Automotive Heating System Problems

Automotive heating system problems are usually related to the engine cooling system. Hot engine coolant is diverted to the heater core through some type of heater control valve. The core itself fits inside a plastic case and has an inlet hose and an outlet hose.

Picture of stuck open thermostat

stuck open thermostat

In most cases both of these hoses are visible from the firewall on the engine compartment side of the vehicle. The inlet hose should be hot when the engine is at full operating temperature. The outlet hose from the heater core should be warm even when the blower motor is on high and the heat mode is selected. When I have a customer complaint about automotive heating system problems like lack of heat in the interior compartment in most cases I find a problem with the cooling system.

Many times I find low coolant due to a system leak. In some cases a stuck open thermostat can also cause this lack of heat condition. When the thermostat is stuck open all of the engine compartment cooling hoses will be cooler than normal.


Heating system diagnosis

Picture of heater control valve

Heater Control Valve

When there is a problem of insufficient heat it’s a good idea to begin your diagnosis with a visual inspection starting off by checking the coolant level when the vehicle is cold. You have to remember to never remove the radiator cap when the vehicle is hot.

In fact in most cases on modern vehicles there is no reason to remove the radiator cap for just checking the engine coolant level. The only time the radiator cap is removed is when the engine is cold and someone is performing a complete replacement of the engine coolant better known as the drain and fill.

All modern vehicles have a coolant reservoir tank that will have a full mark on it. You can see your owner’s manual for further instructions on where it’s located and how to top it off along with what type of coolant to use. If the fluid is at the correct level you can begin by testing for the proper engine temperature. You start the engine and allow it to warm up to full operating temperature. You select the heat position on your climate control and turn the blower on high.


Picture of infrared thermometer

Infrared Thermometer

Next you turn off the engine for safety and measure the temperature of the upper radiator hose. On most models this is the hose that leads to the engine thermostat.

The best way to measure the temperature would be with one of those fancy infrared thermometers. You pull the triger and aim the red dot on the hose and your done. These use to be really expensive but can be had for under $50 and are a very useful tool to have around.

If the upper hose is not around 150-190° then I would suspect a failed engine thermostat. If the upper radiator hose temperature is okay it’s time to move on to the hoses that feed the heater core. If the inlet hose is hot up to the heater control valve and then cool after the control valve then I would suspect a stuck closed theater control valve.


Heater blower motor problems

If you are having a problem where no airflow is coming out of the vents I have dedicated a complete page to blower motor problems. This page also includes a video that provides details on diagnosis and repair of common blower motor issues.

This video has also been posted on YouTube if you would rather go there and take a look at that video plus about six others that I have provided mainly focusing on electrical repair. Here is a link to the blower motor video. If you are looking for the latest posts on this site this next link takes you to the online auto repair blog home page.

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