Can Bypassing Heater Core Cause Overheating? [Answered]

The heater core of your car keeps you warm in the winter. Turning on the heat of your vehicle allows the coolant to cycle through. If this coolant starts leaking we might need to bypass the heater core.

This may lead you to question can bypassing the heater core cause overheating? 

Bypassing the heater core can definitely cause overheating in your car. There are certain things that you need to ensure before bypassing the heater core. Like, check if there’s a leak or not. Also, see if the coolant is clogged or not. Moreover, refrain from byspassing when there’s a scarcity of coolant.

Don’t be puzzled just seeing the preview. We have all the details to make you understand in a simple manner.

Interested in knowing the details? Read along! 

Heater Core: Explained!

Your car’s engine has a cooling system. The heater core is one of the significant parts of the cooling system. 


The heater core is basically a small radiator. This radiator is connected to the cooling system of the engine.

The warm coolant of your vehicle will pass through the engine. This will make the heater core hot. A fan will blow through it to make the vehicle warm.

The heater core of your car will keep the cabin warm. It will also defog your car’s windows so you can see clearly.

If you live in an extremely cold environment you can adjust the intensity of the heater. 

The heater core can fail and leak because of many reasons. When it leaks, you might need to bypass the heater core.

Are you using the heater for a long time? Well, this could create a hole. Your vehicle’s coolant can leak through this hole.

If it goes on like this your car’s whole cooling and heating system will fall apart. Because if your vehicle doesn’t contain enough coolant it’s not possible to carry enough heat for the cabin. 

So you need to bypass the heater core to get through this situation. But the heater core bypass can cause overheating.

Is your heater core going through a leaking situation? Your mechanic will suggest you to replace it with a new one. 

If you’re looking for replacement heater cores then these are some of the best ones in the market-

GM Genuine Parts 15-60059 Heater CoreGet Now!
Spectra Hvac Heater Core 94559Get Now!

You might wonder if you can drive without a heater core or not. You can, but your car will start jerking when ac is on. That’s why we suggest you go for the bypass technique instead. 

You can also use the bypassing technique if you don’t have the budget. 

What Is Heater Core Bypass? 

If you don’t want to replace the heater core, another alternative is to bypass it. Bypassing the heater core is a technique to repair the heater core inside the car’s engine. This will save you some money but it comes at a cost. 


The procedure includes removing the heater core and connecting the core’s intake and exit hoses. The leaky core will be removed, and your car’s cooling system will function normally after that. 

You can perform the heater core bypass at home. All you need for it is a set of wrenches and a bypass kit. 

Here are some of our favourite heater core bypass kits:

Dorman 626-001 Engine Heater Core Bypass KitGrab Now From Amazon!
Muzzys HEATER CORE BYPASS KITGrab Now From Amazon!

However, there are some side effects of bypassing heater core. But the most common one is overheating.

Can Heater Core Bypass Cause Overheating?

Say you have successfully bypassed the heater core but the heater is not fully repaired. The holes will stay the same.

Your car will face some issues after you bypass the heater core. As you lose a great amount of coolant, the engine will start losing its cool. This will lead to overheating. 

If you are driving around with holes in your coolant system your coolant level will go down. Driving with less coolant is a big no-no.

There is a proper level in the coolant reservoir tank. You need to maintain the manufacturer’s recommended level.

Well, we cannot maintain the level of coolant as we cannot refill it. So the car’s engine will start overheating.

Bypassing the heater core is not recommended because of the overheating problems it caused.

Other Problems of a Bad Heater Core

If you bypass your heater core and it goes bad, overheating won’t be the only problem. You might notice two other problems which will make you realize your heater core has gone bad. 

Those two problems are explained in detail below-

Wet Mat

Normally when a heater core goes bad, it’s mostly because there’s a leak. And the leaked coolant will fall and make everything wet. 

Heater cores are usually mounted on the glove box of the passenger’s side. So, when that coolant leaks, it sometimes drops to the mat. 

You’ll also notice the mat is wet on some parts if your transmission cooler line is broken

Even though you know that you didn’t spill any water over there. 

And due to this, the passenger’s side might smell moldy. If mold does grow, make sure you take care of the mold properly. 

Or you’ll get that smell even after you fix the coolant. 

The inside of your glovebox might become filled with coolant too. You need to take it out and give it a proper wash to get it cleaned. 

This type of leak can also fog up your windows sometimes. In the middle of the hot summer, this will fog up your windows and windshield. 

Clogged Heater Core

Another problem that you might face is your heater core clogging up. The heat won’t come properly if your heater core is clogged up. So, you need to understand how to unclog a heater core.

When you try to turn on the heater, the heater will be clogged. So you won’t get warm air. Instead, you’ll notice ambient air coming out. 

The heater core is like a small radiator. Your ac works without heater core but instead of clowning cold air, it blows warm air. 

Make sure the temperature control is working properly. And also ensure the blower control is working properly

If you need to unclog the heater core, you must take it out first. Use a garden hose to clean it. It’ll work like a charm. 


Is It Safe to Drive A Car Without A Heater Core?

No, it’s not safe to drive a car without a heater core. In the cold winter, you won’t be able to heat your windshield if it fogs up. And a foggy windshield can easily lead to accidents. And in some weather, it might be hazardous to health. After all, the cold can sometimes become too much to bear. 

Does coolant flow through the heater core when the heater is off?

Yes, sometimes the coolant flows through the heater core when the heater is off. If you turn on the heater in your car, the heat will be generated. In some vehicles, there’s a heater valve. It directs the coolant through the heater core when it’s on. And bypasses it when the heater core is off. 

Can I Use A Radiator Flush to Unclog The Heater?

You can use a radiator flush to unclog the heater core. But it’s not that recommended. Because it’s not that useful. Using a radiator flush will only remove the rusts. But any other dirt will remain. And that’s why we recommend a garden hose. They’re strong enough to clean it perfectly. 


Now you know can bypassing heater core cause overheating. Keep the risks in mind if you’re planning on bypassing the heater core. 

One more tip before we part ways. If you want to avoid these types of overheating problems, you should replace the heater core. 

Good Luck!

Robert Lozano

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