Car Heater Blowing Warm Air Not Hot: Causes and Solutions

The presence of a car heater is a relief while driving in cold weather. But, malfunctioning the heating system may make the trip uncomfortable, sometimes unbearable. However, the malfunctioning issues will differ from vehicle to vehicle. You must detect the prime reasons behind that. 

This will help make the resolving process simpler. In this article, we will discuss how the heating system functions and the causes of blowing inadequately hot air. You will also learn how to fix those issues responsible for the problem. So, keep reading.

What Causes the Car Heater Blowing Warm Air Not Hot?

If your car’s heating system fails to supply air of sufficient temperature, there might be issues like:

  • Coolant issues
  • Heater core problems
  • Malfunctioning thermostat
  • Clogging of heater radiator
  • Malfunctioning blower motor

These causes are responsible for the malfunctioning of the heating system because of the mechanism of the system. Generally, the car heating system is connected to the car’s cooling system. The coolant will circulate between the radiator and the engine to absorb the engine’s heat. 

But, the thermostat valve will remain closed until the engine isn’t hot enough. After absorbing the heat from the engine, hot coolant will flow through the heater core. 

Next, a blower motor will generate airflow through evaporator A/C, hot-cold air-blending doors, and vents. After that, the air will finally reach the vehicle’s cabin.

When these issues arise, you may face symptoms like fog in the windshield, rapid coolant loss, and a sudden sweet smell inside your car. Also, the most crucial issue that will arise is the engine overheating.

Read Also: Grinding Noise From Starter: (Causes and Solutions)

Solutions Of Car Heater Blowing Warm Air Not Hot 

You should try to detect the causes of why your car’s heater is malfunctioning. Because the fix will vary according to the causes. Here are the details of those causes and solutions:

1. Coolant Issue

Coolant Issue
Coolant Issue

The primary function of coolant is to control the engine temperature and prevent the engine from overheating. Generally, coolant contains 0.5 part of water and 0.5 part of antifreeze. This mixture will control both the overheating and freezing of the heater. 

However, contamination or a low level of coolant will lead the heater to work poorly. Generally, coolant loss is one of the prime reasons for low coolant levels. Here are some common solutions to this coolant issue: 


  • Find leaks on the head gasket, radiator, or radiator’s hoses. Then, fix those leaks by sealing
  • You may need to replace the hoses or radiator if the problem is severe
  • Maintain the sufficient coolant level on the coolant tank
  • Replace the deteriorated coolant with new good quality coolant

2. Heater Core Problems

The heater cores’ main aim is to ensure the in and out passages of coolant. In addition, it is the primary function on which the defrosting and heating depend. A heater core contains numerous tubes and fins which are prone to get clogged quickly.

If somehow they get clogged, it will cause insufficient heat flow by restricting the coolant flow. 


  • Check the coolant condition and change the coolant to necessary 
  • Check the core and find leaks if the core has any. Seal the leak tightly
  • If the problem is too severe, you have to replace it. But replacing the heater core is too complicated and costly
  • Flush the heater core with air pressure or water 

Check this YouTube video to understand the flushing process better:

3. Thermostat Malfunctioning

A thermostat is a device that mainly regulates the flow of coolant. If there is an issue with the thermostat, it will lead to improper functioning of the coolant and so does the heater.

Generally, the thermostat may be stuck in two positions, open and closed. Check this picture to understand this better:

Thermostat Malfunctioning

In the open position, it will allow coolant to flow.  But if it stays in this position longer,  the coolant flow will be more than enough. Hence, your car will fail to reach a sufficient temperature.

On the other hand, a closed position won’t allow coolant flow. Here are the most common causes of thermostat issues:

  • Aging of thermostat 
  • The thermostat is not in the correct adjustment
  • Wiring issue that has a connection with thermostat 
  • A faulty water pump may lead to a thermostat problem 


  • Regular maintenance is the only prevention method of malfunctioning the thermostat 
  • Check the wires regularly and make sure there are no loose connections
  • Replacing is the best solution as the process is so easy and cheap 

Read Also: Popping Sound When Turning the Steering Wheel at Slow Speed:

4. Clogging Of Heater Radiator

Heater Radiator
Heater Radiator

Radiator clogging is a typical case in most old cars. The reason is the heater radiator usually clogs over time. When the issue arrives, the coolant can’t depart quickly through the bearings. Hence, it will lead to the blowing of insufficient hot air. Here are common causes behind the clogging radiator 

  • If the coolant is darker and thicker than in the expected condition 
  • Sometimes outside debris can cause this issue 
  • Building up of rust or scale 
  • Swallowing cooling hoses


  • The best way is the radiator flush. This means the internal cleaning of the radiator 
  • Unclog the radiator with these steps 

Step 1: First, cool down the engine

Step 2: Take out the radiator cap, and then add some radiator flush.  Try to use a heavy-duty flush(Our recommendation). It can remove heavy rust and scale formation from the radiator pretty quickly.

Step 3: Now, add water to fill the remaining space inside the radiator and close it by putting the cap on it

Step 4: Run the engine for almost 15 minutes. You can let it run longer if it seems necessary to you

Step 5: You have to open the drain valve so that the radiator flush can drain into a drain tray or bucket

Step 6: Now, reopen the radiator cap and supply clean water. Wait until you notice clean water is draining out

Step 7: After draining out of the water, fill it with coolant again 

Step 8: Start and run the engine for a few minutes 

5. Issues With Resistor Or Blower Motor

Typically, the blower motor blows hot air throughout the heater core and cabin. Any damage and defects in the blower motor will hinder this process.

Blower Motor
Issues With Resistor Or Blower Motor

As a result, the heater won’t be able to blow enough hot air. Besides, you might notice unusual sounds and bad smells coming from the blower.

These issues may occur due to the wiring problem. Also, a blown fuse or defective power relay might cause an insufficient heating issue.


  • Check the blower motor and repair the defects
  • Repair or replace the faulty wiring and ensure proper connections in the circuit
  • Change the blown fuse and repair the defective power relay

Frequently Asked Questions (FAQs) 

In this FAQs section, we will answer the most common questions about car heaters blowing less hot air.

How Often Do I Need To Flush the Car’s Coolant For A Better Heating System?

Generally, after an interval of every 2-5 years, you should flush your coolant. In other words, after every 30,000 miles, your car will need a coolant flush. This requirement may vary according to the manufacturer’s recommendation, coolant type, and environment.

How Much Will It Cost To Replace The Heater Core Of My Car?

For replacing the heater core, for parts, you need to spend around $443-$560. Besides, the labor cost will be around $588-$742. So, you will need $1,031-$1,303 for this purpose.

Can You Drive a Car If the Heater Can’t Blow Enough Hot air?

Yes, you can drive with a bad heater. But it is too risky to drive in this condition. As the engine can be overheated and end up with further engine damage, it will also lead to accidents. 


The heating and cooling systems of the car are closely related. Thus, a simple malfunction in the heating system may result in cold or less hot air inside the car’s interior. We have already discussed the reasons behind the car heater blowing warm air not hot, and their solutions.

Casuese like coolant issues, malfunctioning blower motors and thermostats, and clogged radiators are easily solvable. But problems in the heater core are slightly tricky and might be costly to fix.

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