Antique Cars and Antifreeze

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So what’s cooling your antique car ...IAT or OAT type antifreeze?  What’s the difference, you ask?  To be honest, I didn’t realize there were different types of antifreeze compounds.  I just shopped for brands and price.  I figure it’s all the same stuff just different colors.  Well, there IS a difference and it DOES matter to all of us that have water cooled antiques.

We need to avoid using OAT type antifreeze.  Even though it is designed for a longer service life, we shouldn’t use it.  It includes an inhibitor that attacks silicone compounds that are frequently used in gasket sealants.  In addition, this formula also goes after lead based products like solder and babbit (used in early bearings), some yellow metals that may be in cam bearings and radiators, and conventional gasket and seal type packing materials.   Our old rides may contain some, or all, of these materials so using OAT formula antifreeze could result in an expensive headache down the road.  We need to be looking for IAT type antifreeze to protect and preserve our investments.

Rather than spending hours and hours doing research to go into more detail, I think my time is better spent using the internet to gather useful information written by folks much more knowledgeable than I am.  If you want to know more, check out the links below.  Thanks to John Baldwin for suggesting this topic.

Hemmings antifreeze article Popular Mechanics

Motor Age Article Another Motor Age Article

AACA Forum on the subject AACA Forum on Extended life antifreeze

IAT type antifreeze products to seek out

OAT formulated antifreeze brands to avoid

HOAT formulated antifreeze   brands to avoid

IAT or Inorganic Acid Technology


Ethylene glycol  based, lasts for 3 years or
36K miles, color = green

OAT or Organic Acid Technology

Propylene glycol based good for 3-5 years, color = orange or yellow  (less poisonous than IAT)

HOAT or Hybrid Organic Acid Technology

color = yellow  or, possibly,  green, pink, blue, red or orange


Peak, Peak HD Sierra, Zerex Original


Anything labeled “extended life” or “extended service”, Dex-Cool (GM brand),  Zerex G-05, Zerex Asian Vehicle,  Most Prestone products

Note, watch for this table to grow as more brands are listed.  Your input is encouraged.

Your chapter would like to see more articles on automobile related topics.  Feel free to submit your articles in any state from concept to polished and ready to publish.  I’ll do the rest.