Q: Car overheating and heater blowing cold air.

asked by on December 28, 2015

The engine is overheating. Probably just needs a new thermostat. The heater is not blowing hot air either.

When a car overheats, it is an indication that there is a problem with the engine cooling system. The purpose of the engine cooling system is to keep the engine at a temperature that is consistent. If the temperature of the engine becomes too hot or too cold, the engine cannot perform well and extreme hot or cold temperatures can cause damage to engine components.

The water pump takes coolant from the lower radiator tank and pumps it through passages to cool the engine. The directional flow of the coolant is to the engine block, cylinder head, and then to the radiator outlet. Along the way, the coolant picks up heat and as it flows back to the radiator. When the interior heat is in use, some of the hot coolant flows through the heater core and the blower sends heated air through air vents to provide the interior with heat.

The rest of the hot coolant is regulated by the thermostat, which maintains a consistent engine temperature that does not rise above or fall below the engine’s normal operating temperature. If the engine is too hot, the thermostat will open to allow the flow of coolant into the radiator. The radiator will then cool it down before it is pumped back through the engine block by the water pump.

If any of the engine cooling system components are damaged, this will cause the car to overheat. The following are some possible problems that may occur with the engine cooling system:

  • Engine cooling system leaks
  • Low levels of coolant
  • A faulty thermostat (thermostat that is stuck in the closed position)
  • A blockage in the coolant passageways
  • A faulty radiator
  • Worn out radiator hoses
  • A faulty radiator fan
  • A faulty water pump

If the heater is blowing cold air and the car is overheating, it is likely that the problem is related to the engine cooling system as well. The following are some issues that may be causing the heater to blow cold air:

  • Low coolant levels
  • A plugged/clogged heater core
  • A faulty thermostat (thermostat that is stuck)
  • Broken blower and/or blower motor
  • Heater core bypass hoses that have leaks
  • Heater core bypass hoses that are worn

If your car is overheating and/or your heater is not working, it should be inspected and diagnosed as soon as possible to avoid causing damage to the engine and the inconvenience of operating the car under this condition.

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