Skip the auto shop - Our mechanics make house calls

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.

A: When a car overheats, it is an indication t...

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?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

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: HVAC is not working right

Hello. This is a programming problem. It is common on this vehicle. The HVAC module needs to be reprogrammed by the dealer to take care of this. Some of the time, the module will need to be replaced but most...

Q: Radiator fan cycles on once then never again

The cooling fan resistor if near the cooling fan connector on drivers side. The replacement of the high pressure switch for the a/c may fix the fan coming on with the a/c. Have the system computer scanned for codes and...

Q: Coolant leaking into cylinder

Hi. It sounds like you have a blown head gasket, cracked head or cracked block. Unfortunately, there is no easy remedy for this. Your engine will either require extensive repair or replacement. A trained mechanic will be able to inspect...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...
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.