I was always upset that my temp gauge was staying very low. Between the low mark and 1/4 of the full scale.
What I did?
Tryed the gauge with a short, it was working.
The fuel gauge was accurate. The needle is on top when the tank is full. Ok
I understood the regulator in the fuel gauge was sending the power , abaout 7volts, to both gauges.
i undestood the screww on the regulator was used to calibrate the power. In the factory I guess it was calibrated once and then glued.
To screw clockwise gave more power to gauges, more heat and more deflection of the needeles.
My problem is the temp,sender.
I checked it in my oven wit a ohmmeter it did not meet the specifications of the FSM . To 105 degrees it is 29 ohms when it should be 23 ohms . To 100 it is 32 when it should be 27.
If I turn the regulator screw, I will make my temp,gauge more accurate but the fuel gauge less accurate.
I understand the toyota engeneers who could have used one regulator on each gauge, but found an other solution. As the range of the temp sending unit is 67 ohms, from 90 to 23 ohms , and the range for the fuel gauge is 153 ohms , 170 to 17 ohms and they deflect the same, the temp,gauge is 2,5 more sensitive than the fuel gauge.
The change of deflection of the fuel gauge will be less important than the temp gauge.
Brilliant!!
It is more impotant to check the temp of the engine than to know how much is left in the tank, as you can solve the problem with refilling when the needle is on the 1/4 low. If your temp reading is faulse you can have major mechanical troubles.
So the engeneers spared one regulator.
i surfed in the 60 section and found a guy who made e regulator for the temp gauge. An electronic card, fitted to the back of the gauge...seemed too complicated for me.
So I bought a regulator dc to dc who Change the voltage 0 to 24 volts
i disassembled the temp gauge, then cut the copper track between the output of the regulator from the fuel gauge and the temp gauge, then connected my freshly bought external regulator to the temp gauge.
Then the calibration. At 100 degrees I have measured the sending unit at 32 ohms. I disconnected the sending unit and replaced it wit a potntiometer calibrated at 32 phms, then turned the screw on the regulator until the needle goes to the place I want. Et voila
What I did?
Tryed the gauge with a short, it was working.
The fuel gauge was accurate. The needle is on top when the tank is full. Ok
I understood the regulator in the fuel gauge was sending the power , abaout 7volts, to both gauges.
i undestood the screww on the regulator was used to calibrate the power. In the factory I guess it was calibrated once and then glued.
To screw clockwise gave more power to gauges, more heat and more deflection of the needeles.
My problem is the temp,sender.
I checked it in my oven wit a ohmmeter it did not meet the specifications of the FSM . To 105 degrees it is 29 ohms when it should be 23 ohms . To 100 it is 32 when it should be 27.
If I turn the regulator screw, I will make my temp,gauge more accurate but the fuel gauge less accurate.
I understand the toyota engeneers who could have used one regulator on each gauge, but found an other solution. As the range of the temp sending unit is 67 ohms, from 90 to 23 ohms , and the range for the fuel gauge is 153 ohms , 170 to 17 ohms and they deflect the same, the temp,gauge is 2,5 more sensitive than the fuel gauge.
The change of deflection of the fuel gauge will be less important than the temp gauge.
Brilliant!!
It is more impotant to check the temp of the engine than to know how much is left in the tank, as you can solve the problem with refilling when the needle is on the 1/4 low. If your temp reading is faulse you can have major mechanical troubles.
So the engeneers spared one regulator.
i surfed in the 60 section and found a guy who made e regulator for the temp gauge. An electronic card, fitted to the back of the gauge...seemed too complicated for me.
So I bought a regulator dc to dc who Change the voltage 0 to 24 volts
i disassembled the temp gauge, then cut the copper track between the output of the regulator from the fuel gauge and the temp gauge, then connected my freshly bought external regulator to the temp gauge.
Then the calibration. At 100 degrees I have measured the sending unit at 32 ohms. I disconnected the sending unit and replaced it wit a potntiometer calibrated at 32 phms, then turned the screw on the regulator until the needle goes to the place I want. Et voila
. Everything worked so don't know why it was on. 
