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Thermostat stuck open?
Faulty temp sensor or gauge?
If heat comes out of the heater, engine thermostat is ok. That will isolate it to probably the temp sensor in the temp indication system (sensor & gauge).
The cooling system should be full. Temp sensors cannot read the engine temperature of steam or empty cooling galleries.
check that the wire to the temp sender unit has not fallen off and is shorting out on the head/block. The power comes from the ignition switch through the gauge down to the sender unit and because the sender is a temperature controlled resistance unit the voltage is very low and so the gauge reads cold . as the temperature heats up , the resistance is decreased and so the voltage is increased though the gauge and the needle reads higher.. Hench if the gauge goes directly to hot on start up the wire is shorting out or the sender unit is faulty.
1st thing to do is change the thermostat. It is either missing, or stuck open (you provide good info). This is why the car is not running at operating temp and why you have little heat. The no blower for settings 1-4 probably means a bad switch.
Your overheating problems can have several possible causes.
1) Airlock in heating system - solution - bleed air from cooling system. Method is dependent on make/model of vehicle
2) Radiator blocked - solution - drain and flush radiator
3) Failed waterpump - solution - fit new waterpump
4) Engine thermostat stuck in closed position - solution - fit new thermostat
5) Electric cooling fan (if fitted) failing to operate - solution - check fan, fan operating switch, all wiring and connectors
6) Not enough coolant in system - solution - check and top up to required level. Also check all hoses for sign of leakage.
7) Faulty temperature gauge giving incorrect reading
First thing to check are the engine's thermostat. It should open around 190 degrees. Does your instrument panel have a coolant temperature gauge or just an idiot light? If the gauge is in the middle third of it's sweep, the thermostat is OK. If the gauge reads low, have the thermostat replaced. The second item to check in in the HVAC box below the dashboard. If the Fresh air/Recirculate door will not shut, cold outside air is continually mixed, which will degrade heating. Charlie