Engine Coolant analysis – protect your engine when hot or cold

Engines convert only ~1/3 of the energy from fuel combustion into kinetic energy to move the crankshaft. This leaves over 2/3 of the energy as heat through the exhaust (1/3) and conduction through the engine block (1/3). Water is not the ideal coolant because it boils at a reasonably low temperature compared to the engine temperatures and freezes during winter in all but the warmest of climates. Engine coolants (anti-freeze) have a high boiling point and low freezing point using mixtures of glycol (ethylene or propylene), corrosion inhibitor additives and deionised water.
Ethylene glycol is the most extensively used glycol, but with progressively strict environmental / toxicity requirements and the increased use of biofuels in which propylene glycol is a waste product of manufacture, propylene glycol is now becoming popular. These formulation types are built to specific OEM requirements. Mixing coolant types is not recommended and can compromise coolant condition, reducing its effective life and protecting properties on the engine.

With the emissions regulations tightening, there is a tendency for engines to run hotter; a potential problem when typical aluminium alloys are difficult to protect in high heat with traditional coolant technologies. This has led to Extended Life Coolants (ELCs) to combat the greater demands on the cooling systems. These deliver much of the functionality of Supplementary Coolant Additives (SCAs) to achieve by using Organic Acid Technology (OATs) additives. This increasing dependence on reliable coolant technology for efficient and reliable engine performance has also increased the demand for engine coolant sampling to compliment the already well established lube oil sampling programmes of customers.

Start your coolant programme by sending an unused reference sample.

Before starting your coolant analysis programme, owing to the vast differences in coolant additive technologies on the market, it is advisable to send references of all coolants in use with their product datasheets before starting your programme so that a baseline reference can be obtained of which additive package is in use. Furthermore confirm with the laboratory whether the filters in use contain SCA additives so that correct recommendations can be made if additives are low, and can identify the source of problems e.g if. a pre-charged SCA filter has been accidently used with an ELC coolant.

Appearance, Clarity and Colour – Part of the engine coolant assessment begins at sampling with a brief visual inspection of the sample, which can be performed both by the laboratory and sampler. Appearance photographs can also be included on your Lubetrend report on request – click contact us at lubetrend.com for details.

Diagnostic Significance: The visual inspection looks for clear and bright coolant with no hazy or opaque appearance, which could suggest degraded / contaminated or incompatible coolant mixes. Engine coolants tend to be brightly coloured and should stay roughly the same colour as when first taken from the coolant container. A change in colour or browning in colour can suggest mixing of coolants, coolant degradation or contamination.

Appearance – Visible Debris – This isthe most common abnormal flag for engine coolants and so deemed its own section. The samples as part of the appearance inspection identify any deposits, debris or sediment in the sample.

Diagnostic Significance: The sample should preferably have no visible debris, but in practice this is not always possible even with excellent sampling procedures. It is important to distinguish between 1 or 2 insignificant dirt particles that occurred at sampling compared to the more serious sediment caused by additive drop out, rust, hard water soap deposits, etc. These deposits can suggest corrosion to oil cooler/radiator or water pumps or poor coolant mixing with tap water. Further, evidence of emulsification or a visible floating hydrocarbon layer suggests evidence of fuel or oil, which could indicate either poor sampling, poor coolant storage or a leak between oil and coolant systems. This can be confirmed by sampling oil for the presence of coolant contamination and pressure checking the coolant system.

Glycol Concentration & Freeze Point – Glycol concentration is one of the major factors for both maintaining a sufficiently low freeze point for cold winter climate as well as maintaining a high boiling point to ensure the fluid does not boil at operating temperatures.

Diagnostic significance: This level is unlikely to change due to a machinery fault and a too high or too low concentration is typically owing to operator error in topping up with either too high or low concentrated mix. Hence, why it is often recommended to top-up with pre-mixed coolant where available to safeguard this does not occur. The protection of the engine is maintained by having an optimum level of glycol for operation, but too much glycol can also lead to a decreased effectiveness in maintaining a low freeze point (see chart to right), which shows that for an example product above 60% glycol, the effectiveness starts to decrease. This is because water is required for efficient heat transfer to the coolant mix.

Typical Diagnostic Limits: 

Glycol – Low typically <40% and high >60%. However, a common manufacturer recommendation is to have at least 33% and some pre-mix coolant solutions with OEM approval are supplied at 20%. Therefore, it is best to consult your engine manufacturer or coolant supplier if they have any bespoke recommendations for your equipment.

Freeze Point – This depends on environmental conditions and is usually country specific. E.g. artic areas would require a lower freezing point than desert areas.

pH – This indicates the acidity (low pH) or alkalinity (high pH) tendency of the coolant.

Diagnostic significance: Too high or too low a pH can lead to metal corrosion in the coolant system. The usual reasons for a pH change are either coolant degradation or contamination with another product.

Causes of low pH include:

  • Air leaks
  • Combustion gas leaks (usually ph <7)
  • Improper coolant levels maintained in system
  • Low additives if mixing own SCAs (conventional coolant)
  • Electrical grounding issues (note changes in odour)

Causes of high pH include:

  • High additives if mixing own SCAs or mixing ELC coolant with SCAs; possibly by  SCA filter
  • Mixed coolants
  • Contamination with an alkali water based product

Typical Diagnostic Limits: 

Conventional coolants – Min 8.5 to Max 11.0

Extended life coolants – Min 7.5 to Max 9.5

Total Dissolved Solids (TDS) – This is a measure of the total dissolved cations, anions and organic compounds dissolved within the sample.

Diagnostic significance: A high value can indicate either contamination with the system such as hard water components, or over-dosing with SCA additives. A typical maximum value is <20000 ppm. At high values the clarity of the product will start to become hazy too.

Possible Actions to take when high include confirming if using deionised water and check if SCA filter is overdosing system.

Reserve Alkalinity – This measures the ability of a coolant to neutralise acids e.g. glycol breakdown products or via exhaust gas leaks into the system. The rate of deterioration can indicate the severity of a fault and also be used to predict a coolant change.

Diagnostic significance: Too low a value and the protection of the coolant system may be impaired.

Conductivity – This is the total measure of electrically charged particles (anions and cations) within the system. The higher the number, the higher the contamination within the system because the particles make it easier for the fluid to conduct electricity.

Diagnostic significance: A high value can indicate either contamination with the system, e.g. hard water or over-dosing with SCA additives.

Total Hardness – This is the sum of total calcium and magnesium hardness within the system.

Diagnostic significance: Any hardness is an indicator of potential poor water quality and deionised water should always be used when producing coolant mixes. A typical limit maximum would be 85ppm.

Ion Chromatography (IC) – This looks at the negatively charged particles not normally detected by traditional coolant testing methods. This detects contaminants, inhibitors and degradation acids caused by air leaks, hot spots, electrolysis and general overheating.

Glycol breakdown products

Glycol based coolants have to endure extreme temperatures within the engine and dissipate this heat through the radiator. Eventually, the glycol breaks down and degrades to different chemical compounds. There are several stages to this process. An example with ethylene glycol is shown below, but the process is similar with other glycol types. The process includes

Elemental Analysis (ICP) – This is a commonly used tool for determining elements in samples by heating the sample in a plasma flame and measuring the wavelengths of light emitted as they cool (further details available in our YouTube Video minutes 16 to 18).

Corrosion Types Definitions – To understand the types of corrosion listed in the corrosion metals, some terms require defining.

  • Whole System or Uniform Corrosion – A general corrosion of the entire surface metal which is not localised. Typically caused by drops in pH, poor coolant or water condition. Variations on this are sometimes called crevice corrosion, which occur in specific parts of the system with little or blocked flow e.g. under gasket, clamps, washers or in small cracks where the coolant forms an acidic microenvironment.
  • Pitting – Often termed porous liner, or cavitation. Caused by the formation and collapse of air bubbles (termed condensation nuclei). Usually caused by vibration of system causing vapour bubbles to implode, low coolant pressure, slight imperfections on the surface wall either at manufacturing or by deposition of hard-water soaps / coolant additives.
  • Wear – sometimes called erosion, in which abrasive particles in the coolant wear the coolant system walls.
  • Galvanic corrosion – This is where two metals in contact with the coolant forms an electrical cell leading to breakdown of one of these metals either due to a manufacturing fault or poor coolant choice.
  • Electrolysis – This usually occurs when an electrical system fault ends up being grounded by the cooling system, which is essentially an electrolyte and can leads to severe breakdown of coolant systems, particularly in aluminium based systems.

SCA Number – This is used when calculating the amount of supplementary coolant additives (Nitrite and Molybdate) within the system so that there is sufficient protection against liner pitting and scaling.

Typical Diagnostic Limits. Values <1.2 require additional charge of SCA additive if system is suitable for their use, whilst values >3.0 units per gallon suggest that the system is over-charged with SCA additive.

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