There’ s plenty of confusion these days about the colour of heavy-duty coolants

It is often asked, does the colour indicate anything about the chemical make-up of the coolant, or is it just a brand to brand thing?
In this article, Cummins’ Head Chemist and coolant expert, Mike Hudson, seeks to clear the air about this confusion by answering some common questions.

What should we look for in a coolant?
First and foremost, choose a good quality coolant from a reputable brand and check that it has been tested to, and meets, a heavy-duty coolant standard.
One such internationally recognised standard is the ASTM D6210, and coolants that meet OEM standards are even better.
In terms of the coolant’s properties, it should have good heat transfer abilities and a higher boiling point and lower freezing point than water.
It should also prevent corrosion and erosion, resist foaming, be compatible with cooling system component materials, be compatible with hard water, resist sedimentation, and be chemically stable. Other considerations include the life of the coolant and its maintenance requirements.

Which colour coolant is the best?
The truth is the colour doesn’t mean anything.
In days gone by, the colour of coolant was determined by the types of chemicals used to prevent corrosion, meaning once upon a time, you could tell a lot about a coolant by its colour.
Older coolants that used Inorganic Additive Technology (IAT) were usually blue or green in colour. These types would normally have to be changed roughly every two years.
In the 2000s came Organic Acid Technology (OAT) coolants, whose chemical make-up offered better protection for cooling systems, and extended the life of the coolant.
These coolants were usually orange or red in colour and offered a five-year or 160,000km change interval.
There are also coolants which are a blend of IAT and OAT chemicals, and these were therefore named ‘hybrids’ (HAT) and were typically yellow or green; but not always.
Nowadays, we can’t rely on the colour to tell us about a coolant’s chemistry or performance.
Coolant marketers and OEMs have adopted their own tiered approach to differentiate their products, meaning the colour can no longer be used as a guideline to a coolant’s properties.
For example, PGPlus, a hybrid, lifetime coolant with 250,000km or 4,000 hours service intervals, is dark blue in colour.
And PGPlatinum, an organic, lifetime coolant which requires no service thanks to its superior additive package, is red in colour.
Is there a legal standard for coolant colours?
These days, there’s no legal standard for a coolant manufacturer to use a certain colour, so it’s not easy to know what chemicals are in the coolant just by seeing its colour.

How should coolant be maintained?
Every brand of coolant requires different levels of maintenance. Some coolants, such as Fleetguard’s OAT coolant and PG Platinum are lifetime. Meaning they do not need to be changed over the life of the engine. Others such as those containing nitrite used for cavitation protection, require additive top-ups, as the additives within them deplete over time. Fleetguard’s PGPlus is an example of this.
While some coolants are compatible with others, changing the chemical balance in the cooling system can be detrimental to its performance, so mixing different types of coolant is not recommended. All coolants, no matter the type, colour or brand, should be tested twice a year to ensure they are maintaining the correct chemical composition and concentration.

For more information about coolant and cooling system maintenance, visit