A pretty reasonable assumption would be the thermostat is stuck open.
on the side of the radiator
Yes.
your float could be stuck
1990 Chevrolet Lumina temperature sender is located on the back side of the thermostat housing. The sender has a wire that goes to the temperature gauge.
It's a GM
Check for power and ground at the tank. If it is okay then the sending unit is most likely the cause.
Yes it can depending on driving conditions.
check ground first
The sending unit is either defective or it is hanging on something in th tank.
Install a manual gauge to check actual pressure or try Replacing oil sending unit
Check actual engine temperature with a thermometer--if in acceptable range temperature sensor or gauge may be defective
Take wire off temperature sender look a guage. If guage at cool, temp sender needs replacement. If guage still at hot, temp sender wire shorted to engine or vehicle body.