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Need a Heater Core Flush? Here’s Everything You Need to Know

Heater Core Flush

There are a number of problems that can arise in your vehicle that will affect how the heat works. If you're having a problem with your engine overheating on a regular basis, or if you're having issues with no heat at all, there is a good chance that you might have a problem with your heater core. This is one of those systems that requires some routine maintenance in the form of a heater core flush. Typically, the cost of getting this type of job done by a mechanic is going to run you between $100 and $200

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As with most repairs, this is hard to pin down because it will vary based on the make, model, and year of your vehicle, not to mention where you live in the country. On the upside, flushing the heater core is the kind of job that you can handle on your own fairly easily if you are comfortable doing work under the hood of your car on your own. 


What is the Heater Core?


Your car's heater core is essentially just a small radiator that uses the heat from the coolant that runs through your radiator in order to warm up the inside of your car. When your car has reached temperature, the coolant is released to run through the engine where it picks up heat and then back to the radiator again where it will cool down. Part of that process diverts it through the heater core of your car so that you can use that heat to warm up on a cold day. 


When you turn the heater on inside your car, a valve opens that allows hot coolant to flow to the heater core. Your coolant runs through the system at about 200° or so which means it’ll be able to very quickly warm up once you've turned on the heater and activated that system.


Usually there is a blend door that allows you to mix hot air that's coming through the heater core with air from outside of the car so that you can have either hot air or warm air depending on what kind of temperature you're looking for. The same system applies if you have a dual zone climate system except in this case the heater core gets diverted into two different directions so that passengers can have their own temperature control separate from what the driver is experiencing. There are some vehicles that will have an additional heater core that controls the temperature of the rear of the car as well.


Signs of a Bad Heater Core


The heater core is a handy piece of technology when it comes to diagnosing a problem elsewhere in your vehicle. If  your car has been running long enough to get up to temperature and you turn the heat on only to experience cold air, that's a good sign you have a problem with your cooling system in the car. That's what makes the heater core a handy diagnostic tool when there's something wrong further in the vehicle. 


For the most part heater cores don't suffer too many problems as it's not a very complicated piece of technology, so it is subject to a ton of wear and tear. That said, it can occasionally fall victim to a few faults in the system. In particular, the hose that carries the coolant through the heater core May wear out over time. 


Cold Air


As we said, this is the most obvious sign that there's a problem with your heater core. If your car has been driving for a while, a good 15 or 20 minutes, long enough to get it up to temperature and you're still experiencing cold air when you turn the heater on, there's a good chance that there's a problem with your heater core.


When this happens, the temperature gauge may indicate that there is no problem with your vehicle, and it doesn't seem like there's any other problems with the cooling system at all.  As we said, this could also be indicative of a problem somewhere deeper in your cooling system so you may need to it's an extra effort into piecing this one together, or check to see if any of these other symptoms present themselves.


Foggy Windows


It's possible that you have a coolant leak in your car heater core somewhere. When that happens, especially if it is a very fine crack or leaking around a gasket, you may get a fine aerosol mist of coolant coming out of your heater and in particular when you put on the defogger. When that happens, you'll get the residue sprayed across your windows that looks like fog. Worse, it's very hard to clean off because the substance is sticky. In addition, breathing in coolant is bad for your health and can cause serious problems if it goes on for too long. Coolant is made of something called ethylene glycol and is very toxic.


Sweet Smell


If the problem is a coolant leak that's coming through your heater core, not only could you potentially notice the spray on your windows in what appears to be fog, you should notice the smell as well. Coolant has a very sweet smell and in fact a lot of animals even find it enticing enough to try to drink it. Despite the fact that the smell is rather pleasant, it's also very dangerous. 


The vapors from ethylene glycol can cause respiratory tract irritation as well as irritation to your eyes. You probably won't be exposed to enough to cause ethylene glycol toxicity the same way you would if you were to drink it, but it's still a definite health hazard. prolonged exposure could end up causing things like breathing difficulties, heart problems, kidney failure and even brain damage. You would definitely notice the problem well before that happened, but if you don't do anything about it these are potential side effects of continuing to allow antifreeze to spray into the cabin of your car while you're driving. 




There are a number of reasons that your car could potentially overheat, but if you have a leak in the heater core that means that coolant is leaking out of a line somewhere and it will likely not be properly circulating through the engine and the radiator. Over a long enough period of time the coolant levels will get so low that your car engine is unable to properly cool down. That'll mean you'll have some issues with overheating even if it's a cold day. 


Leaking Coolant


If you have a problem with the radiator then you'll typically have a coolant leak somewhere under the hood of the car and the engine compartment. This most often presents itself as visible coolant leaks around the radiator and/or hoses and puddling underneath your car when you park for a while. That's fairly easy to diagnose as a problem in that region of your vehicle.


When the problem is in your heater core itself, it's very possible that a coolant leak could still occur but instead of leaking I would around the radiator or underneath the front end of your car it will actually leak into the cabin of your vehicle. Typically, this will leak out from behind the dashboard and pool in the wells of your vehicle around the driver's feet or on the passenger side. Often it will leak from the lower vents. 


It's usually easy to tell when you have a coolant leak in your vehicle because as we said the smell of coolant is fairly distinctive, and you should also be able to recognize it by the colour of the liquid leaking into the cabin of your vehicle. For the most part, a coolant is either green or orange in color. You'll have to check for sure to tell what colour coolant you're using right now, but it's often fairly distinct and hard to mistake for any of the other fluids in your vehicle.


How to Flush Your Heater Core


The cost of replacing a heater core can be anywhere from $800 to $1,000, again depending on the make, model, and year of your vehicle. That's a pretty steep price tag and one that you don't have to pay unless it's absolutely necessary. And you can avoid having to sink that much money into this if you do a little preventative maintenance in the form of a heater core flush.


Can I Flush My Own Heater Core?


Flushing your heater core is not something every driver is comfortable doing. That said, if you are the kind of person who enjoys doing some DIY car repairs then this shouldn't be too complicated a task. In fact, this is a fairly simple job overall, and if you are comfortable doing things like replacing an oil filter or changing a tire, you may be able to handle this job without too much trouble as well. If you're not a hundred percent sure what you're doing, then there's no harm in taking it to a mechanic to get it done as well. If you feel like taking on the responsibility yourself there are just a few items you'll need to get the job done.


  • Pliers
  •  Screwdriver
  •  A three-quarter inch Barbed fitting adapter
  •  Some rags
  •  Safety goggles
  •  Gloves
  •  Clear plastic tubing
  •  A garden hose
  •  A bucket
  •  An air compressor


Locate the Heater Core: You can find the heater core in your car's firewall. It should have two hoses, one going in and one going out. Follow these back to the engine.


Disconnect Hoses:  Place the bucket underneath the heater core. You can disconnect the hoses from the firewall using the pliers to squeeze the clamps that hold them in place in the screwdriver to loosen them.  Coolant should now drain out into the bucket that you've placed underneath. Try not to miss any as this is bad for the environment and you don't want it to spill out if you can avoid it.


Hook up the Air Compressor:  Look up the air compressor to the outlet hose and seal it with duct tape or some kind of coupler. The pressure will enable you to Forsyth and he clogs or buildup that is formed in the system. You don't want to use too much pressure at this point, around 20 psi to 30 PSI should be fine to get the job done. Allow this to run for a good ten minutes to flush anything out of the system.


Connect to the Hose: After running the compressed air through until everything is cleared from the line that you can see, connect the garden hose. Turn the water on and resume flushing with water this time. Let it go until it runs clear.


Hook Up the Air Compressor Again: Run compressed air through a second time to clear out any water and Mist residue that's left in the system.


Reconnect Your Hoses: At this point you should have flushed clean everything that was in the system and dried it off as well with the compressed air. You can now reattach your hoses and clamp them back the way they were to begin with. You might want to use new clamps at this point since you remove the old ones anyway and you won't have to worry about new ones wearing out as quickly. 


Refill Your Coolant: Now you can pop open the radiator cap and refill your coolant with a 50/50 mix of antifreeze and distilled water. Again, make sure you're using the right kind of coolant for your vehicle. If you mix coolants, you'll actually create a gel-like substance that can clog up the system and cause overheating fairly quickly. Once you filled it up to the line, reseal the radiator and you're good to go. 



The Bottom Line


Proper maintenance of your heater core doesn't just ensure that you stay warm on a cold day when you're driving to work. It's a good way to ensure that you're not going to suffer any damage from your engine overheating because of a leak in your coolant system. The cost of repairing damage to your engine caused by overheating can rise to many thousands of dollars. That's definitely something you don't want to experience if it's as easy to prevent as just doing a simple flush with a hose in a bucket at home. If you notice any of the symptoms we mentioned, give your heater core flush on your own or take it to a skilled mechanic so they can diagnose the problem and get it fixed for you. 


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