Mining industry proves to be the harshest environment for mining vehicles. Engine overheating serves as one of the common causes of machine breakdown. This leads to an increase in breakdown time which depletes production and man-hours, which are very critical in mining operations. Typical reasons include: Low or no coolant or wrong ratio of antifreeze and water topped up in coolant tank, clogged radiator due to ingress of dust and dirt, water pump failure thereby affecting coolant circulation, thermostat failure thereby not allowing the coolant to flow at a particular temperature set by the manufacturer, coolant leak via hoses or fittings or low oil levels.
Coolant proves to be one of the important elements of the cooling system and will be discussed in detail further in the article. Let’s first refresh our memory on the vehicle’s cooling system.
Combustion cycle in automotive engines generates a huge amount of heat along with the power to convert the chemical energy of fuel into mechanical energy. A certain amount of heat gets removed via exhaust gases, but the leftover is removed via the cooling system of a vehicle. The main components of a vehicle’s coolant system include:
Coolant reservoir/tank: Used to store coolant. It consists of a cap which helps in regulating the pressure of the engine cooling system.
Water pump: Draws coolant from the lower tank and circulates it around the engine block, cylinder head.
Radiator: It serves as the most vital component of the cooling system. It consists of aluminium fins which act as a heat exchanger and cools down hot coolant received from the upper tank.
Cooling fan: The fan blows air through the radiator fins thereby dissipating heat of coolant.
Thermostat: It helps in maintaining the engine operating temperature.
Rubber hoses: These are hoses in which coolant travels.
Coolant: A liquid used to transfer engine heat.
A coolant is a liquid which acts as a heat transfer liquid used to reduce or regulate the temperature of the engine. Coolant is also referred to as antifreeze mixture. This mixture consists of antifreeze and softened water mixed in 50/50 ratio. Depending upon the vehicle’s application and environment, the ratio can be modified, like for vehicles running in extremely cold environments, a higher amount of antifreeze is used in comparison to water.
Antifreeze lowers the freezing point of pure water from 0°C to -37°C and raises the boiling temperature from 100°C to 106°C. Most coolant brands use Ethylene Glycol (EG) as antifreeze, although some brands use Propylene Glycol (PG).
Both are slightly viscous liquids having a high boiling temperature of 193°C and 188°C. The main difference between the two is the level of toxicity, Ethylene Glycol (EG) being more toxic and should be handled with extreme care.
Next comes softened water. To understand the significance of softened water we have to first understand the problem with tap water and distilled water. Tap water shouldn’t be mixed with antifreeze as it is rich in minerals. Regular use of tap water results in mineral build-up also referred to as scaling, inside the radiator thereby resulting in a drop in cooling efficiency. On the other hand, distilled water has no minerals and is better than tap water in terms of scaling. But the process of water distillation makes the water chemically unstable which on regular use can harm metal parts inside the engine. Softened water utilizes water softening techniques which leaves chemically stable water at the end of the process which is also free from minerals. It proves to be the best fit coolant mixture.
Then comes additive packages that are added to the coolant to enhance anti-corrosive and other desirable properties.
Last comes dyes which are added to impart colour for identification.
Coolant can be classified in two ways
Based on availability:
Premixed: Coolant which is available in mix form containing equal ratios of antifreeze and softened water and is ready to use.
Straight: Coolant which is available in sole antifreeze form and softened water has to be added before using it.
Based on coolant technology:
Inorganic Acid Technology: Generally used in old cars. Is green and purple and contain corrosion inhibitors like borate, nitrate, nitrite, phosphate, molybdate and silicate. The additives used gets quickly consumed thereby exposing the system to corrosion. Lifespan is typically up to 2 years or 80,000 km.
Organic acid technology: Offers silicate-free protection, thereby minimizing scale build-up and providing superior cooling performance than IAT technology. Lifespan is typically up to 5 years or 250,000 km. Is available in red and orange colour.
Hybrid organic acid technology: As the name suggests, it’s based on IAT and OAT technology and contains a combination of inorganic salts and some fully neutralized organic acids. Is available in red and yellow colour and has a lifespan of up to 5 years or 250,000 km.
It is always advisable to replace coolant as per the recommended time given in the vehicle’s manual. Certain solutions are available in the market which can be used to flush rust and other contaminants out of the system but should be used only when recommended in the vehicle’s service manual.
Often in underground mining operations to combat overheating, in absence of coolant, water is topped up which proves to be a quick fix but can be very deteriorating for engine components. In this event, immediate coolant maintenance is required as soon as the machine is available on the surface.
Currently, there are several coolant test kits and in-lab analysis services available in the market to examine coolant. Some of them are mentioned below:
One of the primary inspections that can be done is to examine coolant tank cap for the presence of any rust on spring. Rusting of spring indicates a higher amount of water than antifreeze in coolant mixture. This also means the inception of corrosion inside the cooling system.
Safety first: Extreme caution should be taken before removing the coolant tank cap, allow the engine to cool down and wear proper personal protective equipment’s. Release the coolant tank cap slowly so that pressure inside can be prevented from erupting.
Coolant test kits/equipment’s
Coolant test strips: These are disposable test strips used to measure pH level and glycol percentage. The colour of strip changes after coming in contact with coolant. The kit includes a chart which depicts coolant condition values for every colour and can be used for comparison.
Hydrometers: It is used to measure the specific gravity of antifreeze. The apparatus contains small disks in a plastic tube which floats when coolant is drawn inside the tube via suction bulb. The performance of antifreeze is determined by the number of discs floating. The test is temperature sensitive and values may vary depending upon coolant temperature at the time of the test.
Refractometer: A more accurate tool than hydrometer which determines coolant concentration by measuring the amount of light that gets bent as it travels through the engine coolant. Refractometers also have a similar downside as hydrometer of temperature sensitivity.
Lab analysis of coolant
Various ASTM tests are available to examine in-service coolant for wear metals, additives, pH, freezing point, boiling point and alkalinity. Vacuum pump method is generally used to draw coolant sample.
Coolant leak detection
Tracer dyes: These are fluorescent dyes which gets circulated inside the cooling system and when the system is scanned using a night lamp, the dye pinpoints the exact location of coolant leak.