Using the wrong antifreeze just isn’t cool

Hey there, time traveller!
This article was published 24/08/2007 (6659 days ago), so information in it may no longer be current.

GREEN, blue, orange, red, yellow and even pink. If these were car colours it wouldn’t be any problem, but these are colours that you may find in the cooling system of your vehicle. If you want to add antifreeze, how do you know what type to use? Way back when, life was simple and antifreeze was green. Any other colour — usually rusty brown indicated either contamination with another fluid or rust in the system. Flush the coolant and install new antifreeze. Most brands were green and compatibility wasn’t an issue.

Today, there are mainly three different types of antifreeze used in passenger vehicles. Traditional green antifreeze, the original universal formula that everybody used until the introduction of today is extended-life coolants has proven to provide protection in vehicles from all areas of the world. The short-lived nature of the corrosion inhibitors however means this type of coolant should be changed every two to three years or 50,000 kilometres, although some brands now claim longer service intervals.

OAT-based antifreeze (Organic Acid Technology) includes ingredients such as sebacate, 2-ethylhexanoic acid (2-EHA) and other organic acids, but no silicates or phosphates (except for phosphates in Toyota’s extended-life coolant). OAT-based coolants are usually dyed a different colour to distinguish them from traditional green antifreeze. GM OAT-based Dex-Cool is orange. Volkswagen/Audi uses pink dye but Honda extended-life OAT coolant is dyed dark green. OAT corrosion inhibitors are slower acting but last much longer, so service life is typically five years. OAT corrosion inhibitors provide excellent long-term protection for aluminum and cast iron, but may not protect copper/brass radiators and heater cores in older cooling systems. There are different combinations of additives in OAT coolants from different manufacturers. While some may work fine in older cars, unless you can verify that they are fine for copper or brass, you should probably stick with green coolant in your older vehicles.

The third type of antifreeze is a Hybrid OAT coolant. This formulation also uses organic acids but not 2-EHA and add some silicate for quick-acting protection for aluminum parts. Hybrid OAT coolants can be found in many newer Ford, Chrysler and European vehicles.

To add to the colour confusion, some European and Korean coolants are dyed blue. Mercedes uses a yellow dye in its coolant. Toyota’s extended life coolant is dyed red. Saturn and some European makers also use green dye for their extended life coolants.

So what do you buy if you need to add antifreeze? You can’t go by the colour of the dye in the coolant because two coolants with similar colours may have different chemistry, and two coolants with different colours may have similar chemistry. There are several brands of aftermarket antifreeze that claim to be compatible with any type of coolant, regardless of colour, however, auto manufacturers recommend filling with only the same type as originally came in the vehicle. This means a trip to the dealership for antifreeze, unless you are flushing the whole cooling system.

Then you can fill with any type of antifreeze as long as it is designed to protect the components in your cooling system. Older vehicles had brass radiators and heater cores. Most vehicles now have aluminum components, so check the antifreeze label to see if it suitable for older vehicles. Mixing two different types of antifreeze may create incompatibility with the additives packages and reduce system corrosion protection although the freezing and boiling points of the coolant will still be good as long as it is mixed at the correct ratio of antifreeze to water. If you mix traditional antifreeze with long life antifreeze, the coolant life is shortened to that of the traditional antifreeze.

When you buy antifreeze, read the label carefully. Some containers come pre-mixed, ready to add to the cooling system. Other containers are concentrated and require a 50/50 dilution with water for maximum freezing protection, although some brands use a 60/40 mixture of antifreeze to water ratio. What may appear to be an economical purchase could actually be more expensive because you need to buy more antifreeze to get the same protection.

There is much more to the chemistry used in antifreeze, such as whether it is ethylene glycol or propylene based antifreeze. The more we get into the specifics of each type of coolant, the more confusing the whole issue becomes. That’s why it is important to always use the coolant chemistry recommended in the vehicle owners’ manual. With a little advanced knowledge, you can ask the right questions before you or someone else tops up your cooling system with antifreeze.

Jim Kerr is an experienced mechanic, instructor of automotive technology and member of the Automobile Journalists’ Association of Canada. You can e-mail questions to Jim at the address below.

kerr.jim@sasktel.net