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What is a Heater Core Bypass? – Here’s What You Need To Know

What is a Heater Core Bypass

The heater core in your vehicle is what regulates the heat in the cabin of your vehicle. When you turn the heat on because it's a cold day, this is what allows it to keep you toasty warm. Essentially it is just a small version of a radiator and it diverts the heat from your engine coolant into the interior of the car. It's just making efficient use of your vehicle's internal systems. When you turn the heat on, it opens a valve in the heater core that allows the coolant to cycle through it that has been warmed up by your engine. A blend door in the heater core allows air flow from outside to blow the warm air into your vehicle or defog your windows as a result. And of course, you can adjust the intensity up or down to meet your needs. 

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There are a number of ways that your heater core could fail on you and start causing problems in your vehicle. When it goes seriously wrong you are going to end up having coolant sprayed up across your windshield in a way that can obscure your vision and be dangerous. When this happens it's possible to bypass the heater core so that you can keep the coolant system in your vehicle working, and allow the coolant to keep flowing without having it either pour into your cabin from behind my dashboard or springing up onto the windshield when you try to defog the windows.


Heater Core Repair Costs 


Repairing your heater core is a potentially expensive endeavour. As with any repair job this very much depends on the make, model, and year of your vehicle. That said, on average the cost of repairing a heater core can range from about $550 all the way up to $1,000. Much of that is a labor cost, which is not uncommon for most repair jobs. The cost of a heater core itself if you head to a site like AutoZone that supplies auto parts is going to be about $25 to as much as $150.


As you can see, there would be some motivation to try to circumvent this repair job if at all possible, which is why a heater core bypass is an attractive proposition to some people. Since the heater core bypass doesn't affect the overall functionality of your vehicle and in fact maintains the functionality of your vehicle when it otherwise would suffer, a number of mechanics are willing to do this job. It's also the kind of thing that you could do on your own if you check out what you need to get the job done and you're comfortable doing some home auto repair work.


How to Bypass Your Car's Heater Core


There are two schools of thought on bypassing the heater core in a vehicle. Some mechanics will recommend against it at all costs. This is not a standard procedure, and definitely the manufacturer of your vehicle would never suggest this as a solution to a problem. If you want to run your car strictly by the letter, then you're going to want to avoid doing a job like a heater core bypass. This is what you might consider a kind of a hack repair job rather than a standard one.


Is very unlikely that if you take your car to a dealership anyone there is going to perform a heater core bypass for you. That said, a private mechanic might be much more willing to get the job done although there are no guarantees there either. Not everyone believes this is the best option for you and in many cases, it could just be a stopgap to getting the job done properly.


Remember, if you bypass your heater core, not only are you preventing your cabin heater from working, you're also sacrificing your windshield defogger as well. While it's possible that you can live without heat in the cabin of your car, especially if you live in a warm climate, there are instances when your windshield was going to fog up on you. If you're unable to remove that, you either have to clean it away manually or wait it out. Driving with your windshield in that condition can be extremely dangerous. And shifts in temperature and humidity can cause it to come on quite suddenly. If you are on the road and your windshield starts to fog up and you don't have the ability to prevent it any longer, that could be a serious danger to yourself and others. That's always something you need to consider when doing a job like this.


Steps for Bypassing Your Heater Core


The process of bypassing the heater core is not the most complicated repair job that you'll ever have to do. If you've done some repairs on your vehicle already and you feel confident in your ability, you may be able to handle this on your own. If you ever doubt your ability, then make sure you're keeping your phone handy so you can consult a video that guides you through the process step-by-step so you can actually see what you need to do


 Step 1: You are going to need to disconnect the heater hoses from the firewall in your car. There should be two hoses which go through the firewall into the heater core. if you're going to bypass the coolant that means you have to divert the heater hoses from the engine to something besides the heater core.


These are the hoses that allow coolants to travel into the heater core and run out of the heater core. When you remove these hoses, you may experience some coolant leakage so be prepared to have a container handy to collect it. You don't want coolant to spill out onto the ground as this is a dangerous substance that is also quite poisonous for humans and animals.


In some models of vehicles, you may need to remove your dashboard cover to do this rather than attempt to do it from under the hood. It's possible that you can remove the great for your air conditioner to get into where the heater core is at. Again, this depends on the make, model, and year of your vehicle so you're going to have to take a look and see what works best. 


When it comes to disconnecting the hoses check to see how they are attached to your heater core. Hopefully it is just simply a matter of removing some clamps, but if they are attached differently you may have to cut them loose rather than just unclamp them. That's very unlikely, but it's not impossible. If you have to cut them, make sure you do it as close to the heater core as possible. 


Step 2:  You can connect the two hoses together using plastic tubing.  You should be able to pick up PVC tubing that is the same diameter as the heater hoses at your local hardware store. Cut a piece that's about 4 inches and smooth off the ends. You can connect the two hoses together and tighten them with clamps. You've now effectively bypassed your heater core without having to do anything to the cooling system.


You may also be able to find a hose repair kit at your local hardware store as well. This should have hose couplers or hose connectors of some kind in it that will fit this size hose to make the job a little bit easier for you.


Step 3: At this point you're going to want to turn the engine on and see how everything is functioning. Let it run for a bit to get up to temperature to keep an eye on the new hose connection is made. If it's working properly weeks from the end of that you clamp down. You can feel the hose with your hand to ensure that it's getting warm. If you're not entirely sure about air leaks a little soap around the ends of the hose can help you determine if there's any leaking coolant coming out. If you do find the leak, you may need to tighten your clamp a little more or readjust them.


If tightening the clamp doesn't fix any leaks, you may want to use some RTV silicone on the plastic connector to keep it sealed. You'll have to wait for your engine to cool down again before you do that, however. 


If everything is working properly at this point, then you have just bypassed your heater core and the heat will no longer flow into the cabin of your vehicle. If you experience any coolant leak during this process, then you're going to want to open your radiator and top up the mix of coolant to the level indicated by the line. 


The cost of doing this yourself is only a few dollars. Basically, the only thing you need to buy here is the length of hose, or that hose connector kit. You can buy a kit like that for under $6 at most auto supply stores. 


Things to Remember


No one bypasses the heater core for no reason. The most obvious reason to bypass a heater core is because you are experiencing a coolant leak of some kind. Either it is leaking from behind the dashboard onto the floor of your car, or your experience of spraying it up in a mist form onto the windshield. 


Bypassing the heater core will effectively prevent the leak from happening but it cannot undo the damage that has already occurred as a result of the leak. There is probably a fair amount of coolant or water inside the heater core already in places that it wasn't meant to get to. If you let this sit for too long it could end up corroding the heater core.


Depending on what your intentions are, having a corrosion issue in your heater core may not be a problem. If it needs to be replaced right, then obviously this won't worry you too much, but it's possible you could simply repair the heater core. If it's getting repaired rather than replaced, then you'll want to make sure it's clean and not corroding from sitting for too long unused and damp.


It's possible to prevent corrosion from forming in your heater core if you still plan to let it sit by filling it with antifreeze and then capping the ends off with some tubing that's been clamped. The heater core is supposed to be filled with coolant all the time, so if you just leave it sitting with coolant in it that could potentially prevent problems. This will only work if there was no leak in the heater core to begin with. So, you can see it's a bit of a catch-22 in this situation. If there was no leak, it doesn't really make much sense that you disconnected in the first place. If there was a leak, and odds are it will start corroding soon if you just leave it sitting empty. That's why a bypass is just a temporary solution.


 As we said, you don't need to have functional heat in the cabin of your car for it to run by any means. But it is in your best interests to have a heater that works properly in the cabin of your car because of the discomfort associated with just driving on a brutally cold day and not having heat, as well as the importance of being able to clear the fog off of your windshield. 


The Bottom Line


Bypassing the heater core in your car is a fairly easy task for a DIY mechanic to handle on their own. If you have enough confidence and skill to replace an oil filter in your vehicle that you can probably handle bypassing the heater core if it comes to that. You just need to remember that bypassing the heater core is a temporary fix to a serious problem. While the cooling system should still function well for your engine, you do need to be aware of the potential effect it's going to have in the cabin of your vehicle as well. If you live in an especially cold climate, you absolutely need to get your heater core fix rather than leave the bypass in place for too long.

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