ALS Tribology eSource
March 22, 2012

Routine Engine Coolant Analysis
By David Doyle, CLS, OMA I & II, Vice President & Operations Manager and
Ed Eckert, CLS, OMA

Coolant testing provides an important tool in maintaining the health and operating reliability of commercial and industrial engines, yet many times this benefit is overlooked. Properly performing cooling systems are an integral part of a drivetrain power system. It is commonly reported by industry and service suppliers that 40% of engine failures are cooling system related. Whether this number is true or not, it is recognized that poor performing cooling systems do contribute greatly to engine reliability problems.

Routine coolant testing detects contaminants such as total dissolved solids (TDS), as well as iron, copper, and aluminum due to corrosion of the metal surfaces. Coolants themselves degrade over a period of time to form glycolic and formic acids.

Basic testing will report glycol concentration, as well as TDS, freeze point, boiling point, pH, and nitrite (SCA) level in the mixture. Additional testing will report the level of the corrosion inhibitor additive package which prevents deterioration of metal surfaces. Silicates, borates, nitrates, and phosphates are commonly used in various proportions in conventional coolants as corrosion inhibitors. Additional testing can also monitor the breakdown of the glycol, by determining the level of glycolate acids in the coolant.

Extended Life Coolants (ELCs) use organic acid technology for inhibitors (OAT). The organic acids in ELC formulations have been neutralized to form highly effective corrosion inhibitors. There are a variety of organic acids used in ELCs for these inhibitors. Coolants manufacturers will use different combinations of organic acids depending on their proprietary formulations.  Different corrosion inhibitors in the coolant formulations, whether conventional or ELC, are intended to protect specific types of metal surfaces such as, iron, brass, copper, aluminum, and soldered components.

Testing will also indicate whether there has been improper mixing of conventional and/or extended life coolants by monitoring the level of the inhibitors used in conventional coolants, and the cumulative Organic Acid Technology (OAT) inhibitors levels used in Extended Life Coolants (ELCs). Some engine manufactures require specific inhibitors or do not permit other types, such as Phosphate free coolants.  Routine analysis of the coolants will monitor formulation requirements.

Cavitation can be a major problem in engine cooling systems, especially on water pump impellers, and cylinder sleeves. Cavitation is a big concern with coolants during extended service. Fluctuation of pressure will create vapor bubbles which collapse under high pressure. Over time, cavities will form, which will ultimately lead to cylinder sleeve failure. Cavitation is very destructive by causing pitting on metal surfaces. Inhibitors that reduce the vapor pressure and surface tension of the coolant need to be monitored to ensure that they are maintained at an effective concentration. Inhibitors such as nitrites, phosphates, sodium, and molybdate additives are used to prevent cavitation.

Another problem that crops up from time to time, which testing can help detect, is when nitrites react aggressively with aluminum in the presence of organic acids used in ELCs. The reaction creates ammonia which raises the pH and creates a caustic situation that erodes radiators and other cooling system components.

Proper monitoring of the coolant in an engine circulating system can prevent pitting of cylinder sleeves (leading to shortened engine life), premature circulating pump failures and frequent radiator repairs.




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