Side Effects of Bypassing Heater Core & Advantages

The heater core distributes hot coolant throughout the vehicle’s heating and cooling system. A heater core bypass is a common solution for older vehicles with malfunctioning heater cores. The purpose is to allow more air to flow through the radiator into the engine, making it run smoothly and efficiently.

There are pros and cons of bypassing the heater core and I’ll be explaining them in detail.

Pros 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.

Cons 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. Your Defogger Becomes 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.


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.