My Car Heater Only Works When I'm Driving the Car

  • Oct 1, 2021
image of a hand checking the heat image of a hand checking the heat

You pull up to a stop in your car on a cold day, and suddenly your cabin's heat turns into an icy blast. What gives? Stay warm this season by learning what could be causing your heater to only work when you drive and what you can do about it.

Why Does My Car Only Blow Hot Air While Driving?

Your car's heater works in tandem with your engine's cooling system. Many issues with inconsistent heat in the cabin can stem from coolant-relatedissues. If your car only has heat when driving, the following issues may be to blame.

You May Have Low Coolant

Coolant regulates engine temperature and the flow of hot air into the cabin. Your engine accumulates a lot of heat when working, and coolant helps to collect this generated heat by transporting it to your vehicle's radiator for cooling. 

If the coolant is low and your heater is on, you may notice that your car heater only works when driving. A properly functioning coolant system is essential to many components within your vehicle, and having no heat at idle is typically a sign that something is amiss. The first thing you should check in this instance is your coolant level. 

Caution: Never open a perceived hot or pressurized cooling system. Doing so could lead to personal injury. Check your owner's manual for how to check coolant levels or have a professional check the cooling system for you.

There are many reasons for low coolant levels, including irregular maintenance and leaks within the coolant system. Whatever the cause, it's best to have the issue inspected by a professional technician at your local Firestone Complete Auto Care

Your Thermostat is Stuck Open 

Your vehicle's thermostat helps to maintain proper engine temperature by controlling the flow of coolant out of the engine. Debris and corrosion build-up can prevent it from closing correctly. When this component is stuck open, you may experience low engine temperature. If the engine does not warm up as it should due to a stuck open thermostat, the heater won't be able to build up the warmth needed. The result: your car's heater may stop blowing hot air — idle or otherwise.

Your Heater Core May Be Clogged

While a blocked heater core is not one of the most common car heater problems, it could ultimately be the cause. The heater core uses hot engine coolant from your car's cooling system to warm your vehicle's cabin. When this component becomes clogged, you may start to experience car heater problems.

The water pump pushes hot coolant through heater hoses to the heater core. Then, the blower motor moves air across the heater core fins, allowing warm air to blow out of the A/C ducts. In some vehicles, a valve opens up and allows hot coolant to flow to the heater core when you turn on the heat. This coolant, typically around 200 degrees, then delivers the hot air needed to your car's interior. 

Your heater core may become clogged due to debris build-up. It may also start to malfunction if the cooling system is not maintained properly. When you're dealing with heater core problems, it's best to have your vehicle inspected by a professional since this component can be difficult to access (located deep behind your dash on most cars) and messy to fix.

Your Coolant System May Be Airlocked

If your heat only works when driving, this can also be caused by air pockets. Air pockets within the cooling system can prevent adequate coolant circulation and are sometimes the result of low coolant or a faulty radiator cap. 

However, low coolant levels are often the culprit in this situation and can lead to poor engine performance, overheating, and inconsistent heat (or cold air) coming from the vents in your cabin. 

Get Heat and A/C Service at Firestone Complete Auto Care 

Don't wait till the first big frost to take care of car heater problems! If your car only has heat when driving, schedule an appointment at your nearest Firestone Complete Auto Care for professional heat and A/C services.

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