This is a pain, You have to bleed the air out of the system. There are two bleeders. one on the thermostat housing and one on the tube coming out of the water pump.
Bring the car to operating temp, shut off, and open the therm. bleeder until you see coolant(be careful). Do the same with the the other until all air is out.
I actually use a small 12v pump to circulate the coolant(cold of course) through the intake. Take the rubber hose off the tube at the water pump connect the pump inline and pump unitl you have no air bubbles.
on the side of the radiator
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.
Yes.
your float could be stuck
Its in the gas tank with the sending unit and fuel pump
Temperature gauge may drop when heater turned on because additional coolant from heater core is introduced to cooling system - usually this coolant is cooler than what is currently circulating
It could be that your heater core is blocked or damaged somehow.
Most likely the oil pressure sending unit is defective, replace.
This would indicate that the system is low on coolant when the gauge is hot. Not enough coolant to service the heater core.
Try changing the temperature sending unit. If the guage is "pegged" while the key is off, you have a bad guage.
Input pressure.
The gauge is part of the fuel pump/float assembly within the gas tank. It is probably a $500.00 repair. It is harmless.