Red Engine Coolant Light On or Flashing

Red Engine Coolant Light On or Flashing

There are many dashboard warning lights on our vehicles; some more important than others. Red warning lights are the most urgent and some, such as the engine coolant light are even more urgent. To avoid potentially significant engine damage, it’s important that immediate action is taken if the red engine coolant warning light comes on.



Car engines are kept cool by use of water that constantly circulates around the hot engine components. This water (or ‘coolant’) consists of a mixture of antifreeze and water. The antifreeze solution itself is made up of Ethylene glycol or propylene glycol and distilled water.

When you pour 50 / 50 ration of antifreeze and water (or a pre-made solution) into your coolant reservoir, this mixture forms the coolant. The benefits of using coolant over plain water this is that it lowers the freezing point of the liquid. Normal water freezes at 0°C, engine coolant freezes at -35°C. This prevents the coolant from from freezing in most cold climates, therefore preventing engine damage.

Another benefit of antifreeze is that is raises the boiling point to help prevent the fluid from evaporating; it also means that the fluid will not boil at 100°C. Engine coolant does however begin to boil at around 106°C.

The engine coolant itself is kept cool due to passing through a radiator. When the vehicle is moving, air passes through the radiator fins that in turn, cools the coolant passing through the radiator. If the vehicle is stationary, a radiator cooling fan comes on, pushing air through the radiator.


What Does the Engine Coolant Light Mean?

The red engine coolant warning light means that the coolant fluid is too hot and that the engine is overheating. This could be due to or a combination of:

  • The engine is working too hard. This could be that the vehicle is towing or carrying a heavy load or that the vehicle is being driven fast with high engine speeds (RPM).
  • The outside temperature is high and the air passing through the radiator is warm and not cooling the system sufficiently.
  • The engine coolant fluid level is too low.
  • There’s a fault with the cooling system.

Red Engine Coolant Light On or Flashing

The engine coolant light may illuminate steady on or it may flash:

  • Illuminate steady: This means the engine coolant is too hot and the engine is overheating. An audible alert may also be heard depending on your vehicle.
  • Flashing: If the engine coolant light is flashing, it means there’s a fault with the cooling system. This could be a serious malfunction where coolant is no longer circulating the engine (faulty coolant pump) or it could be an electrical wiring (check connections) or sensor fault (temperature sensor or level sensor) causing the coolant warning light to flash.
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