Inaccurate coolant temp gauge fix
08-09-2014, 03:35 PM
#1
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Inaccurate coolant temp gauge fix
For those of you who have an inaccurate coolant temp gauge and don't want to mount an additional gauge for accuracy, I found an easy, cheap way to customize your temp gauge to your car's particular temperature range. Mine is a 82 5 speed 4.5L and have been told the normal operating temp range is about 190F.
I went to Radio Shack and bought a 25 ohm potentiometer (about $5). You can get them from eBay, old military stock or wherever. Just make sure it has 3 prongs and is linear.
I disconnected the larger female blade connector from the temp gauge sender and connected to that wire a male blade with a length of 14 gauge wire (16 gauge will do). I then soldered that wire to the center prong of the potentiometer.
I then soldered another length of 14 gauge wire to either of the remaining prongs on the potentiometer. (if you use the center and either of the remaining prongs, the potentiometer becomes a variable resistor. Don't only use the two outside prongs, you can't change the resistance if you do!)
Then add a suitable female connector to the end of that 14 gauge wire that will mate to the temp sensor male blade connector.
Now start your car, drive it around and get it up to operating temperature. If your temp gauge is like mine, it read over the 2nd white line when at operating temps. Make sure you use a IR gun to correctly measure coolant temps.
When the IR gun was reading about 190F (good for my 82), I just turned the variable resistor **** until the pod temp gauge showed dead in the middle of the gauge. Now that is your null setting.
I would recommend driving the car a couple of days to fine tune the resistance so you have a optimum gauge reading.
I then made a simple housing of thin sheet aluminum, drilled a hole for the shaft and mounted the whole assembly on the 14 pin cable with zip ties. I hid the wires with skinny loom and zip tied it secure.
If you don't want to mount the variable resistor, you can always measure the resistance at the prongs of the potentiometer and solder in a regular resistor in place of the variable resistor. My resistance ended up being about 16 ohms to get my gauge to center up.
Of course make sure your cooling system is operating completely normally before attempting this. Including making the mount, it took me 2 hours.
Some will say why bother? Well I'm a pilot and live and die by gauges and displays. It just bugged me that the gauge was off.
I plan on doing the same thing with the voltmeter when I remove the pod next weekend. Thankfully the voltmeter already has a POT built in.
I went to Radio Shack and bought a 25 ohm potentiometer (about $5). You can get them from eBay, old military stock or wherever. Just make sure it has 3 prongs and is linear.
I disconnected the larger female blade connector from the temp gauge sender and connected to that wire a male blade with a length of 14 gauge wire (16 gauge will do). I then soldered that wire to the center prong of the potentiometer.
I then soldered another length of 14 gauge wire to either of the remaining prongs on the potentiometer. (if you use the center and either of the remaining prongs, the potentiometer becomes a variable resistor. Don't only use the two outside prongs, you can't change the resistance if you do!)
Then add a suitable female connector to the end of that 14 gauge wire that will mate to the temp sensor male blade connector.
Now start your car, drive it around and get it up to operating temperature. If your temp gauge is like mine, it read over the 2nd white line when at operating temps. Make sure you use a IR gun to correctly measure coolant temps.
When the IR gun was reading about 190F (good for my 82), I just turned the variable resistor **** until the pod temp gauge showed dead in the middle of the gauge. Now that is your null setting.
I would recommend driving the car a couple of days to fine tune the resistance so you have a optimum gauge reading.
I then made a simple housing of thin sheet aluminum, drilled a hole for the shaft and mounted the whole assembly on the 14 pin cable with zip ties. I hid the wires with skinny loom and zip tied it secure.
If you don't want to mount the variable resistor, you can always measure the resistance at the prongs of the potentiometer and solder in a regular resistor in place of the variable resistor. My resistance ended up being about 16 ohms to get my gauge to center up.
Of course make sure your cooling system is operating completely normally before attempting this. Including making the mount, it took me 2 hours.
Some will say why bother? Well I'm a pilot and live and die by gauges and displays. It just bugged me that the gauge was off.
I plan on doing the same thing with the voltmeter when I remove the pod next weekend. Thankfully the voltmeter already has a POT built in.
