Can using tap water instead of coolant cause engine overheating in my Swift?

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Can using tap water instead of coolant cause engine overheating in my Swift?

I’ve been topping up my 2013 Swift’s radiator with regular tap water during summer. Recently, it’s been overheating more often. Could this be due to rust o r scale buildup from using untreated water instead of proper coolant?

Gari Specialist asked on 03 May 2025 12:59:51 pm

1 Answer

54 views |

Gari Master - on 08 May 2025 16:26:22 pm

Yes, using tap water instead of coolant can absolutely cause engine overheating in your Suzuki Swift, especially under the demanding driving and climate conditions in Pakistan.

Here’s why:

Why Tap Water Alone Causes Overheating:
Lower Boiling Point:

Tap water boils at 100°C, whereas coolant a mix of antifreeze and distilled water has a higher boiling point of 105–120°C.

In hot Pakistani summers, o r while stuck in traffic, your Swift’s engine can reach o r exceed 100°C. Without coolant, water may boil and evaporate, leading to overheating.

No Thermal Buffer:

Coolant contains ethylene glycol o r propylene glycol, which helps dissipate heat more effectively.

Tap water alone does not provide sufficient thermal protection, especially when the engine is under load e.g., AC use, uphill driving.

Mineral Buildup:

Tap water in many areas of Pakistan is hard, containing minerals like calcium and magnesium.

Over time, these minerals form scale deposits inside the radiator, reducing cooling efficiency and causing localized overheating called hot spots.

Corrosion and Rust:

Coolant includes anti-corrosion additives to protect the radiator, water pump, and engine.

Tap water promotes internal rusting, leading to clogging and damaged components—ultimately causing overheating.
What You Should Do:
Drain and flush the radiator if you’ve been using plain o r tap water.

Refill with a 50:50 mix of coolant and distilled water, o r use pre-mixed coolant.

Stick to reputable brands like ZIC, Caltex, Toyota Long Life, o r Guard Coolant.

Check coolant levels monthly and never top up with tap water—use distilled water if coolant isn’t available temporarily.