Rick's Free Auto Repair Advice

Coolant additives

What are the most common coolant additives?

Every engine and cooling system is unique, so you can’t use a universal all makes all models coolant in your engine without causing some type of damage. The coolant additives must match the metal used in the engine block, cylinder head, water pump casting and impeller and bearings, radiator, seals, plastic components, heater core and heater tubes. Car makers use Aluminum alloys, copper, copper alloys, magnesium, steel, plastic, rubber in their engine designs and the coolant chosen must be compatible with all those materials.

Ethylene glycol and polypropylene glycol make up about 95% of automotive coolants. Other glycols like 1,3-butylene glycol, hexylene glocol, diethylene glycol and glycerin can be used in small percentages. The rest is comprised of lubricants, surfactants and corrosion inhibitors.

Here are some of the most common coolant additives

Traditional green coolant contains silicates and triethanolamine phosphate, mercaptobenzothiazole sodium salt, sodium benzoate, sodium nitrate and borax. But silicate coolants have poor thermal stability, are unstable to pH and can gel when used with other corrosion inhibiting salts, reducing the cooling capacity of the liquid. Plus, silicates can precipitate out of solution, further reducing corrosion protection.

Thus they have a short life of under two years. Thus, car makers have gradually switched away from silicate based coolant to organic acid formulations.

In addition to glycol and carboxylates many organic acid coolants use the following coolant additives:

Sodium Benzoate is used and the primary corrosion additive in hybrid organic acid (HOAT) coolants and G-05
Benzotriazole (BZT) Protects against corrosion for brass and copper
Colligative agents raise or lower the boiling and freezing points of the coolant.
Denatonium is a bittering agent to protect wildlife in the event the coolant is spilled.
Molybdate prevent coolant cavitation near the cylinder liner.
Nitrate is used to prevent corrosion
Nitrite is used to prevent cavitation near the cylinder liner. Plasticizer – A substance that softens certain plastics, silicones, and nylons.
Sodium Hydroxide is used to help maintain pH balance.
Triazole / Thiazoles are used to prevent corrosion on brass and copper.
Tolyltriazole (TTZ) is also used to prevent corrosion on brass and copper.
2-EHA (2-ethylhexanoic acid) is a coolant corrosion additive that is also a plasticizer that can damage nylon components and silicone materials. Those materials are used in most modern engines.
sebacate and carboxylic acids
aliphatic mono- and dicarboxylic acids

For more information on IAT, OAT, HOAT coolants and how they differ, see this post

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