Why Does My Car Have No Heat?

How Does a Car Heater Work?

Before we dive into the details on what can cause a car heater to not blow hot air out we first need to understand how a car heater works.

The heater in your car is able to blow hot air into the cabin because of a part called a heater core.  The heater core in your car looks similar to the radiator but is typically smaller in size.  A heater core provides heat as hot engine coolant is pumped out of the engine and into the heater core effectively heating up the heater core.

As the hot coolant heats up the heater core, a blower fan then blows air over the now hot heater core which heats the air surrounding the heater core, that air is then sent into the interior of your car to warm it up.  That’s the basics of how the heater in your car works but what can cause the heater in your car to stop working

What Can Cause A Car Heater to Not Work?

Low Coolant

I know what you might be thinking, why would low coolant cause my car heater to not work?  It’s called engine coolant after all.  But hear me out.

Since your car relies on the heater core and hot engine coolant to heat it up if your car does not have enough engine coolant circulating throughout it then it won’t be able to efficiently transfer the heat from the hot engine coolant coming from the engine.

If the heat in your car is currently not working first check to make sure that the car isn’t low on engine coolant.  ****One important note, you should not take off the cap of your radiator while the engine is hot.  Doing so can cause hot engine coolant to shoot out which can result in burns all over your body.  Only remove the radiator cap while the engine is cool.  ****

Plugged Heater Core

Like I mentioned earlier the heat in your car is generated as hot engine coolant passes through the heater core which heats up the heater core.  Over time heater cores can become plugged up with debris in the coolant system which won’t allow coolant to circulate through the heater core to allow it to heat up.  To fix this sort of problem then you would need to replace the heater core or clean out the heater core to allow coolant to flow through it again to heat it up.

Blower Fan Not Spinning

Your car’s heat uses a blower fan to blow air over the heater core and then into the cabin of your car.  Over time the blower motor can short out or stop working entirely which means it won’t be spinning the fan to blow air over the heater core.  To remedy this issue the blower motor will need to be replaced with a new one to allow the fan to spin again to blow air over the heater core.

Faulty Water Pump

Another reason why your car might not have heat is a faulty water pump.  The job of the water pump in your car is to pump coolant throughout the coolant system and engine if your car.  Over the years the blades on the pump can break off or the pump may stop working altogether.  When this happens the pump would need to be replaced to allow engine coolant to pumped throughout the engine and radiator.

Coolant Leaks

Coolant leaks can also be a contributing factor as to why your car heater is not working and can result in low coolant levels.  Coolant leaks can come from coolant hoses, a bad radiator, or a blown head gasket.

Most coolant hoses are made of rubber which is prone to getting brittle, then cracking.  Radiators can also start to leak coolant if they are physically damaged or if there is a crack in the radiator.

If you have a blown head gasket it can allow engine coolant to escape as it flows throughout the engine block.  Unfortunately the only real solution for a blown head gasket is to replace the gasket with a new one which means dissembling the engine.

Faulty Thermostat

The thermostat on your car is responsible for telling your coolant system when to turn on or off based on the temperature of the engine.  But thermostats can become stuck open or closed which can keep the coolant system running all the time or not at all.

When you start up your car the thermostat will be closed which keeps the coolant system from running and allows the engine to heat up.  As your engine heats up the thermostat will then open allowing the coolant system to start running.

If your thermostat gets stuck open then it will take a lot longer for the engine to get up to operating temperatures if it gets to normal operating temperatures at all.  That engine coolant will not be hot leaving the engine which doesn’t allow the heater core to heat up.  When a thermostat goes bad it will need to be replaced with a new one designed for your specific vehicle.

Cracked/Plugged Coolant Hose

Coolant or radiator hoses are prone to cracking and can get plugged with debris from the coolant system.  If the heat in your car is not working you’d want to inspect your coolant hoses to see if they look brittle or are actively leaking coolant.

If you notice green or blue liquid underneath your car then you would want to check your coolant hoses to make sure that they are not cracked.  Plugged coolant hoses are not that easy to troubleshoot but can also cause issues with the coolant system and can cause the heat in your car to stop working.