How to completely flush the heater core without removing it. The most reliable way
How to completely flush the heater core without removing it. The most reliable way

How to completely flush the heater core without removing it. The most reliable way

The problem of a clogged heater core, oddly enough, comes up in the winter. If we have not taken too much care of the cooling system during the warm season, most likely we will have to deal with the cold air from the heater at the first frosts. However, there is a simple, reliable and inexpensive way to clean the heater core from dirt and scale.

Briefly about the theory of the heater core flushing


Any modern engine is made of cast iron (cylinder block) and aluminum alloy (everything else). The latest models from 2005-2009 are increasingly using aluminum cylinder blocks.

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At about 80-120,000 miles, the heater core can be a depressing sight. If you don’t flush the cooling system.

The heater core, as well as the main radiator of the cooling system, is made of both aluminum alloy and copper. The best models we reviewed not so long ago. However, with a careless attitude to the cooling system, and to the condition of the engine in general, the system gets clogged, scale and dirt layer is formed on the walls of channels, on the sockets, inside the heater core cells.

It is important to be clear about what exactly we need to clean inside the cooling system and the heater core in particular:

  1. Fats. These are any inclusions of oils, greases, sealants, fuels in the composition of the antifreeze. All of this settles on the walls of the system and negatively affects its efficiency. Not to mention the inability of the heater core to perform its functions – to release heat into the atmosphere or into the cabin, as far as the heater core is concerned.
  2. Salts. This is the same scale that forms on the walls of the cooling system during the heating of the engine. Almost the same story happens in an ordinary kitchen kettle. The cleaner the water, the less salts it contains and the less limescale. In the cooling system, the principle of scale formation does not change – the worse the antifreeze and the higher its wear, the more scale will be there.

It is equally important to understand that all fats can be removed with an alkaline solution, and any scale with an acidic one.

We can’t claim that all the branded coolant flushes without exception are profanity and marketing of pure water. Nevertheless, a huge part of those fluids, which are on sale and cost not cheaper than a good antifreeze, can not only be useless, but also damage the engine.

Here’s the thing. Since all deposits in the cooling system are conditionally divided into fats and salts, it is necessary to fight with each of them by different means. There cannot be a universal option, which would clean the engine from salts and fats with the same efficiency.

We came to the most important thing – how to clean the heater core and the entire cooling system as efficiently as possible. Without negative consequences.

Risks to the engine when improperly flushed


Where it’s thin, it’s torn. A simple law of life works in our case as well. Let’s assume that the flushing was successful and we removed all the grease and scale from the system. Naturally, with a well-maintained engine, and especially with low mileage, nothing bad will happen.

If the engine was not filled with the highest quality oil and antifreeze, it is likely that something will go wrong:

  1. The pump is leaking. If it happened during or after cleaning, it is worth remembering the last time the pump was changed. Most likely, its resource was already exhausted. The pump was saved from leaking only by the presence of dirt and scale on the bushing or seal.
  2. After flushing, the heater started leaking. The situation was about the same. Limescale on the cells was preventing the antifreeze from flowing out. It can also happen due to the use of suspicious cooling system sealants. We talked about the pros and cons of using them here.
  3. Leaks in hoses and connections are caused by the same reasons. The composition of the flushing fluid and the technology we offer can in no way affect the integrity of the hoses and the tightness of their connection to the thermostat housing, the cylinder head or the heater core.
  4. The head gasket was punctured. The most unpleasant story, but the root of the evil is also in the neglect of the system. The gasket was most likely already blown, but the flushing removed the fouling and deposits that stopped the gasket from blowing.

In general, if the engine before flushing was in good condition and used a good antifreeze that meets the manufacturer’s approvals, no side effects from such a flushing should not be.

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The best option for flushing and replacing the antifreeze is a vacuum fluid change stand.

How to flush the heater core without removing it from the car. Technology


We will use ordinary baking soda as an alkali. It’s great for dealing with greasy deposits like oil film. Cleaning with baking soda will be done first, because it is important to remove any hint of oily deposits. Otherwise they will not allow the scale to be cleaned.

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Limescale after unsuccessful radiator flushing.

The most effective and harmless to the engine is citric acid, which is sold at any store. Citric acid will remove all limescale, as you can be sure of when draining the engine flush. At the same time, the acid activates the metal surface and makes it susceptible, including oxygen.

That’s why flushing the system with water after acid is a gross mistake that leads to the formation of corrosion pockets on the surface of metals.

Corrosion cannot be avoided even if we flush the heater core and the entire system with distilled water. Yes, it has a minimum amount of minerals and salts, but oxygen is present in any case, and oxidation of unprotected activated metal is a direct path to corrosion.

For a complete cleaning of the cooling system of scale and oil layers we will need:

  1. A packet of baking soda.
  2. Citric acid, 200-300 grams.
  3. Bottled, not necessarily distilled, water.
  4. New quality antifreeze.
  5. Time, about 5-6 hours.

The question often arises – why can’t you just flush the heater core by disconnecting it from the cooling system, it’s easier and faster? Indeed, it is faster and probably easier. However, this version can be considered only as a temporary measure, because all the dirt and scale from the engine sooner or later will return to the heater again.

Now that we have everything figured out, let’s proceed with the flushing, strictly following the procedure and technology.

Important: Preheating and idling of the vehicle should only be done outdoors to avoid exhaust gas poisoning.

1. Drain the old antifreeze

Everyone probably knows how to drain the antifreeze in any car. The only difficulty is that we have to try to drain as much fluid as possible. If there is a separate plug in the cylinder block – drain both from there and from the heater core. There should be absolutely nothing left in the system.

2. Fill in the mixture of water and baking soda

Screw-in all plugs and taps, dilute 200 grams of soda in 10 liters of water. The proportion is calculated on the basis of the volume of the cooling system of a particular engine. It is important to remember that both the engine and the water should be about the same temperature (engine cooled, water about 20 degrees). Pour the liquid into the system.

3. Warm up the engine for 30 minutes

Start the engine and idle it for about half an hour. The engine must be in the operating temperature range for the thermostat valve to open. This is important because if the thermostat does not open, the fluid will circulate only in a small circle – cylinder block, head, heater.

To warm up the engine faster, you can put additional load on the alternator, turn on the lights or other devices, but not the heater, because it will dissipate heat from the engine. If the engine is diesel, you will have to keep the RPM a little higher than idle to warm up the fluid before the thermostat opens

4. Engine cools down, flushing with water

After a 30-minute warm-up, turn off the engine and leave it alone for an hour to allow the soda to work as effectively as possible. After a 60 minute break, drain the flush with the remaining dirt and fill with clean water.

Water is needed to wash off the soda residue, as it will neutralize the acid that we will pour in later. Let the engine run for a few minutes on water, then drain it.

5. Pouring the acid solution

When the rest of the baking soda is washed away with water, dilute 200 g of citric acid in 10 liters of water. As for the first time, let the machine idle for about 30 minutes at operating temperature.

After that turn off the engine and let it cool down also for an hour. The heating-cooling cycle (30 minutes of heating and 1 hour of cooling) is repeated 3 to 5 times, as far as you have patience. At this time the metal surface is finally cleared of scale and can actively interact with oxygen.

6. Neutralize acid with a soda solution

At this stage it is very important to flush the engine with a soda solution (50 g per 10 liters), but in no case with water. We act according to the same scheme, start the engine, warm it up for 30 minutes, then drain the solution and immediately pour fresh antifreeze. After the soda you cannot flush the system with water for the reason mentioned above, pour the antifreeze immediately.

The method we have given here is considered the safest for the engine and the heater core, and the most effective for the complex removal of salts and grease from the cooling system. Even the most expensive flushing products will hardly have a better effect.

If you follow these recommendations, the cooling system will always be clean and the heater core hot, the engine will warm up quickly in cold weather, and the interior will be warm.

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