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Can You Mix Tap Water With Engine Coolant?


Can You Mix Tap Water With Engine Coolant Safely?

The short answer is no; you can’t mix tap water with engine coolant.

Antifreeze should not be mixed with water replacing your engine coolant.

Distilled water can work, but it is not ideal.

Soft water is the best solution.

We’ll get into more detail below. 

We all know the oil in our cars must be changed, but it’s less common knowledge that the engine coolant needs to be replaced.

Eventually, the chemicals that flow from our radiator and into our engine block to prevent overheating break down and become less and less effective.

How frequently the coolant needs to be replaced will vary from vehicle to vehicle.

The standard is about every 30,000 miles or every few years.

So what is engine coolant exactly?

Engine coolant is the liquid that surges through your engine and keeps your car from overheating.

This is a tall order considering that the controlled engine explosions that move your car forward reach around 495 degrees F.

When driving continuously, these can lead overall engine temperatures up into the 200-220 degree Fahrenheit range.

To do its job correctly, the fluid that gets pumped through your engine and prevents catastrophic heat damage MUST have shallow freezing and very high boiling points.

Water alone does not meet these requirements.

We use a solution typically referred to as engine coolant to meet these specifications.

A common additive called antifreeze is used as part of this solution.

Pure antifreeze boils faster than water, but when combined, it lowers the mixture’s freezing point and increases the boiling point.

It also prevents corrosion in your engine.

Coolant is generally a 1:1 ratio of antifreeze.

Why antifreeze Water freezes at 32 degrees and boils at 212 degrees

Because engine temperatures can sometimes drop below or exceed these ranges, we must use additives to prevent the freezing and boiling of the fluids within the lines of your car’s radiator.

If that liquid were to freeze, it would break your engine.

If the fluid reaches a boiling point, it will no longer be able to serve as a heat transfer between the hot metal in the engine block, and the car will overheat.

Engine overheating causes warping of several essential components of the machine, like the aluminum cylinders, engine head gasket, and water pump.

When water mixed with antifreeze is primarily made of ethylene glycol, the freezing point is bumped down to -35 degrees, and the boiling point is raised to 223 degrees Fahrenheit.

This makes ethylene glycol the perfect additive to our cooling system!

So now we know that mixing antifreeze makes a suitable concoction for heat transfer within the car’s cooling system.

Still, we need to be specific on exactly what water to mix with the antifreeze should not be mixed with water replacing your engine coolant.

Please save yourself the trouble down the line.

Do not use tap water when it comes to your vehicle.

While some engine coolants are designed to be mixed with water before being poured into the cooling system in your car, you cannot just use any water you please.

Tap water contains minerals that will eventually form deposits inside your radiator, plumbing, and water pump.

This is also referred to as the hard water scale.

This is all types of tap water we are talking about here, no matter where you live! Tap water has mineral deposits in it by nature.

You can’t put these minerals in your cooling system without causing problems.

When tap water is repeatedly used in your cooling system, you will start to get a buildup of calcium and magnesium.

This build-up is also referred to as a hard water scale, and you’ve likely seen it on your household appliances.

When your radiator gets mineral buildup or hard water scale, it becomes less effective at cooling off those hot engine parts.

And even just a little build-up is a huge problem.

A 1/16-inch hard water scale will make your cooling system 40% less effective.

That means your engine can get 40% hotter than it should, which can cascade into many other engine-related issues.

A less effective cooling system can lead to your engine overheating.

When your engine overheats, it can, and if untreated, will cause damage to your engine.

Some engine parts will warp with the heat they are not meant to withstand.

Common parts that break and require repairs after engine overheating include a cracked head gasket (average replacement cost $1500), warped cylinders (average replacement cost $500), and water pump replacement ($350- $700).

It is much cheaper to be proactive and replace your coolant with the proper ingredients before negligence or laziness leaves you without the convenience of your vehicle because it is in the shop undergoing a costly repair.

Since you are reading this article, it’s pretty; you’re likely to replace your coolant yourself.

It will probably cost you around $30 to complete this project.

With the average cost of coolant repair at the mechanic being about $130, you’ll be saving save$100 in labor costs from the mechanic.

Go you!!

To reiterate.

Tap water inside your engine block is terrible!

Do not mix your antifreeze and tap water.

Distilled Water Isn’t The Answer Either

There’s a lot of information on the internet that recommends using distilled water when it comes to the cooling unit in your vehicle.

I’ve even seen a famous mechanic put water into his cooling system!

The thought on the YouTube process here is that distilled water has stripped the minerals from it and will not leave build-up deposits in your hoses and radiator.

While this is good in theory, this does not take into account the distillation process.

Here’s why you should NOT use distilled water.

When distilling, the water is heated into a gaseous phase.

When this water boils off and evaporates, it leaves behind the calcium and magnesium that once lived between its molecules.

This process is called mineral stripping.

While we need water that has been removed from these minerals for the coolant system, the distillation process will leave the water ionically imbalanced.

Essentially the distilled water solution is unstable because it is missing an electron.

Distilled water will damage the metals in your engine if used repeatedly.

The Science Behind Why This Works

As the water evaporates, the calcium and magnesium take with their electrons, leaving the remaining solution yearning to rebalance itself and gain a complete set of eight valence electrons.

When you put distilled water inside your engine block, it will do its best to strip electrons from the metals it comes in contact with.

Essentially the gist of this without all the subatomic jargon is that distilled water is still damaging to the components of your engine, just in a different way than tap water.

So steer clear of distilled water and tap water despite what most people post online.

Use Softened Water For Best Results

Softened water is the answer here – it makes a difference.

The process of water softening takes tap water and removes the minerals within it.

The main minerals in tap water are calcium and magnesium, and there are also trace amounts of iron, depending on where you live.

Softened water, like distilled water, is free of calcium and magnesium.

However, the process of removal of these minerals is vastly different.

And that makes all the difference.

Here’s why.

The significant distinction between these processes is as minerals are removed in the softening operation, they are replaced with a sodium ion.

The solution that results here is stable; it’s not; it’s to take electrons from substances it comes in contact with.

This makes softened water safe to use, as it won’t destroy the internal systems of your vehicle.

Softened water, unlike distilled water, won’t strip the metals in your engine block of their electrons, which can cause damage to your engine.

With the average engine repair cost of around 3,500 dollars, it pays to be prudent.

Be prudent and spend the extra time getting soft water next time you need to repair your car.

Softened water is safe to put in your engine and won’t cause damage, unlike tap water or distilled water. So be smart. Stick to soft water!!

You Can Either Make Soft Water Yourself – Or Buy A Water Softener

So now that you’re aware of the facts, have soft water to mix in with your antifreeze and where you can get it.

  1. From your tap, if you have a water softener. You can get one of these from Amazon/Home Depot/Walmart.
  2. You can make your own using the process detailed below
  3. Ask your family or friends who live nearby if they have a water softener system installed in their homes. If they do and agree to give you some of their water, you can bring gallon jugs or another water transport container and fill them up from the tap at their home. I would verify that the water is softened.

Unfortunately, from my research, I haven’t found soft water bottles you can purchase online.

What I did find was distilled water claiming to be soft being retailed.

Please don’t buy distilled water pretending to be soft water.

There is a difference, don’t let the water companies fool you by claiming they have soft distilled water.

LUCKILY you can make softened water pretty quickly at home. Here’s how.

How to make your softened water without installing a water softener in your home

  1. Bring your water to a boil.
  2. Next, allow the water to cool. If your water is temporarily hard, meaning it contains bicarbonate and calcium ions, then you are good to go, and the boiling process will fix this problem. For most of you, the water is permanently hard; in other words, it contains calcium and magnesium sulfates. If your water is permanently hard, proceed to step two once the boiled water has cooled.
  3. Add washing soda to your water. Washing soda, similar to baking soda, can be found and purchased at most large retailers like Walmart or Target in the laundry section. For exact mixing proportions, check the packaging of the washing soda.

Coolant or Antifreeze – Which Should I Combine With My Soft Water?

Antifreeze and engine coolants are used interchangeably.

However, they are not precisely the same thing.

Let’s clear up this confusion.

Engine coolant refers to the liquid mixed solution that surges through your car’s engine block, keeping it from overheating.

Essentially precisely as its name describes.

It is important to note that it is a solution of several substances.

Antifreeze possesses a chemical; ethylene glycol is found in most premixed engine coolants, ready to be added to your vehicle.

It is also sold separately as a pure substance ready to be mixed with SOFTENED WATER and then funneled into your car’s cooling system (after you have read the manufacturer’s instructions and safety warnings).

To reiterate, your options here are to purchase a premixed engine coolant ready to be added to your car’s empty, clean engine coolant compartment. Or you can buy antifreeze in a 1:1 ratio with softened water.

Always read the mixing instructions to verify safety procedures and mixing ratios which may vary from brand to brand.

I have included some information in this article to help you clean out your engine coolant system of all old, used, and dirty coolant and to help you dispose of it properly.

REMEMBER, antifreeze has to be disposed of properly!

Please be sure to keep your users and replacement coolant away from animals.

It tastes sweet to them, and they will drink it.

You Don’t Have To Mix All Coolants With Water

Now that we understand the fundamental differences between engine coolant and antifreeze, the rest of the article is much more manageable.

Some engine coolant will be premixed from the store and ready to be added to your vehicle.

It does not need to be added to water.

If you are unsure if you have purchased a premixed engine coolant, check the instructions on the label.

To determine what engine coolant your car requires, refer to your car’s owner manual.

Generally, your car will also be labeled near the fill spot, showing what engine coolant color is recommended.

They are traditionally green or orange.

Antifreeze is a substance that does need to be mixed with equal parts water to make a proper engine coolant.

What type of water, everyone??


Please check the manufacturer’s instructions when mixing antifreeze and adding the fluid to your vehicle.

Be sure to follow all safety precautions detailed by the manufacturer as well.

Remember that this stuff is toxic and can kill mammals that drink it.

Why Do We Add Antifreeze To The Water We Use To Cool Our Engine?

  1. Water is corrosive and will eventually corrode the engine and cause rusting of the internal components it comes in contact with, making them unable to do its job.
  2. Water has a relatively low freezing point, but in most areas of the world, winter does get cold enough to bring fresh water to solid ice. If this were to happen within a vehicle, it would break the engine.
  3. Coolant also keeps the water from boiling when it gets too hot. When engine coolant boils, or any other liquid, it cannot get any hotter while in the liquid form. This means it is no longer effective at receiving heat from your engine or cooling anything down.
  4. Coolant protects your car’s cooling system when driving in extreme weather climates. So if you’re planning on adventuring towards the poles in your vehicle or driving through death valley, you should ensure your car’s coolant levels are full and have been mixed with the appropriate coolant for your car.

What Happens When You Add Water To Antifreeze?

The properties of water shift when forming a solution with antifreeze temperature at which its boiling point increases.

This makes it better at withstanding heat and, in turn, improves its ability to cool down what it comes in contact with.

Water is an excellent conductor meaning it receives energy, or heat, well.

When you add antifreeze mix, it becomes even better at conducting because the boiling point increases.

Essentially the liquid solution can retain more heat before converting into a gaseous state.

In layman’s terms, here is the antifreeze solution to cool down the hot engine parts when it runs through your engine blocks.

Antifreeze carries several additives that reduce the solution’s corrosive effects.

These additives may include but are not limited to sodium silicate (an aluminum anticorrosive) and antifoaming agents.

You always want to read the manufacturer’s instructions to see how and if you should mix the coolant with water.

It’s also important to note that antifreeze is dangerous to animals.

It is enticing to dogs and cats because it tastes sweet to them.

They will try to drink it if given a chance, and it is usually deadly.

Make Sure You Dispose Of Your Antifreeze Properly

Be careful with your used engine fluid during the removal process, as it is toxic and should not simply be dumped out with the trash or down a drain.

It needs to be disposed of properly. Be sure to transfer the liquid into something watertight.

It needs to be in a container that will be feasible to put in your car to take in for recycling.

Used engine coolant can be appropriately disposed of pretty quickly.

Most mechanics will take it off your hands for free (they make money when they sell it off to the disposal companies).

You can also recycle the fluid at your local disposal center or hire a private waste disposal company to pick it up.

I reiterate here engine coolant is toxic.

We do not want it in our water systems, pets, or children.

That would be not good.

So be responsible.

What Type of Engine Coolant Should I Use?

Wouldn’t it be lovely if most car manufacturers used a consistent type of engine coolant?

Well, they don’t and I recommend checking your car’s user manual to find the manufacturer’s recommended type of engine coolant.

From there, you can choose a brand or generic from this category of coolant.

There are three standard engine coolant varieties: inorganic additive technology, organic acid technology, and hybrid organic acid technology.


This solution is outdated and less superior to its competitors nowadays.

As there are now more effective options on the engine coolant market, you typically only see inorganic additive technology in older vehicles.

If your car uses this engine coolant, you must stay on top of flushing your system and replacing your coolant.

Inorganic additive technology coolant must be changed every 24,000 miles or two years, whichever comes first.

This is far more frequent than newer coolants that are on the market.


The next coolant we will discuss is much more with the times and requires far less maintenance and upkeep.

It is increasingly popular in vehicles newer than the year 2000.

Organic acid technology coolant, widely used by General Motors, only needs to be changed every five years or 150,000 miles!

That is a remarkably long time that you can go without replacing your coolant.

This saves these car owners time and money involved with maintenance procedures.

This variety of OAT coolant is traditionally orange-yellow, but not always. 

It is derived using fully neutralized organic acids and azoles, which are the components that make the fluid anti-corrosive.

This is also where the substance received its name.


Finally, we have Hybrid Organic Acid Technology, a slight variation of Organic Acid Technology.

Both of these coolants have essentially comparable replacement cycles

Change The Fluids In Your Cooling System Every 30,000 Miles

Eventually, the chemicals in antifreeze break down and become less effective at keeping your car’s temperatures moderate.

When this happens, your car is at greater risk of engine overheating, which can lead to costly repairs.

It’s best to be proactive here and change this antifreeze every 30,000 miles or so for most vehicles.

Your car’s user manual should make a recommendation on this mileage specific to your vehicle in the same section where they detail what

What The Color Of Your Antifreeze Means

Until very recently, the most commonly used color of antifreeze was green.

This is because this is the color associated with the variety of coolants called Inorganic Additive Technology or IAT.

IAT has been on the decline as the choice of car manufacturers simply because there are now more effective coolants on the market

Increasing in popularity are orange and red coolants, typical of the Organic Acid Technology variety of coolants.

While these types of coolants are traditionally these colors, you should always verify that you are using the proper coolant for your car using your vehicle’s owner’s manual.

Nowadays, coolant color doesn’t mean as much as it used to.

The purpose of companies who manufacture engine coolant dying their products is for marketing purposes as well as safety concerns.

Antifreeze is typically bright green.

It does a couple of things by making it a ghastly bright color.

It makes the substance easy to identify when compared to water.

This is super important because, remember, antifreeze is toxic.

It could be deadly if you, your family members, friends, or your animals were to drink.

Contact a poison center or go to the emergency room if you think you’ve accidentally consumed this stuff.

Antifreeze can add whatever color dye they would like to their product.

For this reason, I encourage my readers not to use color alone to distinguish the variety of antifreeze good for your car.

Can you use battery water as a coolant or other substitute?

It depends on what you consider to be “battery water.”

Some individuals refer to battery water when talking about the liquid within car batteries called an electrolyte.

An electrolyte is a mixture of sulfuric acid and pure water.

It should never be added to the coolant system in your car.

Please do not drain your battery into your cooling system.

To others, the term battery water refers to the water you add to your battery.

This water is just distilled water.

Putting distilled water in your radiator is a generally accepted practice.

However, I encourage people to opt for soft water over distilled water.

I reason that soft water has a complete set of valence electrons, whereas distilled water does not.

That means soft water will not strip the metal in your engine block in the same way that distilled water will.

If you are confused by this, I cover more on the science behind distilled water and soft water towards the beginning of this article.

Opt for soft water over distilled water.

Whatever you do, though, won’t drain battery fluid into your car. I’m willing to bet it will go poorly for you and your vehicle.

How to safely and effectively drain and flush your cooling system

Most of my readers are interested in engine coolant because they are actively undertaking the replacement of their engine coolant themselves. This is awesome and will save you guys some money.

However, you must ensure that you replace the fluid correctly and responsibly dispose of your old coolant.

  1. SAFETY. Cooling systems are pressurized, and you must ensure you use your car when the engine is excellent. We don’t want you scalded by super hot engine coolant, okay? Please pay attention to these warnings he gives you.
  2. Before flushing your engine’s cooling system, what preparations do you need to make? Generally, it is suggested that you use a chemical coolant flush for several days before actually flushing your engine.
  3. The section in which you can look within your owner’s manual for information regarding what engine coolant you should personally use for your car.
  4. How to disconnect and reconnect the hoses in your car’s cooling system so you can attach a hose and flush the system.
  5. How to ensure the engine cooling system has been drained entirely.
  6. What to drain your old cooling fluid into.
  7. Safe handling and disposal of used engine coolant.
  8. He even shows you the change in color with each of his five or so engine flushes!
  9. Finally, the video shows him replacing the engine coolant with a new coolant.

Coolant Leaks Can Be An Expensive Issue – So Change Your Vehicles Antifreeze and Engine Coolants Regularly

Car repairs can be absurdly expensive, and you can expect those unexpected repairs before too long no matter what vehicle you drive. 

If there’s an issue with your engine coolant, it could cause significant damage to your engine. For most vehicles, a new engine can cost up to $5,000.

If that seems absurd to you, luckily, you aren’t alone.

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