Q: Car overheating and heater blowing cold air.

asked by on

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.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
  1. Home
  2. Questions
  3. Car overheating and heater blowing cold air.

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: What Causes a Car's AC System to Rattle When It Is Turned On?

The cause of the rattle will depend on whether it is coming from inside the car or under the hood. Typically, a rattle would be associated with the compressor and underhood components. Let’s take a look by starting under...

Q: Car overheating with new radiator

You might also have issues with your radiator cooling fan. It should spin most the time when you have your air conditioning turned on. You might also either have a clog in your system or internal engine issues. A qualified...

Q: Engine over heats no heat

If you do not have any circulation through the radiator then you may have a clogged radiator cores inside. If you used stop leak in the engine then you may have plugged up the radiator and heater core. You should...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.