sensor and O2 sensors and the sending unit.
 
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Old 12-19-13, 09:26 AM
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I have not added coolant for several months except for flushing the system. I fixed a small drip at each end of the upper radiator hose after replacing the sensor and sending unit. As for an oil leak, the only one present is a small leak in the power steering hose return hose which I have not repaired yet. I am starting to think maybe the vehicle is still learning its operating parameters after replacing the sensors and sending unit. I am also planning to check out the guage.
 
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Old 12-19-13, 11:05 AM
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The engine temp gauge isn't controlled by the ECU, it only provides an input to the ECU so the fact that it is fluctuating means there is a mechanical problem. Could be the gauge itself.
 
 

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