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Introduction – Coolant

Since the invention of the internal combustion engine, it has been essential that the engine is cooled to prevent it ceasing up. This has typically been done either by forcing air cooling across fins on the periphery of the engine block or with the use of water circulating within a jacket around key parts of the engine.

An engine liquid coolant system is a set of various parts that allow liquid coolant to flow through passages in the engine. The system comprises a series of channels cast into the engine block and cylinder head, surrounding the combustion chambers with circulating water or other coolant to carry away excessive heat. The coolant is usually a mixture of water and antifreeze, which helps to stop the water in the system from freezing under normal cold weather conditions and it also increases its boiling point. A pump, driven by a pulley and belt from the crankshaft, drives hot coolant out of the engine to the radiator, where a fan forces ambient air across it cooling the water before it is returned to the engine block. Most modern engines have a sealed cooling system so they shouldn’t need topping up, unless, of course, they’ve sprung a leak in some way. Engine coolant levels should be regularly checked (see manufacturers guide) so any problems can be spotted early.


What is Engine Coolant and What Does It Do?

For many years the coolant used in most engines was a mix of local drinking water and antifreeze (of various types).  Locally sourced tap waters contain minerals in various quantities depending on sources geographical location. Over time these minerals form deposits at various locations within the engine leading to corrosion of the cooling channels, less effective cooling of the engine, hardening of flexible coolant pipework higher risk of pump cavitation again leading to reduced cooling efficiency and potential over heating of the engine.

There are several types of coolant used in diesel generators today which include ethylene glycol, propylene glycol, water, hybrid coolant, and coolant additives.

The aim of these additives is to:

  • Remove excess heat from the engine
  • Prevent the coolant freezing
  • Provide corrosion and wear protection


Coolant versus Antifreeze

  • Engine coolant: A liquid that regulates the temperature of the cooling system (Mixture of glycol and water)
  • Antifreeze: An additive which lowers the freezing point of water-based liquids (Glycol)


Coolant Differentiators

  • A specific blend of inhibitors used
  • Quality of glycol used…some use recycled gycol
  • Quality of water used: water with minerals can cause
    • Drop out of some inhibitors
    • Plugging cooling systems
    • Poor heat transfer

Coolant composition

  • Water – low cost and provides good cost effective heat transfer
  • Glycol – improves boiling and freezing point
  • Additives – protect against corrosion and cavitation
  • Dye – colours coolant

Composition of Coolant / Water Requirements

The component parts of the engine coolant each play a critical part in how the product performs and the impact its performance has on efficiency of the engine itself

  • Water quality is critical
    • Poor water quality is a leading cause of cooling system issues
  • Hard water causes drop-out of some additives and plugging systems, leading to poor heat transfer
  • Calcium, Magnesium, Sulphate, & Chloride are the elements to pay attention to
  • Some engine manufacturers have water performance requirements such as
    • Calcium, Magnesium <170ppm in summation
    • Chloride <40ppm
    • Sulphate <100ppm
  • Ideally coolants are made with highly purified water i.e. Distilled, deionized, reverse osmosis



There are two types of glycols in the market, ethylene and propylene

Glycol is a commodity item and there is little variation in quality unless recycled is used. Glycol is included in coolants for the following purposes:

  • Glycol lowers the freezing point of water
  • Glycol increases the boiling point of water


Composition of Coolant -Additives / Inhibitors

The additives included within engine coolant provide protection against corrosion, cavitation and a build-up of scale. These specially selected additives are the main point of differentiation between coolants. There are three types of Additives or Inhibitor Syrups:-

  • Inorganic Salts (IS)
  • Organic Acids
  • Hybrid Organic Acids (Combination of 1 & 2)

All of these additive types can be used with Ethylene Glycol or Propylene Glycol


Inorganic Salt (IS) Quick Facts:

  • Used in traditional green coolants
  • Most OEM’s have moved away from this technology
  • Sacrificial; form a protective layer, coating everything in the cooling system


Organic Acid Technology (OAT) Quick Facts:

  • Variety of acid types
  • Passivates the surface of the cooling system
  • Not all organic acids are created equal, some are more effective than others
  • Many OEMs have moved to this technology


Hybrid Organic Acid Technology (HOAT) Quick Facts:

  • Mix of both IS and OAT additive types
  • Contains inorganic salts for fastest acting protection
  • Currently popular for diesel and gaseous powered applications


Inhibitor Market Trends

  • There is a trend now to use what are known as NAP or NAPS free coolants. The component elements of these products are
  • N = Nitrite
  • A = Amine
  • P = Phosphate
  • S = Silicate
  • The NAPS free products tend to be more compatible with other coolants available on the market.
  • Many OAT and HOAT technologies are NAPS free but this should be checked.

Know your coolant composition

The final addition to a coolant product is a dye which does not provide any performance improvement but is there to provide an indication of the type of coolant being used. In general industry follows this convention:

  • Conventional coolant = Green
  • Light Duty OAT/HOAT = Yellow
  • Heavy Duty OAT/HOAT = Red
    • Other colours chosen by OEM to be unique = Blue, Orange, Pink, Purple, etc.


Kohler Genuine Coolant

Kohler’s Genuine Coolant is a Hybrid Organic Acid Technology (HOAT) product which is a mix of both inorganic salt and organic acid technologies. Kohler’s formulation contains silicates and may also be referred to as an Si-OAT(SilicatedOrganic Acid Technology) which provide the long life of OAT additives with the fast-acting benefit of Inorganic salt additives.

Kohler’s Genuine Coolant is a -26ºblend

Kohler’s genuine coolant products have been formulated based on years of experience and many tens of thousands of engine running hours. It uses the very highest quality elements which include:

  • Highly purified water
  • High quality ethylene glycol Kohler’s coolant formulation does not contain any recycled glycols
  • High Quality Additives:



Kohler’s coolant is a low silicate formulation or NAP free. Kohler chose a low silicate concentration to provide the following benefits:

  • Long / extended service intervals of OAT coolants… Extended life of up to 5 years or 8000 hours
  • Inorganic salts provide fastest initial protection
  • Does not require Supplemental Coolant Additives (SCAs) to maintain silicate corrosion protection to metal components, the organic acids provide protection after initial silicate protection
  • The low concentration of silicates will not lead to silicate gelling or build-up
  • Inhibits and protects all metals and
  • Alleviates pitting
  • Reduces cavitation and any erosion caused by cavitation
  • Biodegradable, with a low toxicity hence is environmentally friendly?
  • Full engine coolant system in one convenience package


A typical engine maintenance regime would include a coolant system flush followed by coolant replacement every three years. The extended life of the Kohler coolant product means: –

  • Coolant system flush and coolant replacement only required every five years
  • Reduced maintenance cost
  • Reduced engine down time


G R Halliday

Business Consultant

WB Power Services Ltd