How to Perform a Heater Core Flush Like a Professional Mechanic (2023)

How to Perform a Heater Core Flush Like a Professional Mechanic (1)

All cars need maintenance, and this includes scheduled flushes to keep them working properly and running smoothly.

If you notice that your car is starting to overheat, or you notice that there’s no heat at all, something may be wrong. These are issues that should not be ignored, especially if you want your car to live a long and happy life, full of safe trips.

One way to ensure a healthy vehicle is by performing a routine heater core flush. If you don’t know what that is, then keep reading.

How Will I Know if I Need a Heater Core Flush?

There are a few telltale signs that your car needs a heater core flush. Heater core issues are unique, especially since one of those potential issues is the leaking into your interior.

Typically when heater core problems present themselves, it’s due to poor cooling system maintenance. You should be flushing and replacing your coolant accordingly with your owner’s manual. This will help to prevent the build-up of dirt, debris, and rust particles in the narrow passages—which ultimately causes clogs and damage.

Here are some of those telltale signs:

  1. Your car doesn’t seem to warm up. It runs fine, the temperature gauge reads normal, and there are no other coolant system issues. Except for the lack of heat when you turn the heat on.
  2. There’s an unknown, sweet fragrance inside your car. That’s the smell of coolant, and it’s probably lightly spraying into your interior. This is an early warning sign.
  3. Your windows fog up. If your cooling is spraying for long enough, it could coat your windows. The residue is hard to clean off, and breathing in ethylene glycol is pretty bad for your health.
  4. Something’s leaking from under your dashboard. If you notice front carpet stains or dripping from under the dashboard, it’s coolant leaking into your car.
  5. Your engine is running hot. If this is the case, check your coolant level. If it’s running low and your temperature gauge is running high, you’re going to want to get to a mechanic.

If you’re not handy with mechanics, a heater core replacement can cost up to $950 give or take. Which is why you’ll want to perform regular heater core flushes so that you can avoid the high heater core replacement cost. And breathing in poison.

Step-by-Step Heater Core Flush

A heater core flush is something that you can absolutely do yourself, even if you’re not mechanically inclined. Here’s what you’ll need to get started:

  • A large bucket
  • Clear tubing
  • Gloves
  • Pliers
  • A screwdriver
  • A garden hose
  • An air compressor*
  • A ¾” barb fitting adapter
  • rags
  • safety glasses
  • Irontite products

*An air compressor isn’t 100% obligatory, however, it is extremely helpful in loosening up any gunk before performing the flush.

If you’re using Irontite products for flushing, coating, and sealing, you’ll want to read the directions thoroughly before beginning this process.

Now, here’s how to perform a heater core flush:

Step 1: Locate the Heater Core

First thing’s first. You’re going to want to find the heater core. It will be located on your car’s firewall. There will be an inlet and outlet hose, one that takes in the coolant and the other which pushes it back out. You’ll want to trace them back to the engine.

If you’re having trouble, refer to your owner’s manual.

Step 2: Disconnect the Heater Hoses

Once you’ve located the heater core and the hoses, disconnect them from the firewall. They’re bound by clamps, which will you’ll need pliers to squeeze or a screwdriver in order to loosen them.

Before you loosen them, make sure you set your large bucket underneath. Once you’ve removed the clamps and hoses, the coolant will begin to leak out. You’ll want to catch it all and dispose of it appropriately since it’s bad for the environment.

Step 3: Apply the Pressure

If you were able to get your hands on an air compressor, now is the time to use it. You’ll want to make sure that you hook it up to the outlet hose and seal it with a coupler or some duct tape.

This will enable you to build up pressure, loosening any gunk and tough clogs. You should “pressurize” the heater core for up to ten minutes for the best results. Once enough pressure has built up, you can shut off the compressor. (Caution: Too much pressure could cause damage. Most systems can easily withstand 20 to 40psi so to be safe you don’t want to exceed that much pressure.)

Before you remove your makeshift compressor hook up, let everything drain, keeping an eye on the bucket to see that it doesn’t overflow.

Step 4: Hit it with the Hose

Once everything seems to have drained, you can remove the air compressor and attach the water hose using the same sealing method. Turn on the hose and let the flushing begin.

Once the water runs clear, you’re done flushing. Of course, you may want to repeat the entire process twice to ensure success. Once all the water has drained, you can use the air compressor to get rid of any excess water.

Step 5: Reconnect the Heater Hoses

Once you’ve successfully flushed and dried your heater core, you’ll want to reattach the hoses. It’s a good idea to have extra clamps on hand in case the old ones break. Make sure the hoses are back on properly and sealed with the clamps.

Step 5a: Flush your entire cooling system with Thoro-Flush

At this point, it’s not a bad idea to take your efforts one step further and now do a full flush of your entire cooling system using a good quality chemical flush. Irontite Products Thoro-Flush is one of the most powerful of the available flush making it a good choice to get your entire cooling system all cleaned out. Here is a good article on how to flush your car.

Step 6: Refill the Coolant

Now you can begin to refill the coolant in your heater core system. You can do this by removing the radiator cap and pouring your coolant mixture (preferably a 50/50 mix of pure antifreeze and distilled water) into the reservoir on the radiator.

This part can be a bit of a process, as you’ll have to run your car and let the coolant mixture flow through the system while also burping the coolant system. Burping will allow trapped air to be released. Air in the system can cause overheating.

Don’t Forget Your Irontite Products

Older vehicles need a little more TLC, especially when flushing the system. Irontite offers some of the best flush and sealant products on the market. This includes Thoro-Flush, All-Weather Seal, and Ceramic Motor Seal. You can use them separately, or combined for the best results.

If you have any questions about Irontite’s products or need a recommendation of which to use, feel free to contact us for our professional opinion.

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