https://chem-group.com/antifreeze-the-ultimate-guide/
Okay, I think this is a good article and worth reading all the way through to fully understand the issue. I've extracted what I think is the most relevant part of the article here;
THE DIFFERENT TYPES OF ANTIFREEZE
In terms of the major component, antifreeze mixes are available in the standard ethylene glycol-based form or the non-toxic propylene glycol-based version. But, that is not the main difference. The primary variation in antifreeze solutions is based on the anti-corrosive factors used in them. Up until the mid-nineties, ethylene glycol-based, bright green antifreeze mixes were the norm. However, newer vehicles and their advanced engine components raised the need for more effective antifreeze solutions that would offer greater protection. This led to red, green, blue, yellow and orange fluids. Every one of these is meant to address the specific requirements of various engines and their components.
So, you will find coolants and antifreeze solutions from nearly all major auto manufacturers that are designed to handle the anti-corrosive needs of the engines in their vehicles. When selecting the fluids for your car, it’s always a good idea to consult your owner’s manual first to see what your car’s manufacturer recommends.
WHY IS ANTIFREEZE DIFFERENT COLORS?
Both ethylene and propylene glycol are colorless fluids and the anti-corrosive compounds and other additives wouldn’t make much of a difference to their colorless form. However, given the variation in antifreeze solutions, manufacturers add colors to these mixes, so that it can be easy to differentiate one kind from another.
Basically, coolants come in 3 types:
1. Inorganic acid formula (IAT):
Used in all cars till the early nineties, this is your basic bright green coolant that is still poured into all older cars manufactured before the mid-nineties, including all domestic vehicles from Ford, GM and Chrysler. Made by adding phosphates and some amount of silicates to glycol, these low-silicate, conventional antifreeze solutions also have supplemental coolant additives (SCA) in them to protect the engine lining from corrosion. In fact, it’s the SCA that are the first components of the coolant to get exhausted. So,
these older green fluids need a change every 2 years or 25,000-30,000 miles.
2. Organic acid technology (OAT):
These coolants turned into the norm around the late-nineties and are still going strong in many newer cars all across the world. Although devoid of both phosphates and silicates, OAT coolants offer similar corrosion resistance as the green antifreeze mixes. But the anti-corrosive compounds in these solutions are slow-acting, which gives the product a
longer life span. Also, it is
specifically designed to offer anti-corrosive protection to the aluminum and nylon parts in newer model cars. Originally marketed as “permanent” or “long life” antifreeze,
OAT coolants, or Dex-cool as they are commonly known, have to be replaced every 3-5 years.
Another important difference is that unlike IAT coolants, OAT products use propylene glycol as the base, so they are less harmful for pets, kids and the environment in case of a spill or boil-over.
OAT antifreeze mixes are usually orange, yellow or red but also comes in other colors, such as blue, red and very dark green, depending on the variant and the manufacturer. These coolants are widely available and used in most GM cars and trucks manufactured after 1995 as well as in vehicles manufactured between 1996 and 2001 by Audi, Honda, Jaguar, Kia, Land Rover, Mazda, Nissan, Porsche, Saab, Toyota and VW.
3. Hybrid organic acid technology (HOAT):
As their name suggests, these coolants combine the best of IAT and OAT products to offer superior corrosion resistance for aluminum parts and rustproofing for iron components.
Typically, dyed yellow or orange, HOAT products are also available in a range of other hues such as pink, purple and blue. HOAT products are usually referred to as “global” and you will almost always find a label on the packaging which reads, “
Meets or exceeds G-05 specifications”.
These antifreeze mixes need to be changed every 5 years and are specified for most cars manufactured after 2002 by Audi, BMW, Chrysler, Ford, Mercedes, Saab, Volvo and VW.
As you may have noticed, color is certainly not a reliable indicator of the type of coolant that you are getting. The only thing that the different hues are good for is to prevent the inadvertent mixing of two types of products. So, always read the bottle’s description and match it with coolant specified in the owner’s manual of your vehicle. If the bottle description has you stumped, don’t take the risk of adding any odd coolant to the reservoir. Instead, take the trouble of checking with the local mechanic or repair shop. This may cost you a few bucks, but it will certainly be less expensive than a complete engine overhaul.
CAN YOU MIX ANTIFREEZE COLORS?
In short:
no, you cannot mix different types of antifreeze mixes. In fact, HOAT coolants are available in at least 3 variants (Silicated HOAT, Phosphated HOAT and Phosphate-free HOAT), and you
shouldn’t be mixing together even the variants, let alone the main classes. Mixing the green with the orange or orange with the blue/yellow, etc. will lead to a chemical reaction in the reservoir. This causes the formation of brown, gelatinous sludge in the reservoir and the radiator that can completely block the cooling system over time.