Coolant gauge issue

Wilson2608

Alright guys I went home and started tinkering with the car. I opened the radiator cap (cold start) and used a thermometer to get and idea of how hot/cold the coolant is. The thermostat opens at 170 degrees(according to FSM), and at about 165-175 I noticed the coolant level started to rise in the radiator cap. At idle the temperature maxed out around 190 degrees even with me holding the rpm at 2000 for like 2-3 minutes. So it appears the thermo is alright and the coolant inst over-cooling/heating and the fans work fine even with the A/C off. So it appears everything is in working order, however I thought the coolant temp sensor controlled the opening and closing of the thermostat but it appears it does it on its own without any input from sensors.
"CO-22
< REMOVAL AND INSTALLATION >
WATER INLET AND THERMOSTAT ASSEMBLY
Inspection
INFOID:0000000004491076
INSPECTION AFTER REMOVAL
1. Check valve seating condition at ordinary room temperatures. It should seat tightly.
2. Check valve operation.
• If the malfunctioning condition, when valve seating at ordinary
room temperature, or measured values are out of the standard,replace water inlet and thermostat assembly." from FSM.

There is a picture beside it that shows a person attaching a string to the thermostat and dropping it in boiling water in order to test its operation, and there were no electrical wires connected to the thermo so it must operate without any input from sensors.

So that would explain why the everything is working besides the gauge. Like you guys suggested it appears to be that temp sensor. (if i can find the damn thing)

As for the 5v ref, all my other gauges are working properly(oil voltage time etc). Could a short in the 5v still cause this?

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Stillen G3, z1 Intake Manifold, Stillen Headers, Z1 HFC's, Stillen Catback. 330whp 267 ft- lbs tuned at Z1 motorsports.