Why you should avoid using water as a coolant

What you need to know:

You could use water as a coolant in an emergency. However, doing so is not recommended since water will not work well beyond its freezing and boiling points, which could cause expensive engine damage

Frequently, motorists use water as coolant. While the radiator will need water because it is the same that serves the wipers, the tank next to it (radiator) does not need water but coolant. Robin Byaruhanga of Deutsche Auto Services Uganda, says the tank that takes in the coolant is an opaque overflow tank made of plastic.

“It is opaque to allow one see inside and ensure the coolant is at safe levels. There are also markings on the side to help one know how high or low the coolant levels are,” he explains.

What is coolant?

Byaruhanga says coolant also known as antifreeze, is a coloured liquid that is mixed with water to help regulate a car engine temperature during extreme temperatures.

“It is used to regulate the engine temperature to an operating one while ignoring the external/outside temperature. In other words, even when the surrounding temperatures soar high, the engine is maintained at the manufacturer’s set temperature,” he says.

According to mandmservicecenter.com, coolant is a 50/50 mixture that is meant to increase the range at which water will boil or freeze. That way, rather than freeze at zero degrees Celsius and boil at 100, this water/coolant mixture’s freezing point is -37 degrees Celsius while the boiling point is 106 degrees Celsius

Dangers of using water

There is a big difference between using proper coolant and water for the car engine. Karl Magomu, a mechanic, says while water helps to keep your engine cool, it does not work nearly as well as coolant does.

“Water boils faster and at a lower temperature than coolant. As such, it gives false information to the engine control unit which leads to high fuel mileage/consumption,” he shares.

Therefore, while a car owner may think they are saving by using water, they are ultimately paying more for fuel. Byaruhanga adds that since water boils faster, it will evaporate, which increases internal pressure.  “That will trigger the relief valve to vent off. Ultimately, you will have to keep checking the radiator for right level of coolant,” he shares.

Additionally, the extreme temperatures can make the cylinder head warp or the gasket head blow. It can also result in other severe forms of engine damage since the water evaporates, hence quickly running out of coolant, which can cause the engine to overheat.

In countries that experience winter, Byaruhanga says, engine blocks will crack due to extreme cold weather if one has used water instead of coolant. Magomu points out that coolant protects some engine parts such as the flanges from corrosion, which makes most parts rust and others soft.  “Coolant prevents rust. However, when one is using water in its place, there will be constant leaks and blockages,” Byaruhanga shares, adding that running water rather than coolant will damage the coolant pump faster.

Best practices

Every car brand does lab tests for their engine parts and then manufactures the ideal coolant for them.

“This way, they avoid damage and also maintain the right operating temperatures in the engine. It is, therefore, best you use what the car manufacturer recommended for your car. Every car has a specific grade and type and most are written in the user’s manual or somewhere in the engine bay. For instance, for most European cars, it is written on the coolant reservoir tank,” Byaruhanga says.

While there are coolant brands, he adds, these do not really matter as long as one uses what the car manufacturer recommends.

Selling points

Magomu says coolant can be purchased from any shop that sells car parts.

“However, the easier places would be petrol stations, car parts stores, and hypermarkets. You can also talk to your mechanic to get you the right type,” he advises.

While the prices are not specific, because they are determined by the brand and type, they range from Shs15,000 to Shs50,000 per litre.


There is no engine built to run water as coolant, except the ones built before coolant was invented in 1926/28. To avoid unnecessary costs and disruptions, it would be best that you use what the manufacturer recommends.

Coolant can run for one year without the need to top up if the system is working fine. In that case, it will need changing or flushing out after 30,000km or two years for it to be flushed out or changed.


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