Understanding Different Types of Antifreeze

In the Antifreeze world today, one thing is for certain when trying to decipher what can work in your car – confusion abounds! In the older days of cars (by older, referring to anything pre-1990) antifreeze was green, you mixed it with tap water – 50/50, and you called it a day. Today, times have changed, with antifreeze every color of the rainbow and people insisting certain things you can – and cannot do.

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Types of Antifreeze

The first thing to understand is the different basis for certain types of antifreeze.

Traditional antifreeze (the old green stuff) is known as IAT antifreeze, which refers to Inorganic Acid Technology. It was fortified with silicates and phosphates, which were used primarily to keep corrosion down within the system. This was especially important when the primary item that coolant was protecting from was rust in cast iron in engine blocks, heads, and other engine components in the cooling system made from iron.

During the 1980’s – as more and more vehicles began to use aluminum parts and rubber seals in the system, more problems began to occur. For example, silicates caused massive amounts of scale in the system when in contact with aluminum, further causing cooling issues. Phosphates on the other hand, over time, dried and corroded anything rubber – like water pump seals. The life of IAT antifreeze breaks down heavily around 36,000 miles in the system, causing massive corrosive issues once the coolant begins to break down. It breaks down so bad, that it can even begin to conduct electricity through electrolysis and begin eating your system from the inside! Because of this, European and Japanese manufacturers began working on OAT, or Organic Acid Technology Antifreeze.

OAT antifreeze has a replacement interval of 150,000 miles or generally 5-7 years, and depending on the make, is either silicate free, phosphate free, or both. OAT antifreeze began in the American market with GM’s introduction to Dexcool Orange in 1994. Other manufacturers began tweaking and making OAT coolant better through technology – providing coolant that was either safer for the environment, had even better anti-corrosion capability, or even had change intervals as long as 10 years.

These coolants, either Subaru Blue, Toyota Red, or VW / Audi G12, which is Purple, are the reasons why sticking with the factory-spec’d coolant intended for the vehicle is highly recommended over going with an “all makes” coolant – it is far superior. These colors added by the manufacturer are more-or-less markers to tell you first and foremost, what is in your system currently, and second, an easy identifier to tell you what the right coolant is, and that you are adding the right stuff to the system. For instance, if the reservoir of your VW you see purple, and you’re adding a VW specific purple coolant, it makes it very easy to see that everything is good! All coolant of this variety is either silicate free, phosphate free, or both, and is designed specifically to meet the needs of that particular manufacturers’ testing.

What Are “All Makes” Coolants?

So what exactly are the “all makes” coolants? They are HOAT – Hybrid Organic Acid Technology. This is an Antifreeze where manufacturers use Nitrates to literally make a “tweener” antifreeze – that’s something in between IAT and OAT – meaning, it’s a jack of all trades, and a master of none. It works, and is a great alternative in a pinch, but there are better methods and options for the customer if their vehicle requires a specific antifreeze – like the Pentosin and Peak manufacturer-specific antifreezes on the market. Mixing traditional IAT (green) antifreeze with an OAT antifreeze can also cause a world of problems. In the late 90’s, Dexcool, GM’s new OAT Antifreeze suffered this wrath and for a while, garnered a horrible reputation because unknowing customers were mixing traditional green IAT antifreeze into their Dexcool systems, eventually creating a brown nasty sludge over time that many consumers faulted Dexcool for. Dexcool was not the problem.

Besides the type of antifreeze you decide to use, there are some very important points that are worth educating yourself on:

All antifreeze breaks down – whether it’s 36,000 miles with IAT, or 5, 7, 10 years or 150,000 miles – it must be changed and flushed at some point. If you are unsure whether it’s been flushed, it probably hasn’t – it’s a good idea to change.

Your heater core is the most neglected item in the flush. Heater cores fail from one thing – corrosion from within. During the summer months, your heater circuit is shut off from regular circulation in the car’s cooling system, and the bottom of the heater core becomes a sediment pool and the source of corrosion. Your heater core can be flushed directly by simply running your hose-flush through the heater hose and into the heater core. Many customers who do this report nasty, brown sludge coming out of the heater core, or sometimes, complete blockage from debris and sediment. Remember, affording a $50.00 flush isn’t bad. A $1,200.00 heater core job really hurts.

The only universal part of coolant is water – different coolant types should never be mixed. Some studies show that mixing IAT and OAT antifreeze actually caused more corrosion than water alone (remember the GM Dexcool issue above!). If you are unsure what antifreeze is in your system, the antifreeze is brown, an off-color from what is recommended, or what has been put in is an HOAT “all makes” antifreeze, the best option is to plan a flush as soon as possible.

Lastly, we need to discuss water, because it’s actually not the easy part! Distilled water is the best option when mixing. While customers love 50/50 antifreeze for top-off, for flush and fills, buying concentrated and mixing yourself is the most cost-effective way to go. Using tap water, which is full of silicates, minerals, and other corrosion-causing garbage, is the worst possible thing to do over time. Distilled water or Reverse Osmosis water cost $1.00 a gallon, and is pure water. While tap water may seem like an easy thing, avoid the temptation to use it. You can get the parts you need at your local AutoZone Store. If the job is too big for you, seek out one of our Preferred Shops to help you do the job.

Advice, how-to guides, and car care information featured on and AutoZone Advice & How-To’s are presented as helpful resources for general maintenance and automotive repairs from a general perspective only and should be used at your own risk. Information is accurate and true to the best of AutoZone’s knowledge, however, there may be omissions, errors or mistakes.

Be sure to consult your owner’s manual, a repair guide, an AutoZoner at a store near you, or a licensed, professional mechanic for vehicle-specific repair information. Refer to the service manual for specific diagnostic, repair and tool information for your particular vehicle. Always chock your wheels prior to lifting a vehicle. Always disconnect the negative battery cable before servicing an electrical application on the vehicle to protect its electrical circuits in the event that a wire is accidentally pierced or grounded. Use caution when working with automotive batteries. Sulfuric acid is caustic and can burn clothing and skin or cause blindness. Always wear gloves and safety glasses and other personal protection equipment, and work in a well-ventilated area. Should electrolyte get on your body or clothing, neutralize it immediately with a solution of baking soda and water. Do not wear ties or loose clothing when working on your vehicle.

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