Pros and Cons of Bypassing Heater Core

A heater core bypass is a common solution for older vehicles with malfunctioning heater cores. When this occurs, you’ll usually see your temperature gauge rising while driving, especially when the car is idle.

In this post, we’ll be explaining what a heater core bypass kit is, how it works, and the pros and cons of bypassing heater core.

pros and cons of bypassing heater core

What is a Heater Core?

A heater core is a part of the car’s heating system. It is located in the engine compartment and consists of a series of water-filled tubes.

When you start your car, cold air is drawn through the intake manifold and into the heater core by suction created by the vacuum in your engine. When this happens, it absorbs heat from the outside air entering through vents or windows (depending on whether you have an automatic or manual transmission). This air warms up as it passes through the heater core and continues on its way to heat up your passenger compartment.

This process creates condensation as steam dissipates from hot water flowing out of a hose connected to one end of your car’s heating system; this causes moisture buildup inside your engine compartment over time if not properly drained regularly.

How Does a Heater Core Work?

The heater core distributes hot coolant throughout the vehicle’s heating and cooling system. The core is a small metal cylinder located in the center of the vehicle’s engine. There are two tubes that run through it, one carrying coolant and the other returning warm coolant to the radiator.

When you turn your car’s engine on, it heats the coolant in the outer chamber, causing it to become hot. The heated coolant then flows into the intermediate chamber where it mixes with coolant from the inner chamber before being sent back out to circulate your car’s cooling system. This process helps keep your car at a comfortable temperature, no matter what time of year it is outside.

Benefits of Bypassing Heater Core

Bypassing a heater core allows more air to flow through the radiator into the engine, making it run smoothly and efficiently. While this might not seem like so much on its own, it can make a huge difference in fuel economy. This also reduces the chances of the engine overheating.

Another benefit of a heater core bypass is that it prevents coolant leaks. When a car’s heater core becomes blocked, it can cause the coolant to leak out of the engine and onto the ground.

This can be very expensive as it would require paying for repairs or a new engine. If you have a vehicle with a heater core that has become blocked, consider getting it bypassed instead of replacing it with a new one.

Side Effects of Bypassing Heater Core

1. Your Car Loses Its Heating Capacity

One disadvantage of using a heater core bypass is that the car won’t have any heating capacity. This can be a problem in winter and summer, but it’s particularly problematic in winter when you need to keep your car warm so you can drive safely.

2. It Makes Your Defogger Completely Useless

If you bypass the heater core, it will make your defogger completely useless. The defogger heats the windshield with hot air from a small blower behind the glove box.

The heater core distributes that heat throughout your car, so when that’s clogged up with ice or mud (or whatever), no hot air will get to your windshield and fog it up.

3. Extensive Engine Damage

Another disadvantage of the heater core bypass is that it can lead to overheating and extensive engine damage. This happens when the heater core fails, and the bypass becomes blocked, causing coolant to flow through the radiator instead of being cooled by the heater core. The coolant will then be heated up in the radiator and return to the engine, raising its temperature and damaging it.

How To Tell if Your Heater Core is Clogged

1. Weak or No Air Flow

A clogged heater core can be identified by weak or no airflow. You may also notice a damp smell or coolant leakage. Sometimes, the only way to diagnose a clogged heater core is to replace it entirely.

However, if you’re not sure whether or not your system has been affected by the problem yet, there are ways your mechanic can determine whether or not it’s worth installing an aftermarket bypass kit at this time.

2. Cold Air (Not Warm) Comes Through the Vents When The Heater is On

If you’re experiencing this issue, your heater core could be blocked. If it is blocked, it will not be able to transfer heat to the air coming through the vents. The air that comes out of the vents will therefore be cold rather than hot (if it is warm at all). This can happen for a variety of reasons:

  • The heater core has been damaged and needs replacing
  • There is debris in your car’s heating system blocking the flow of hot water from your engine to your cabin
  • Your thermostat may have failed or become stuck shut

3. Coolant Leakage Visible Inside the Cabin or a Damp Smell

If your car has been leaking coolant inside the cabin or giving off a damp smell, it could indicate water pooling in the engine and not circulating properly. This means that your heater core may be blocked. If you see coolant in your engine or undercarriage, it’s time to take your car to a mechanic.

Another way to check if your heater core is clogged is by turning up the temperature control on the dash and feeling for air coming out of the vents. If nothing comes out of any of them, there may be a blockage somewhere in the system.

How to Unclog Heater Core without Removing it

The heater core is the part of your vehicle’s heating and cooling system that distributes hot or cold air. If it becomes clogged with dirt, rust, or other debris, it won’t be able to perform its job properly.

If you’re getting ready to drive and notice that your heater isn’t working as well as it should be, you may need to unclog your heater core.

If you have access to a water hose and an air compressor, you can use these tools to push out the coolant and grime inside the core. Insert one end of the water hose into the outlet hose of your vehicle’s heater core and then, attach the other end of the water hose to an air compressor. The high pressure from the compressor will force all of the old coolants and grime out through both ends of your vehicle’s heater core.

FAQ on Heater Core Bypass

Will Bypassing Heater Core Cause Overheating?

No, bypassing heater core will not cause overheating but it will result in your car losing its heating capacity. This could be a problem for you in winter when you need to keep the car warm.

Read: Can You Mix 10w30 and 5w30?


In conclusion, there are many benefits to bypassing your heater core. It can help reduce the chances of overheating and prevent coolant leaks.

However, if you choose to bypass your heater core, be aware that your car will have no heating capacity and that it may lead to engine damage over time.

If you suspect something is wrong with your heater core, take it to a repair shop, where they can flush water or air through it so everything works properly again.