What to do if Coolant Light Comes on?

What to do if Coolant Light Comes on?

Failing to react to the coolant warning light, whether constantly on or flashing may result in significant damage to the engine. In some instances, the engine may be irreparable. If the coolant warning light comes on, you should do the following:


  1. Immediately turn on the heater at maximum temperature and maximum fan speed. This will transfer some heat away from the engine.
  2. While taking traffic conditions into account, safely pull off the road and switch off the engine.
  3. At this point, the coolant fluid is going to be extremely hot. If there is steam coming from under the bonnet / hood, wait until it subsides before opening it.
  4. If no steam is emitting from your engine compartment, open the bonnet and visually check the coolant reservoir tank level. Coolant levels should fall between the MIN. and MAX. markers located on the side of the tank.
  5. DO NOT open the coolant reservoir cap until you have allowed sufficient time for it to cool. This may take 15 to 30 minutes depending on the size of your engine. The coolant system is pressurised and opening too soon may cause hot liquid and steam to gush out causing scolding. Even after allowing time to cool, it’s advisable to use a cloth draped over the cap and very slowly opening it to allow the pressure to release first.
  6. Top up with engine coolant if necessary and ensure the coolant warning light has gone out before continuing your journey.
  7. Check under the engine compartment for visible signs of a leak. If coolant is leaking, it’s highly advisable to not continue your journey and arrange recovery.

Can You use Water Instead of Coolant?

Yes you can use normal water instead of coolant in an emergency. However, the correct use of engine coolant is essential as it raises the boiling point of the liquid, lowers the freezing point and provides corrosion inhibitors. If you have used normal tap or bottled water in your coolant tank, have the system drained and replaced with coolant as soon as possible.

Why Is the Coolant Light On?

The engine coolant warning light comes on due to:

  • Driving style / consistently high engine speeds.
  • The engine coolant level is too low.
  • Coolant leak.
  • Water pump has malfunctioned.
  • Loose / broken serpentine belt / fan belt.
  • Saturated / clogged catalytic converter.



How Long can I Drive with Low Coolant?

Whether or not it’s safe to drive with low coolant depends on the circumstances. It would be advisable to pull off the road, switch off the engine and check to see if there’s any coolant remaining in the expansion tank. If there’s coolant in the tank, it’s at or just under the minimum mark and there’s no signs of a leak, you should be good to carry on as normal. Ensure you top up with coolant before your next journey.

If there’s no remaining coolant in the expansion tank, then it’s difficult to assess how much remains in the system and the chances are, with that much loss of coolant, there could be a leak. Under these circumstances, it would not be advisable to continue your journey unless you can top it up.

What to do if Coolant is Boiling?

If engine coolant starts to boil, steam will emit from the engine. If your coolant is boiling, engine damage may have already occurred, but acting quickly can be the difference between a usable engine and one that has suffered catastrophic damage and that is irreparable. If the engine coolant is boiling, pull off the road as quickly and safely as possible and immediately switch off the engine. Check coolant levels after allowing sufficient time for the engine to cool.

What to do if Coolant is Empty?

If the coolant tank is empty, it’s usually an indication of a leak. Continuing to run the engine with an empty coolant tank means the engine has no means of cooling and will rapidly overheat and malfunction. The following typically occurs:

  • Water pump malfunction.
  • Blown head gasket.
  • Cylinder and piston damage.
  • Warping of the cylinder head.

In these circumstances, the cost of rebuilding the engine may equal or exceed the cost of a replacement (used) engine. If coolant levels are empty or extremely low, air can circulate and get trapped in the cooling system. The result of this is the engine may overheat even after adding coolant. If the coolant tank is empty, it’s advisable to have the cause (possibly a leak) rectified, have the system correctly sealed, filled with coolant and any trapped air released.


Coolant Light Comes on When Car Starts

If the coolant light comes on when you start the car and goes out when you start driving, it usually means that the coolant level is a little low. When the engine coolant is cold, the coolant level sensor triggers the warning light. As the coolant heats up with the engine, it expands raising the level. Check coolant levels when the engine is completely cold and top up if necessary. This is not applicable if the coolant warning light is blue.

Blue Coolant Light

On some cars (usually Japanese), a blue coolant light illuminates to inform you that the engine coolant is cold and is not yet up to optimal operating temperatures. This simply means that you should avoid high engine loads until the blue coolant light goes out. It’s not necessary to wait until the blue coolant light goes out before driving the vehicle.

Coolant Light Comes On and Off

If the coolant light randomly comes on then goes off and the coolant level is acceptable, it’s likely that you have a faulty coolant level sensor. It may also be a faulty thermostat that regulates temperature levels.

What to do if Coolant is Freezes?

If winter has arrived and you’re using normal water in your car’s cooling system, chances are it will freeze. A symptom of a frozen cooling system is when you start the engine, there will be a squealing sound. This is due to the fan belt trying to spin the frozen solid water pump pulley. Due to the engine no longer receiving a constant flow of coolant, the engine may also begin to overheat. The only real option here is to allow the water inside the engine to thaw and the time this takes depends on the temperature. If the water is only partially frozen, you may be lucky and receive no damage. If the water has frozen through, due to the expansion of ice, it’s likely that you will have caused damage to the engine and various other components such as the radiator.

What to do if Coolant is Brown?

Brown engine coolant is usually a sign of rust. This occurs when normal water has been used rather than proper engine coolant. Engine coolant contains properties that prevent corrosion. If the fluid is quite thick and sludge like, another possibility is due to a mixture of different coolant types. There are different types of engine coolant and there will be a specific type recommended for your vehicle by the manufacturer. Different coolant types should not be mixed as they can react and cause the fluid to thicken. Whatever the reason, it’s advisable to have the cooling system flushed and cleaned.

More about Engine Coolant
Link Engine coolant light on / flashing
Link What to do if engine coolant light comes on