PC Water Coolant Chemistry - Part II

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Welcome back to the second part of our article on PC water coolant chemistry! If you have not already done so, please check out Part I for detailed information on some of water’s unique physical, thermal and chemical properties and the various types of water available for use in PC water-cooling systems.

In Part I, we discussed some of water’s unique properties (thermal conductivity, specific heat, viscosity, etc.) that make it an excellent coolant for use in water-cooled PCs. We looked at several different types of water (tap, distilled, bottled, DI) and concluded that distilled water or purified drinking water were two potentially good sources of water that were easily obtainable.


Chemicals for Water Cooling


We also noted that most anything you add to water (antifreeze, corrosion inhibitors, windshield wiper fluid, etc.) will decrease water’s overall thermal properties. So why not just use pure water as a coolant? That question brings us to Part II.

Pure water might initially appear to be an excellent coolant for use in PC water-cooling systems. Unfortunately, pure water also has a few undesirable properties. These include:

  • Pure water is corrosive to metals due to the very low dissolved solids content (ions)
  • Water promotes oxidation of metals also known as corrosion
  • Water typically contains small quantities of various microorganisms, which may grow and multiply over time

In Part II, we will take a closer look at the suitability of using pure water, discuss corrosion, summarize some of the many water additives that are available, and present several popular recipes for coolant mixtures. Here is a brief outline of what we will cover:

  • Too Pure?
  • General and Galvanic Corrosion
  • Water Additives (surfactants, corrosion inhibitors, antifreeze, biocides, etc.)
  • Maintenance
  • Basic Coolant Mixtures
  • Conclusions

Too Pure?

Can water be too pure for use in PC water-coolant systems? It may sound counter-intuitive, but yes, water can be too pure. As we discussed in Part 1, both distilled and de-ionized (DI) water have a very low dissolved solids content. This means there is a very low concentration of ions in the solution, as indicated by high conductivity. It takes a lot of effort and energy (various purification processes) to remove the majority of ions from water. Water desires these ions back to maintain equilibrium and will aggressively take them from any available source.

Using 100% distilled water or DI water in a PC water-cooling system is not recommended, as it may slowly attack metallic surfaces, especially aluminum!

Several of the coolant additives specifically designed for race cars and water-cooled motorcycles have warnings stating not to use distilled or DI water with their products unless automotive antifreeze is also used in the mix. The reason for this is that the thin walls of lightweight aluminum radiators used on racing cars and motorcycles may form pinhole leaks as the aluminum is attacked by the hot, pure water. Adding a little antifreeze (or other additives) to the mix puts enough ions back into the water to re-establish equilibrium and help neutralize pure water’s corrosive properties. It is worth noting that this effect is greatly accelerated by the higher temperatures found in racing coolant systems.

So why use distilled water at all? Another good question! The two main reasons I recommend using distilled water as the primary component of the coolant are:

  • Distilled water is naturally low in dissolved minerals and other contaminants
  • Steam distilled water (especially if it has been treated with ozone or UV light prior to bottling) will be virtually free of microorganisms
  • And, because the corrosive nature of distilled (or DI) water can be effectively neutralized by adding small amounts of various additives

Using water that is low in mineral and other contaminants is important for two reasons: First, having a low mineral content will help prevent any mineral deposits from forming on heat transfer surfaces. This is the same scaly buildup commonly associated with hard water. The second reason for using water with minimal contaminants is that this removes one of the main food sources that microorganisms need to live on. Without a food source, they can not grow and multiply.

As in Part I, I still recommend using distilled water as the primary coolant. The key is to use a proper mix of additives to minimize corrosion, keep microorganisms from growing and decrease surface tension. We will discuss various coolant additives in more detail later.


Metals corrode on contact with water. General corrosion is the primary means by which metal components are attacked, causing the deterioration of metal surfaces. Corrosion is an electrochemical process known as oxidation. When metals are exposed to a water environment, they oxidize. During oxidation, the metal surface will begin to slowly dissolve, releasing metallic ions into the water. At the same time, free electrons accumulate in the metal. All metals have a tendency to oxidize – some faster than others. If not prevented, corrosion can rapidly degrade a system’s performance due to decreased heat transfer across corroding surfaces and in the worst cases lead to component failure.

The three most commonly used metals in PC water-cooling systems are copper, brass, and aluminum. Copper is used to make waterblocks, radiators, and rigid tubing. Brass fittings are frequently used throughout water-cooling systems for attaching flexible tubing to components and brass tanks are common on many radiators. Some waterblocks and radiators are made out of aluminum. Unless protected by special coatings or water additives, aluminum components will rapidly corrode when used with other non-aluminum parts, such as copper and brass. Most pond-style pumps are made from plastics, which are not affected by corrosion.

Aluminum has a much greater tendency to corrode than does copper (defined by its position within the galvanic series). When dissimilar metals are used in the same system, an electrolytic cell is created, which will promote galvanic corrosion. Ideally, only copper and brass components should be used in a PC water-cooling system, but that isn’t always possible. Many of today’s popular waterblocks incorporate a copper base, aluminum water jacket, or top plate and brass fittings.

Copper has good thermal characteristics and is quite resistant to general corrosion in water at room temperature. Copper is more expensive to purchase and more difficult to machine than aluminum. That is why copper waterblocks and radiators typically cost a little more than aluminum ones. This is also why you won’t find pure copper fittings. Zinc is added to copper to form the alloy brass, which is much easier to machine and make parts from than pure copper.

The following pictures illustrate the effects of corrosion on dissimilar metal parts. I placed two small blocks of aluminum and a short piece of ½” copper water pipe into a Tupperware container filled with water. This is the type of corrosion you might expect to see in 6 months to a year in untreated water when using a combination of bare aluminum and copper/brass parts.





Notice how much more severe the corrosion is on the aluminum block on the right – it is in direct contact with the copper tube, allowing an electric current to flow (battery effect) and promoting galvanic corrosion. The metal pieces are slowly dissolving (especially the aluminum ones) and the water is turning cloudy from the buildup of corrosion products.

Here are two more pictures showing the accumulation of corrosion products and the surface pitting caused by the corrosion:


Galvanic corrosion occurs when two dissimilar metals are electrically connected while immersed in an electrolyte (water). Galvanic corrosion is one of the most aggressive forms of corrosion and can be one of the most destructive. Incorporating copper and aluminum components in the same system sets the stage for galvanic corrosion to occur. Wetted metal surfaces will slowly dissolve and may eventually cause structural failure. Numerous deposits from the deteriorating aluminum will gradually coat other internal surfaces, especially the copper waterblock. Over time, this can dramatically reduce thermal transfer and decrease cooling efficiency. Corrosion products may precipitate out of solution and block micro-channels in the waterblock and radiator.

The best way to prevent galvanic corrosion is to ensure that all metal parts used in a system are the same. If dissimilar metals are used, they should not be electrically connected (such as through a common chassis ground) but instead should be electrically isolated from one another. The addition of corrosion inhibitors will help slow down the effects of galvanic corrosion when more than one type of metal is used. Let me repeat that. Corrosion inhibitor additives must be used anytime there is more than one type of metal present in the system, especially when mixing aluminum and copper components to minimize the effects of galvanic corrosion.


Anodizing aluminum surfaces can help slow down the corrosion of the aluminum parts but it will not totally stop it. Aluminum naturally forms a protective oxide layer when exposed to air and the anodizing process forms an even thicker, harder oxide layer. The type of anodizing process used and the quality and uniformity of the resultant surface will affect how resistant it is to corrosion. Any scratches or breaks in the anodized surface will allow localized corrosion to set in.

Corrosion inhibitors can be added to water based coolants to help prevent corrosion. There are numerous corrosion inhibitors on the market, most of which have been designed for automotive cooling systems (Water-Wetter, Hy-Per Lube Super Coolant, Purple Ice, Zerex Racing Super Coolant, etc). However, a couple of products are being specifically marketed for PC water-cooling systems (Swiftech HydrX and InnovaProtect).

In addition to helping prevent the basic corrosion process, corrosion inhibitors and automotive antifreeze (which contains corrosion inhibitors) suspend corrosion products when they do form, keeping them in solution and preventing them from precipitating out on internal surfaces. These additives will slowly become depleted over time, requiring periodic replacement.

Water Additives

Water additives are used to help increase heat transfer, minimize corrosion, prevent organisms from growing in the water, and in some cases prevent the water from freezing. There are dozens of different products available with just about as many different formulations and features. For our purposes, water additives can be broken down into four main functional categories.


Surfactants (Surface Active Agents)

Surfactants (also known as wetting agents) decrease water’s natural surface tension. High surface tension causes water to be attracted to itself, which is why water beads-up on a slick surface. Surfactants are used in PC water-cooling systems to promote better heat transfer. They do this in several ways:

First, by reducing the surface tension, water can better wet the inside surfaces of waterblocks and radiators (get down into all the little cracks and crevices), which potentially leads to better heat transfer. Second, reducing the surface tension also helps release numerous tiny air bubbles that build up and become trapped on internal surfaces (microscopic air bubbles block heat flow). Third, as we mentioned earlier, reducing the surface tension can lower the viscosity of water slightly.

Household soap and detergent products (like Dawn liquid dishwashing detergent) are surfactants but should only be used in very small amounts if added to your PC’s coolant system (~2 drops per gallon). These products generally contain other additives (emulsifiers, sudsing agents, perfumes, etc.) that are not beneficial for PC water-cooling applications.

There are many different kinds of surfactants. Soaps fall into one class of surfactants (anionic) made from animal fats and vegetable oils. Detergents on the other hand include several types of surfactants (anionic and nonionic) made primarily from petrochemicals.

Surfactants are organic molecules, composed of two parts. On one end is a carboxylate group (alkylated carboxylic acid) and on the other end is a long straight hydrocarbon chain. The carboxylate end is attracted to water. This is the (hydrophilic – water-loving) end. The hydrocarbon chain end is repelled by water (hydrophobic – water-hating) but is attracted to other molecules and surfaces.

When a surfactant is added to water, it acts as a “bridge”, which allows the water to fully wet or spread out along a surface that might otherwise repel the water molecules. It is this same wetting ability of soaps and detergents that allows water to attach and suspend oil and grease for cleaning.

Water Wetter, Hy-Per Lube Super Coolant, Purple Ice, and HydrX are some of the more popular commercial additives that contain surfactants. Along with corrosion inhibitors, these products also produce an alkaline pH, which helps minimize corrosion and retards the growth of microorganisms.

Surfactants offer the potential for improving heat transfer but unless they are used properly and in the right amounts, they can sometimes do more harm than good.

Corrosion Inhibitors

Some type of corrosion inhibitor should always be used in a PC water-cooling system, especially when mixing dissimilar metals like aluminum and copper/brass. Automotive coolant system additives are one of the best sources for obtaining good corrosion inhibitors – just don’t use one that is designed to stop coolant leaks. Most all of the big name antifreeze manufacturers, and a few specializing in super coolants for race cars, market concentrated coolant additives containing corrosion inhibitors. As mentioned earlier, a couple of water-cooling companies also sell their own brand of corrosion inhibitors.


Here is a shortlist of coolant additives that have been specifically formulated to include corrosion inhibitors, which people have tried using in PC water-cooling systems (I’m sure there are others):

  • Valvoline (Zerex) Racing Super Coolant
  • Red Line Oil Water-Wetter Super Coolant
  • Hy-Per Lube Super Coolant
  • Purple Ice Radiator Super Coolant
  • Swiftech HydrX Extreme Duty Coolant
  • InnovaProtect Corrosion Protection and Heat Conductor
  • Prestone Super Anti-Rust
  • Silkolene Pro CCA Corrosion Control Additive
  • Automotive antifreeze (Prestone, Zerex, Dex-Cool, etc.)

If you don’t use enough corrosion inhibitors, you run the risk of corrosion occurring. If you use too much, you will degrade the overall cooling system performance. The greater the concentration of corrosion inhibitor additives, the more water’s excellent thermal properties will be diluted.

A great deal is known about corrosion and the many chemical substances that can be used to inhibit the corrosion process. There are dozens of specific corrosion inhibitors. Many are well understood while the exact mechanism of others remains a mystery. Scientists know they work but aren’t quite sure just how or why.

Corrosion inhibitors fall into many general classes like phosphates, silicates, and organic acids. Sodium molybdate is a common and very effective broad-spectrum corrosion inhibitor as is Tolytriazole. Sodium salts of molybdate, nitrate, nitrite, borate, benzoate, phosphate, silicate, etc. are used because they dissolve so well in water. Different chemicals will preferentially protect some metals better than others. Molybdate is particularly good for protecting copper and steel. Silicates are excellent for protecting aluminum but may be difficult to keep suspended in solution. Each commercial product I looked at typically uses a different formulation of corrosion inhibitors.

Corrosion inhibitors also contain pH buffers and stabilizers, which are designed to establish and maintain an alkaline solution, typically with a pH between 8 and 10. Acidic solutions are corrosive to metals, so maintaining an alkaline solution helps minimize corrosion. In systems that contain aluminum parts, the pH should ideally be maintained around 8. The protective aluminum oxide layer is susceptible to both acidic and strong alkaline solutions. It will start to deteriorate when the pH goes higher than 8.5.

For many years, the most common corrosion inhibitor used by many water-cooling enthusiasts has been automotive antifreeze. Quite a few of the water-cooling kits on the market today come with a small bottle of “antifreeze”. It’s readily available and, theoretically at least, should offer protection against corrosion.

By far the majority of corrosion inhibitor products on the market have been designed for automotive coolant systems. While PC water-coolant systems may be similar they are not the same. Some of the ingredients in automotive cooling system additives may not offer any benefits to a PC user and in some cases, they may even be harmful. Automotive coolant systems and the additives designed for them operate at much higher temperatures than a PC water-cooling system.

One of the first things we can look at to determine a particular product’s suitability for use in a PC water-cooling system is the resulting pH of the final coolant solution. The following table lists the pH of various products when mixed with distilled water at the manufacturer’s recommended concentration.


As you can see, all of the formulations produced an alkaline pH, which is good for minimizing corrosion. Three of the products produced a stronger alkaline solution (pH>10), which may prove detrimental to systems incorporating aluminum parts.

Many products list the active ingredients on the package. For the ones that don’t, a Material Safety Data Sheet (MSDS) can often provide insight on the specific chemicals being used. It’s not easy for mere mortals (like myself) to decipher what each of these ingredients is designed to do and what adverse effects if any they might cause in a PC water-cooling system. Luckily I have a few friends who are chemists… 🙂

One of the most popular products which contain corrosion inhibitors is Red Line Oil’s Water Wetter. According to Red Line Oil’s technical information, “Red Line Water-Wetter ® is designed to provide improved metal wetting and excellent corrosion inhibition… for all cooling system metals, including aluminum, cast iron, steel, copper, brass, and lead.” This all sounds good but let’s take a closer look at the active ingredients list (MSDS 03-10-99).

Red Line Oil Water-Wetter Super Coolant

  • Di-Isopropyl alcohol ether
  • Tri-Isopropyl alcohol di-ether
  • Sodium molybdate
  • Tolytriazole
  • Poly Siloxane Polymer

As we mentioned before, sodium molybdate and tolytriazole are both well-known and effective broad-spectrum corrosion inhibitors. The Siloxane (silicone) polymer is used as a surfactant to lower the surface tension of water and increase its surface wetting ability. So far, so good, but what do those two ethers bring to the mix?

Based on their structure, one chemist friend speculated they might be used to increase the boiling point and freezing point of water, but Red Line claims Water-Wetter doesn’t significantly do that. What is clear, though, is that they are both small molecules, strong organic solvents, which could have detrimental effects on some plastics. This coincides with reports I have received from people experiencing problems when using Water-Wetter in systems that have Plexiglas (acrylic) reservoirs – significant crack formation and splitting joints. The ethers may also be related to the slimy coating reported by some that builds-up on the inside surface of certain types of tubing.

I don’t mean to be picking on Water-Wetter – I use it only as an example to illustrate the point that most coolant additives are designed for automotive cooling systems and may not be quite as well suited for PC water-cooling applications.

Here is a list of the active ingredients for some of the other additives that claim to have corrosion inhibitors in their formulations. In general, most of these additives contain some combination of various pH buffers (sodium hydroxide, potassium hydroxide), corrosion inhibitors (sodium salts of molybdate, nitrite, borate, etc), and surfactants (Octylphenoxypolyethoxyethanol, Siloxane, etc):

Valvoline (Zerex) Racing Super Coolant

  • Not available (at least not that I could find)

Purple Ice Radiator Super Coolant

  • Proprietary

Hy-Per Lube Super Coolant

  • Sodium hydroxide
  • Sodium nitrite
  • Sodium tetraborate
  • Sodium molybdate
  • Sodium mercaptobenzothiazole
  • Octylphenoxypolyethoxyethanol

Swiftech HydrX Extreme Duty Coolant

  • Ethylene glycol
  • Ethylhexanoic acid
  • Potassium hydroxide
  • 4-Hydrobenzoic acid
  • Diethylene glycol

Prestone Super Anti-Rust

  • Petroleum distillates
  • Sodium Petroleum sulfonate

Silkolene Pro CCA Corrosion Control Additive

  • Refined mineral oil
  • Diethoxyethanol
  • Fatty alcohol ethoxylate
  • Sodium Sulphonate

Prestone Antifreeze/Coolant (green stuff)

  • Ethylene glycol
  • Diethylene glycol
  • Proprietary corrosion inhibitors

Prestone 5/150 Extended Life Antifreeze/Coolant (orange stuff)

  • Ethylene glycol
  • Diethylene glycol
  • Sodium 2-Ethyl Hexanoate
  • Sodium Neodecanoate

Biocides – Preventing Biological Growth

The growth of biological organisms, such as algae, fungus or bacteria, can rapidly degrade a system’s performance by fouling heat transfer surfaces and clogging narrow passageways. These microorganisms do not belong in a water-cooling system and can be easily prevented.

Two good ways to help prevent the growth of biological organisms are to disinfect all components thoroughly before assembly and eliminate potential food sources from the system. Tap water generally contains various microorganisms in small amounts. Once inside the system, they may flourish and grow. Using ozonated, distilled water to fill the system can reduce the initial charge of microorganisms. Boiling distilled water first (and other components that will not be damaged by the heat) to sterilize it is even more effective.

Some people add a small amount of liquid chlorine bleach to the coolant, but chlorine is corrosive, especially in higher concentrations. It is particularly corrosive to aluminum and stainless steel. I don’t recommend adding bleach to your system. If you do decide to use bleach, then only use it for short periods of time at a low concentration. After a quick rinse (~10 minutes) the system should be drained and repeatedly flushed until all traces of the chlorine bleach have been thoroughly removed.

Remember the before and after pictures back in the section on corrosion?


Obviously, I couldn’t wait 6 months to a year for this type of corrosion to develop while writing this article, so I used a corrosive solution that would produce the same effect in a shorter period of time. The corrosion illustrated in this picture was produced in just 2 hours using a 50% Clorox bleach and water solution – still want to put bleach in your system…?

Two additional methods that can be used to disinfectant a system before placing it into service are to run a 50% alcohol or Listerine water mix thru the system. Either Isopropyl (rubbing alcohol) or Methanol (wood alcohol) can be used. This should only be done for a short period of time (~1 hour) and then the system must be drained and refilled until the disinfectant has been removed. Listerine mouthwash is an effective over-the-counter antiseptic that kills most microorganisms.

One of the benefits of filling a system with distilled water is that there will be little organic material in the water for microorganisms to feed on. This can go a long way in minimizing their growth.

There are a number of commercial products that can be added to a PC water-cooling system to retard the growth of microorganisms. Additives like Water-Wetter, Purple Ice, Hy-Per Lube Super Coolant, and antifreeze do not contain biocides and won’t stop biological organisms from growing inside your system, but they can help deter the growth because they produce an alkaline pH.

Several products are available that can be added to the coolant to suppress the growth of microorganisms, including algae, fungus, and bacteria (both aerobic and non-aerobic). Asetek markets their own WaterChill Anti Algae Fluid for use in PC water-coolant systems. Swiftech’s HydrX also claims to “prohibits… formation of algae”. Another good deterrent is PolyScience Lab Algicide, which is used in laboratory water baths and is available through various lab supply houses like VWR and Cole-Parmer.


Numerous algaecides are on the market for treating swimming pools and hot tubs, but these products frequently contain chlorine or bromine and should be avoided because of their potential to cause corrosion. Methanol, even in relatively low concentrations, can be an effective general-purpose biocide, but by its very nature is also poisonous and even flammable when used at higher concentrations (>25%).

Copper sulfate and iodine crystals are two more effective biocides for the more adventuresome. Copper sulfate crystals dissolve readily in water and a little goes a long way. Iodine crystals don’t particularly dissolve in water (unless you have a water/alcohol mix) but just enough will go into solution to effectively kill the bugs.


The primary function of automotive antifreeze is to raise the boiling point and lower the freezing point of water. Glycol is commonly used for this purpose. There are basically four different kinds of glycol-based, automotive antifreeze on the market today:

  • Green – ethylene glycol base
  • Orange – propylene glycol base
  • Orange – ethylene glycol base (extended life)
  • Red – DexCool – ethylene glycol base (extended life)

Ethylene glycol (in all of its various formulations) is toxic to humans and animals. Pet-safe or environmentally friendly antifreeze is formulated with propylene glycol, which is much less toxic (also used as a food additive). DexCool is a new type of long life antifreeze that uses Organic Acid Technology (OAT) to form carboxylates, which last longer than traditional corrosion inhibitors. A lot of controversy surrounds this product – some car owners love it while others claim to be experiencing significant corrosion-related problems (particularly sports car and motorcycle owners).

As we saw earlier in Part I, glycol has a much higher viscosity (resistance to flow) than water. Adding antifreeze to your PC water-cooling system will increase the viscosity of the coolant and can reduce the overall flow rate thru the system. In addition, the thermal conductivity and specific heat of glycol is not as good as water. Combining these factors may result in a measurable drop in cooling performance.

Another potential disadvantage of using glycol-based antifreeze for corrosion protection in your PC water-cooling system is that it may not provide optimal protection due to a relatively low concentration. Antifreeze is designed to be mixed with water at a 50:50 mix. Most PC enthusiasts use a 15%~20% antifreeze to water mix. This means the concentration of corrosion inhibitors is much lower than what the manufacturer intended. Increasing the coolant mix to 50:50 would significantly decrease the coolant’s flow rate and ability to transfer/transport heat.

Most water-cooled PCs operate at ambient room temperatures, so there is usually no need to protect the water from freezing or to extend the boiling point. Systems that incorporate some form of active cooling (Peltier devices, refrigeration, etc.) may require freeze protection. The first thing that comes to most people’s mind is automotive antifreeze. But for all the reasons listed above, glycol-based antifreeze may not be the best choice.

Methanol (methyl alcohol) is an alternative choice, for freeze protection. It mixes well with water and does not decrease the overall system flow rate the way automotive antifreeze can. Methanol has a lower viscosity than water and is almost as good at conducting and absorbing heat as water. It can be purchased at some paint stores and home improvement centers. A mixture of 70% water and 30% methanol will provide freeze protection down to -30ºC.

On the downside, methanol is flammable (even a 30% mix with water will burn), poisonous and toxic. If you do use methanol, be careful not to get the liquid on your skin or breathe the vapors – both are neurotoxins. When using a methanol mix it is a good idea to use silicone tubing, because it is more resistant to methanol than Tygon (vinyl) tubing. Silicone tubing will also stay much more flexible at low temperatures than vinyl.

Reasons to use antifreeze:

  • Readily available
  • Provides basic corrosion inhibition

Reasons not to use antifreeze

  • Toxic to humans and animals
  • Higher viscosity than water (lower flow rates)
  • Thermal conductivity and specific heat not as good as water
  • Becomes even more viscous at lower temperatures
  • Diluted corrosion inhibitors may not provide optimum protection

For these reasons, it is generally better in my opinion to use a specially formulated super coolant additive instead of automotive antifreeze.


The water coolant in a PC requires regular maintenance to ensure optimal performance. In addition to periodically adding water, the system may need to be flushed and refilled as the chemical additives get used up over time. In some cases, if corrosion or microorganisms have begun to compromise the system’s cooling performance, a complete teardown may be required. In this section, we will discuss three basic types of maintenance.

  • Periodically adding water to top-off the system
  • Flush and fill to renew coolant additives
  • Teardown and cleaning of fouled surfaces

In a closed water-cooling system you might think that once the system was filled and all the air bled out, the water level should remain fairly constant over time. Unfortunately, this is frequently not the case. It is common for the water level to slowly drop in the fill tube or reservoir even in systems with zero leakage, requiring the addition of a little water every month or so to top-off the system. This occurs because most types of plastic tubing are slightly permeable to water vapor.

Although not technically correct, the simple explanation is that water “evaporates” thru the walls of the tubing. In reality, water vapor slowly passes thru the walls of the tubing. Silicone tubing is much more permeable to water vapor than vinyl tubing (Tygon, ClearFlex, etc). So, if you are using large diameter (greater surface area) silicone tubing, you may have to top-off your system with water more often than someone using smaller ID vinyl tubing.

In general, it is a good idea to drain and refill your PC water-cooling system at least once a year and, in some cases, every six months. Measuring the pH and observing the condition of tubing and waterblock internal surfaces can be a good indicator for when maintenance is required. The chemical properties of the water coolant will change over time as the additives get used up and the coolant becomes contaminated with corrosion byproducts.

Most people don’t have access to a laboratory pH meter, but inexpensive pH indicator strips can be purchased at some drug stores and swimming pool supply stores. When the pH drops below 7, or the water starts looking cloudy, or internal surfaces appear to be accumulating deposits – it’s time to clean the system and replace the coolant.


One popular cleaning method, pioneered by our friend Airspirit, is to flush the system with a mixture of 75% Pine-Sol and 25% Lysol. Drain and then refill your system with this mixture for really dirty systems or dilute the mixture up to 50:50 with water. Circulate this cleaning solution thru your system (preferably with the PC not running) for 10 minutes to 1 hour. Drain and flush the system until all traces of the cleaning solution are gone.


If you are trying to rid your system of an infestation of algae, fungi, or bacteria, another popular solution is to use a 50:50 mix of Listerine and water to kill off the germs. When you are finished flushing the system, drain and refill with distilled water and your favorite coolant additives.

Sometimes the only way to clean badly corroded parts is to disassemble the system and clean the individual components with a strong detergent and brush. Incorporating a two-piece waterblock that can be easily disassembled will facilitate cleaning the internal passages. If the tubing has become discolored or badly stained it may be preferable to just replace it with new pieces of tubing.

Remember, keep an eye on the system water level and watch for signs that the coolant is starting to become cloudy. Drain and refill your system with fresh coolant at least once a year.

Basic Coolant Mixtures

OK, we have talked a lot about some of the various coolant additives that can be used in a PC water-cooling system. Not all systems are alike, so what works best for one person may not be the best solution for someone else. Here are five examples of some popular coolant mixtures.

1. Distilled water (100% – no additives)


  • Excellent thermal properties


  • No corrosion inhibition
  • Various microorganisms may flourish

2. Distilled water and super coolant additive of your choice*


  • Good/Excellent thermal properties
  • Good corrosion resistance (depending on the effectiveness of additive)


  • May not provide any protection against microorganism growth

3. Distilled water, super coolant*, and biocide of your choice


  • Good/Excellent thermal properties
  • Good corrosion resistance (depending on the effectiveness of additive)
  • Good protection against microorganism growth (depending on the additive)


  • Added complexity and cost

4. Distilled water, 15% automotive antifreeze, super coolant*, and biocide of your choice


  • Fair/Good thermal properties
  • Good corrosion resistance (depending on the effectiveness of additive)
  • Good protection against microorganism growth (depending on the additive)
  • Sense of security – some people just feel better using this mix


  • Added complexity and cost
  • Higher viscosity – potentially lower flow rate
  • Toxic to pets and humans

5. Distilled water, 30% Methanol, super coolant of your choice*


  • Good thermal properties
  • Good corrosion resistance (depending on the effectiveness of additive)
  • Good protection against microorganism growth
  • Offers freeze protection down to -30ºC


  • Added complexity and cost
  • Toxic to pets and humans
  • Flammable

* (Valvoline Racing Super Coolant, Water-Wetter, Hy-Per Lube Super Coolant, Purple Ice, Swiftech HydrX, InnovaProtect, Silkolene Pro CCA, etc.)

Note: The excellent thermal properties of pure water may be decreased slightly by adding a small amount of super coolant or other additives but may be increased a tiny bit if the surface tension is reduced.


By now you have probably figured out that water has a unique combination of physical, thermal, and chemical properties that makes it ideal for use in PC water-cooling systems. However, to help minimize the negative effects of corrosion and prevent the growth of microorganisms, it is necessary to use coolant additives. And when it comes to all the various additives, I find there are numerous claims and opinions but very few facts.

I don’t know about you, but I feel like we are coming up short here. Yes, we have discussed water and many of the available additives that claim to make water better. But there appears to be very little hard information about which additives really do what they claim, especially when used in a PC water-cooling system.

Many different people that I have talked to have their own favorite recipe for a coolant mix. Water-Wetter and Purple Ice have probably been around the longest but Hy-Per Lube Super Coolant, Valvoline Racing Super Coolant, and Silkolene Pro CCA are currently favored by many experienced, water-cooled PC users. And let’s not forget Swiftech’s HydrX Extreme Duty Coolant or Innovatek’s InnovaProtect – these guys should certainly know what they are doing.

So how do you sort out the marketing hype and great claims from the facts and real-world performance? Does using one of the super coolants that claim to decrease the surface tension of water really produce measurable (keyword: measurable) results? I don’t have the answer to that question. In fact, I have a list of unanswered questions.

  1. How do the various additives affect overall cooling system performance?
  2. Which coolant additive (or combination of products) will provide the best corrosion protection for my PC water-cooling system?
  3. Which coolant additive is most effective at protecting against microorganism growth?
  4. Do any of the popular additives produce undesirable side effects when used in a PC water-cooling system (attack plastic parts and/or seals)?
  5. What is the best mix for my particular application?

In conclusion, I will say I am still a believer in using distilled water as the primary coolant, and I highly recommend using one of the above-mentioned coolant additives designed to protect against corrosion. I also plan to do some follow up testing to try and answer as many of the previous questions as possible. I am in the process of designing two tests/experiments to: (1) measure the overall heat transfer effectiveness of various coolant mixtures and (2) measure the ability of various additives to inhibit corrosion.

So, hopefully, I may have more information to share in the coming months. Thanks for reading and I hope you have found the information presented here interesting and useful.


Water has a unique combination of physical, thermal, and chemical properties that makes it ideal for use in PC water-cooling systems. However, to help minimize the negative effects of corrosion and prevent the growth of microorganisms, it is necessary to use coolant additives.

RoboTech (Lee Garbutt)


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