Reply to ""Adjusting" water temp gauge"

Bob, when Ford was trying to reconcile the Italian Veglia gauge to the U.S-made sender, they used two different value resistors; first in '72, a 5 ohm 1/2 watt resistor (Tech Service Bulletin 2 article 13), then replaced in mid-'73 by a 10 ohm 1/2 watt resistor (Tech Service Bulletin 8 article 61), in-line between the sender & gauge. My "OEM" resistor was twisted into the gauge wire, under black tape- not even soldered.
The most direct fix is to actually calibrate the gauge to the car, but for safety's sake, first unscrew a 1/4" pipe plug right under the thermostat housing, horizontally in the block. Unscrew the temp sender in the tank. Interchange the two using a little pipe tape to seal. Note- too much pipe tape on the sender will electrically unground it and you'll get no or erratic readings. The stock wire to the sender in the tank will bend back & reach the sender mounted in the block. This position gives a more stable, accurate engine temp reading.
To calibrate, use an IR heat-gun on the block right near the sender and a 0-20 ohm variable resistor in the gauge line. Adjust the variable resistor so the gauge on the dash reads what the IR gun says is the block/water temp. When I did this many years ago, the 230F gauge needed an 8 ohm resistor in our '72 while the 260F gauge needed none. Never checked but I suspect the late 260F gauge has a resistor built in.