Coolant versus water in a car's cooling system
Many vehicle users do not see the need to use coolant in their vehicles simply because they put in water and their vehicle runs fine simply because they are unaware of the long term negative effect that it will have on their vehicle's cooling system and the engine itself.
Now, let's see how coolant performs when used and how water performs when used in the cooling system.
• Ordinary water - let's say either tap, well or borehole water. These water contain minerals that cause corrosion to engine block, piping and radiator core. Those minerals also cause scale formation. For better understanding, check your old home electric kettle, you will notice a brown layer under, that is scale! When water that contains these salts evaporates, it leaves behind the salts that forms scale.
Merit of the use of this as coolant is that the impurities help to raise the boiling point. It is not good to be used as coolant in the engine though because of the damage caused by those minerals. Scales and those mineral buildup can block passage in the radiator and other parts of the cooling system. It can also make the Thermostat to become stuck closed or stuck open or stock partially closed. This can have minor to severe effect on the engine.
• Demineralized water/distilled water - This does not contain thomse minerals that cause corrosion and scale. A cheap source is water that comes out of your air conditioner.
The merit of using this is, you won't have any scale formation with its use and it will boil at normal boiling temperature of pure water. It is bad for overheat protection because once the temperature reaches 100 degrees celcius, it begins to boil especially when the cooling system has lost pressure due to faulty radiator cap or leakage somewhere. Some vehicle's normal operating coolant temperature are as high as 105 degrees celcius.
• Coolant - The major content of coolant is mostly ethylene glycol. Its boiling point is high and its freezing point is low. This helps to give the engine high temperature protection, easy start and protection in freezing temperatures. Coolant also contains corrosion inhibitors that prevents corrosion and it is also used as lubricant for Thermostat and water pump.
As you can see, coolant does it all!
Note that water has better specific heat capacity than coolant hence, it conducts heat away from your engine better than coolant but coolant has higher boiling point which is desirable. There is a compromise which we must balance.
Common mixture ratio is 50% coolant and 50% demineralized water.
In a warm/hot climate like Nigeria, it is counter productive to have more coolant than water just because you want to raise boiling point to prevent overheat. Because of our relatively high ambient temperature, we need a medium for fast heat transfer. It is not good to exceed 70% water, 30% coolant in order not to loose protection of the engine.
You should dilute your coolant with demineralized water only. If you use common water like tap water, the result is a coolant that is already degraded.
Also, that there is coolant concentrate which will have to be diluted and there is pre-mixed which is mostly 50/50 mixture ratio of concentrated coolant and water. Always refer to the container of the coolant you buy for information.
Warning: Never mix coolant of different types or composition and color. If you have to change the coolant that you are using, you must do a thorough radiator flush.
Good quality coolants should also be used to get the best performance and longevity of the cooling system.
When the correct fluid is not properly used, it can shorten the lifespan of the cooling system, the engine and sometimes the transmission. How it can affect the transmission can be seen in this link.