What is the right coolant to use in our older cars?


Coolant (Antifreeze) manufacturers have quietly moved over to new Organic Acid Technology (OAT) from the old Inorganic Acid Technology (IAT). The new formulas are great for modern cars, but in most cases they are totally unsuitable for anything made before about 1990. Luckily some manufacturers are still making the older IAT formula ethylene glycol based coolant, but it is becoming harder to find. As a general rule, the IAT coolant is blue (in the UK ) and the newer OAT coolant is pink (in the UK), but may be other colours in other countries.

OAT inhibited coolant is known to cause leak problems especially in engines that use wet liners, such as most liquid cooled classic Citroens. The major fault with the inhibitor is that it attacks, amongst other things, silicone compounds. The most commonly used base compound for gasket sealants is silicon. It also attacks lead based products like solder that holds our radiators and heaters together.

I once had a 1964 ID19 in the workshop for a service and when I removed the spark plugs, I found that all 4 had pink coloured centre electrodes. Upon investigating, I found that the cooling system had been filled with pink OAT coolant and this had attacked the inlet manifold gasket causing some coolant to be mixed with the air and fuel entering the engine. It went through and out the exhaust along with the combustion gasses, but the dye stayed behind on the spark plugs to tell the story!

For the past few years we have been using pre-mixed IAT Ethylene Glycol coolant in our workshop to avoid getting the lime scale and other contaminants from tap water into the cooling system and reducing it’s efficiency. But lately, this is getting harder to find, especially in reasonable sized quantities. Not only that, but I was concerned about the toxic nature of ethylene glycol. As little as 30ml of ethylene glycol can be fatal in adults and 4ml can kill a cat. It has a sweet taste, so a child or animal finding some either spilt or in a bottle is not put off drinking it by the taste. It also damages paint if spilt on it and as little as 1% ethylene glycol in your engine oil causes rapid main bearing failure, resulting in a ruined engine.

I knew there had to be a better alternative, a coolant which will not attack components in our older cars, poison or children and pets and is more environmentally friendly.

The solution is to use Propylene Glycol based coolant, and from March 19th 2012 we no longer have toxic ethylene glycol coolant in our workshop, we now use exclusively non-toxic, environmentally friendly, long lasting, pre-mixed Propylene Glycol coolant.

Propylene Glycol coolant for all cars, including classics.Environmentally friendly, non-toxic, long lasting, highly efficient anti freeze coolant for all cars, including classics.Environmentally friendly, non-toxic, long lasting, highly efficient anti freeze coolant for all cars, including classics.

Environmentally friendly, non-toxic, long lasting, highly efficient anti freeze coolant for all cars, including classics.

  • Propylene glycol is hazy yellow in colour, is non-toxic, will not damage paint, is bio-degradable, and can be mixed with drinking water.
  • Propylene glycol has a bitter taste that makes it less attractive to curious animals and children.
  • Propylene glycol does not persist in the environment. It is readily consumed by microorganisms. In an activated sludge treatment plant operating at 65 deg F, PG is fully degraded within 24 hours.
  • Propylene glycol does not break down into corrosive elements, and can be used for many years retaining excellent aluminium protection, and prevention of lime scaling around the copper tubes in the blocks.
  • Tests have shown that aluminium corrosion was lower for PG based antifreeze than for an EG version.
  • In laboratory and engine dynamometer studies, PG antifreeze has performed better than similar products containing EG with regard to cast iron cavitation corrosion.
  • Heat Transfer efficiency of propylene glycol is superior to ethylene glycol that cannot carry as much heat. More fluid must be circulated to transfer the same amount of energy. Pump volume is increased.
  • Fuel economy, and other key performance characteristics were the same for both PG and EG coolants.

The Propylene Glycol coolant we now use is Classic Coolant from AAA Solutions Ltd which will last the lifetime of your engine, provided it is regularly checked and the protection level maintained. This makes it very cost effective and there really is no reason for anyone to still use the toxic ethylene glycol coolant.

UPDATE JULY 2020: The above coolant is no longer available and we are now using a pre mixed propylene glycol coolant from Penrite. Search propylene on our website to find it.

3 Comments on “What is the right coolant to use in our older cars?”

  1. John Nicolai says:

    Can you find this coolant in the US?

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