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'88 F250 7.3 temp gauge is pegged with stone cold motor. I tried unplugging the sensor (red wire front left top side of block?) with no effect. Is the gauge pegged if the wire is shorted to ground? and does the resistance of the sensor rise or fall with temperature?
In other words, if the sensor is working properly, and I unplug it, would the temp gauge go to full cold or full hot on a working circuit?
pretty sure it should goto full cold when the connector is unplugged. did you make sure that you disconected the temp gauge sensor and not the temp light wire?
Too funny, that pic is one of Dave S's from here, not sure if it's in his gallery or what, but I know it's been copied and reposted a few times.
If your engine light is on, then it could be an issue with the other sensor shown in that pic, the one just below the valve cover on the driver's side of the engine. I have one in one of the trucks right now that seems faulty, I have it unplugged and the gauge seems fine without it. Another poster had the same issue in the last few days on here too.
If you have the correct wire for the gauge and you ground it, the gauge will peg as if the engine was overheated. The resistance increases as the coolant temp decreases. That's why the gauge pegs when shorted to ground.
OK, I finally got around to driving this thing again. I unplugged the temp light sensor and the gauge reads accurately now. Do I understand this right? That sensor only illumiates the "engine" light on the dash? If I make a habit of keeping my eye on the temp gauge, there is no harm in leaving it unplugged other than I would see no red light on the dash if she overheats?