Will Bypassing Heater Core Cause Overheating? Pros & Cons

Will bypassing heater core cause overheating? Besides answering this question, it is essential to understand this component and how it works.

This writing provides an insight into your car’s heater core and the bypassing technique. Consider the information about the pros and cons to get the best solution.

What Is Heater Core?

Heater Core
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Before digging into bypassing a heater core, it is necessary to know what it is. The heater core is an element in the vehicle’s HVAC, particularly a minor radiator connecting to the cooling system.

Once the car heater is on, there are a few hot coolants diverted to the heater core. As the hot coolant passes by, its temperature will warm up the heater.

Concurrently, a fan blows air through the heater, and the air also gets warmer.

The air released from the heater goes into the air conditioner’s vents. Thus, you can get the hot air inside the vehicle cabin that keeps you warm during winter.

Based on the name and the information above, it can be inferred that the heater core is the crucial part of the heater.

It makes use of the hot coolant from the vehicle’s cooling system to keep the driver and passengers warm.

Why Do I Need To Bypassing The Heater Core?

Can you bypass the heater core? – The answer is a big yes, and doing this can even bring you more benefits than you can imagine.

When there is leakage in the core, bypassing the heater core is essential to deal with this issue.

This cooling system radiator may form a hole over time that allows the coolant to come out once the heater malfunctions, and the temp inside your vehicle will decrease.

At this time, when the coolant is lost, the cooling system does not work as effectively as expected to carry the normal heat amount from the car engine.

As a result, the engine is overheated, leading to other issues such as damaging numerous components or wasting a lot on repair.

The formed hole also reduces the pressure inside the cooling system, which is necessary for it to run normally. Bypassing heater core is a fixing method to take up if you don’t want to replace it.

You need to remove the core and link the exit hose with the inlet connecting to the core. This process eliminates the leaking element and helps your cooling system return to normal.

Will Bypassing Heater Core Cause Overheating? Pros And Cons Of Heater Core Bypass

No, bypassing the heater core does no harm to the engine and won’t cause overheating. After this patchwork, you can keep going and avoid overheating the engine. However, you can not enjoy the heating service anymore.

Will bypassing heater core cause overheating


To begin with, bypassing the heater core has no effect on engine efficiency, for the coolant flow is even more efficient without an additional route.

The first advantage of bypassing the heater core is that it decreases the risk of overheating.

The chief cause of overheating is the heater core, and the cooling system’s radiator degrades over time, revealing a hole that leaks coolant out.

The ability to prevent coolant leaks is the next plus point. As previously stated, the appearance of a hole causes coolant to leak from the heater core.

Most people, however, are unable to discover any traces of this. So bypassing the heater core can resolve this problem.

Besides that, replacing or repairing the heater core costs an arm and leg. Therefore, bypassing the heater core is a better way to save cost than repairing it.

If money is no problem, let’s replace the heater core when it’s not operating. This way, when you want to sell the car, not only will the car’s worth remain the same, but also the heating installation is still there.

Cons – Side Effects

Of course, bypassing the heater core causes an immense drawback in which your car will not have a heat core, which means a lack of heating in your car.

It is a crucial issue if you reside in a chilly climate. It is especially vital to have a heater that operates flawlessly in your car’s interior when driving on a frosty day without heat.

However, if you live in a warm climate all year round, in California, for example, it may be insignificant.

Additionally, bypassing the heater core renders your defogger absolutely ineffective. As a result, you can not vanish the fog in the windshield and rear window since no heat escapes from the AC vents.

Although bypassing this part will prevent leaking effectively, it can’t erase the already-occurred damage due to the leak.

Inside the heater core is probably a considerable amount of water or coolant or water in places where these liquids were not supposed to go into.

If you let this sit for too long, it could end up abrasering the heater core. And eventually, your last resort is to replace the whole system.

Signs Of Bad Heater Core

Heater Is Not Working Normally

A malfunctioning heater is one of the top reasons for requiring a bypassed heater core. When there is a hole forming in the core, it allows the hot flow of coolant to release.

This coolant leakage reduces the core’s temperature. As a result, when the air flows through this component, it will not get the warmth as expected.

Another reason for making your heater core out of order is either the blower fan does not function normally, or there is an electrical issue.

In other cases, the heater core may get clogged and need flushing instead of bypassing.

There Is Coolant Inside The Car

As the heater core is located at the back of the vehicle’s dashboard, the coolant would get into the car’s interior if the core leaks.

Regarding this problem, you may find a coolant stain on the front carpets and prepare for core heater bypass.

Coolant Smell Inside The Car

It may take a certain time for the engine coolant to enter the car’s interior when there is a leak in the heater core as the dashboard is immensely sealed and prevents coolant dripping.

So the moment you sense a coolant smell is the right time to bypass; don’t wait until there are visible stains.

Another reason is that the core is lightly failed, leading to little coolant dripping. In this case, you should pay attention to the coolant’s smell.

The coolant system commonly emits a sweet smell to notify the bad conditions of the heater.

Your Window Fog Up

When the coolant leak is enough, the windows will get fogged up as the coolant is able to coat the windows with a mist.

That problem causes danger and requires a certain effort to wash off. Moreover, the main ingredient of coolant is ethylene glycol, which is harmful to human health.

Overheating Engine

The final signal to be considered is when your engine gets extremely hot and even doesn’t start. To verify an overheating engine issue, you should check the coolant level.

Suppose it has the indicator at the minimum level or the coolant level even drops below that level when you open the reservoir tank. Then, there will be a leak.

Afterward, look at the engine bay and under the car to ensure there is no more leak. If there is, the leak may be rooted in a different cooling system component, such as a failed radiator cap or a cracked hose.

How To Bypass Heater Core?

Besides the question “Can you bypass a heater core?“, “How to do this fix” is another confusion to newbies or amateurs.

In short, there are two techniques for you to apply, including removing the whole heater core and leaving this component in place while linking a PVC tube with the water hose.

Going for the first method is beneficial as the future heater core replacement will not require replacing the heater hoses.

Meanwhile, the second option is easier as the first one calls for dashboard removal. This process needs a certain amount of time, patience, and skill. If you find it hard, you’d better take it to a mechanic.


Will My AC Work If I Bypass The Heater Core?

Don’t worry, as bypassing the core will not affect the car’s AC system since it is saved with the valve. Thus, even when the heater core is not fully functional, the AC system still works as expected.

In fact, the side effects of bypassing heater core happens to the vehicle’s windshield defogger and the cabin’s heating rather than the AC.

Should I Replace Or Bypass A Bad Heater Core?

As replacing costs you a certain amount of investment, bypassing is an economical choice. However, the heater core bypass does not allow you to use the car’s heating service. Therefore, bypassing is an ideal temporary solution for saving money when the weather is not cold.


Will bypassing heater core cause overheating? You have got the fullest answer to the question.

Consider the provided knowledge to determine what is happening to your car engine. Keep in mind that this stop-gap necessitates low repair costs but still comes with some drawbacks to evaluate.

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