August 7, 2023

Does Coolant Matter?

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US Radiator 

Chemical Analysis- Does The Coolant Matter?

If you own a GM vehicle built after 1995, then you should know that you must use a specific type of anti-freeze in your cooling system called Dex-Cool. A radical departure from the classic green antifreeze, Dex-Cool is the orange stuff and was developed by GM as a long-life coolant. The intention of Dex-Cool was to eliminate water pump seal wear, as manufacturers were moving away from cast iron blocks in favor of aluminum. The results of Dex-Cool are fairly infamous, as the coolant itself turned out to interact poorly with plastic intake gaskets, causing major repair jobs.

The reality is that the gaskets were the problem, not the coolant, but this brings up an important question- what is the right coolant for your application, and does it matter what you mix it with? If you have a Dex-Cool engine and you refill it with the standard green stuff, you end up with a blob of jelly inside the cooling system because the two formulas are NOT compatible with each other. The situation is further complicated with “universal” coolant, which is generally green and looks similar to the original green stuff, but is not the same. You might have thought that all antifreeze is relatively similar, but it definitely is not.

There are all types of formulations for coolant as each manufacturer has their specific formulations, however in the United States, there are three main type of engine coolant: Original Green Inorganic Acid Technology (IAT), Organic Acid Technology or OAT-Based, and Hybrid OAT G-05 and G-11 coolants. You may ask “why does this matter to me, I have a 1970 Chevelle, the old green stuff is fine.” If you have the original engine, then sure, you would be right, but if you have LS swapped that Chevelle?

Classic Green IAT

Before 1995, anti-freeze was silicate-based ethylene glycol. This stuff has been in use since 1937, and was a simple affair. You mixed it 50/50 with water. As winter approached, you would check the mixture ratio with a squeeze-bulb tool called a refractometer. This miniature turkey-baster had 5 or 6 balls in it that floated based on the level of anti-freeze in the coolant. The main issue with IAT coolant is that it does not last all that long, 2-3 years was the limit, and it was a common practice to flush your cooling system every couple of years to make sure your engine and cooling system was protected. Over time, IAT coolant degrades rubber hoses and metal through galvanic or electrochemical corrosion. Essentially, there is an electrical charge inside the cooling system, and negative ions transfer from the metal or rubber to the coolant. You can use a sacrificial anode in your radiator to help reduce this corrosion, as the anode gives up ions freely so the iron block does not have to. The silicates used in IAT coolant are also abrasive, further damaging gaskets and seals.

IAT coolant uses ethylene glycol as the base, and then a mixture of silicates and phosphates are added to protect the copper brass, cast iron, and aluminum components in the cooling system. The additives used in IAT coolants leave a thin deposit on the metal inside the cooling system, a process referred to passivation. This only lasts a short time, hence the 2–3-year life span of IAT coolants. As more aluminum components were being used in engines, a problem arose with IAT coolant- it was discovered that the silicates in IAT coolant were causing scale build up inside the engine, and the phosphates were eating the rubber gaskets. IAT is the default coolant for all vehicles built prior to 1995, and should be used in all vehicles with copper-brass radiators.

 IAT coolant is highly toxic to animals. Because it smells sweet, animals and young kids may drink it, which is often fatal. NEVER leave spilled antifreeze on the ground, you must wash it away with fresh water.


Organic Acid coolants such as Dex-Cool were developed as a long-life antifreeze. In the early days, Dex-Cool was called a permanent antifreeze, but it only lasts about 5 years. OAT coolant uses a similar principle as IAT coolant for corrosion protection, but it is a slow acting process, giving it a longer lifespan. OAT coolants swap the silicates and phosphates for 2-EHA (2-ethylhexanoic acid), sebacate, and other organic acids. There are variations to the basic formula by manufacturer, some do not use 2-EHA, some add phosphates or other chemicals.  Another big change for OAT coolant is that the base switched to propylene glycol, which is not as toxic to animals and kids.

OAT coolant is the required formula for all 1995 and later GM vehicles, and most European and Asian vehicles built from 1995-2001. Unlike IAT coolants, OAT formulas do not cause corrosion from electrochemical corrosion. That said, OAT coolant is not the best option for copper-brass radiators, IAT is still the best option for older system.

Hybrid OAT

Most manufacturers now require HOAT coolants, with the major exception of GM, which still uses Dex-Cool. The hybrid in HOAT is the addition of silicate to the formula to provide fast-acting protection for aluminum. HOATs are the predominant coolant of choice for Ford, Chrysler and most European models. These coolants have a 5-year life span. The spec rating of G-05 and G-11 is used for HOAT coolants.

Universal Antifreeze

You have likely seen this on the shelves next to other antifreeze options. This is essentially an HOAT coolant formula which has swapped out the phosphates for nitrates.

So, what do you need for your vehicle? This really depends on the vehicle itself. The engine and radiator are the determining components in this decision. If your vehicle is as it came from the factory, then you need to choose the coolant that was recommended from the factory. These formulations are made for specific reason, and you want to use the right stuff. If you have a Subaru, you need Subaru Blue HOAT coolant. If you have a 2004 Chevy truck, Dex-Cool is the correct choice. You can use a universal coolant in a pinch, but the reality is that it is not as good as the specific coolant required for your vehicle. Engine swapped vehicles should use the recommended coolant for the engine, as the internal seals and gaskets used in that engine require specific attributes in the coolant.

Should you decided to change the coolant type, i.e., Dex-Cool to Classic Green IAT antifreeze, you ABSOLUTELY MUST flush the cooling system multiple times to ensure all the old Dex-Cool is out before refilling with IAT coolant. DO NOT forget to run the heater when flushing the radiator, the heater core doesn’t get fresh coolant when the heater is off, it is typically shut off with a valve.

Water Is Water Right? Wrong.

Back in old days, we would refill the coolant jugs with tap water and fill the radiator. This was wrong then, and it is even more wrong today. Certain additives in OAT and HOAT coolant do not react well with other minerals found in tap water. Hard water, which has a high concentration of magnesium and calcium, is really bad for your cooling system. Phosphates react poorly to hard water, creating scale that clogs the passages. Asian OEs use more phosphates in their HOAT coolants, so hard water is really bad for a Honda or Toyota.

The correct water for your cooling system is distilled water. There are multiple distillation processes that can be used, but the main point is to remove all the minerals and salts from the water. You can buy this water in gallon jugs, or make it at home using an RO system. RO, or reverse osmosis, makes two types of water- one is free of pretty much everything over that H2O, and the other output is highly concentrated with minerals and salts. Drinking distilled water does nothing for the human body, as we need the minerals, but it is perfect for the radiator in your car.

U.S. Radiator recommends skipping the mix altogether and instead use a pre-mixed 50/50 coolant of the correct type for your vehicle. This ensures that you not only have the right type of water and coolant, but also that it is the best ratio (50/50) for proper cooling, freeze protection, and corrosion resistance. Not to mention it is much easier to buy and store when you only need one jug.

“Why can’t I just use water?” is a common question, and the answer is you technically can, water will cool your engine, but it does not do anything to protect the metals and seals inside the engine, and it has no protection for freezing. Additionally, water has a fairly high surface tension, which makes it more difficult for plain water to transfer heat. There is a barrier between the water and the engine/radiator metals that limits thermal conductivity. The surface tension of water has a dynamic viscosity of 72 per centimeter, comparing this to a 50/50- mix of ethylene glycol and water, the dyn/cm factor drops to 56, making the coolant much more thermally conductive. You can feel this by dipping your fingers into plain water and rubbing them together, then do the same with 50/50 or pure antifreeze. Your fingers are much more slippery with antifreeze than they are with plain water, this is surface tension. You can see it when you spill water versus coolant, or other fluids. Standing water has a taller wall at the edge compared to antifreeze.

The lower the dyn/cm factor, the more thermally conductive coolant is. You can further decrease surface tension with special coolant additives called surfactants. These are available at any parts store, and they work quite well. However, this is not an opportunity to save on using antifreeze, you still NEED antifreeze in your engine’s cooling system for the lubrication and anti-corrosion properties, in addition to the whole not freezing when it gets cold outside thing.

As you can see, there is a lot more to antifreeze than color. You should always use the right coolant spec’d for your vehicle and engine, and always use distilled water or a pre-mixed antifreeze whenever possible. U.S. Radiator is ready to help you make the right choices on the radiator and heater core for your car, if you have any more questions as to the correct coolant or components you should use in your vehicle’s cooling system, give them a call at 800-421-5975 and their techs will get you on the path to a cool and reliable drive.