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: Leaving the AC ON when switching the engine ON and OFF

Hello. All of your accessories are computer controlled and leaving them in the On position will not pose any problems. In the old days, cars were not computer controlled and would stall sometimes if you did not let the engine...

Q: Won't crank.

Depending on if you overheated the engine and it still has the cracked radiator, then you may have more than one problem. You may have a problem with the crankshaft sensor if you are not getting spark. You said you...

Q: Car overheats, but radiator full

It is possible that there is air trapped in the cooling system. Please note: never service the cooling system when the engine is hot, or the cooling system is pressurized, as serious injury can occur. Ford has a special tool...

Related articles

P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...