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A horror for any driver: you’re on the road and suddenly one of the indicator lights on the dashboard lights up – engine overheating. Want to quickly drive the few miles home? Better not. Stop immediately and let your car cool down.

There’s obviously a problem with the cooling system and the engine is threatening to overheat.

Find out here how you can recognize a loss of cooling water in good time and what the causes can be.

The most important things:

  • When fuel is burned in an internal combustion engine, a lot of heat is generated that has to be dissipated by the engine’s cooling system.
  • This involves the use of so-called antifreeze, which circulates in the engine’s cooling water circuit and carries the heat away from the engine to the radiator, where it is released into the ambient air.
  • Various defects can cause this cooling water to be lost and, as a result, the engine can no longer be cooled properly. The engine can then overheat, resulting in engine damage.

This guide will tell you how to recognize a loss of cooling water, what to do then and what the possible causes are!

Caution: The expansion tank for the coolant is under pressure. Only open it when the engine is cold. Otherwise, there is a risk of severe scalding.

Symptoms/signs of a loss of cooling water

  • The coolant level in the expansion tank below MIN.
  • Puddle of cooling water under the car or in the engine compartment.
  • Engine temperature too high (observe the display in the instrument cluster – if necessary also note in the on-board computer).
  • White smoke from the exhaust, because cooling water is evaporating in the engine
  • Engine oil is diluted because cooling water has entered the oil circuit.

What should be done in the event of a loss of antifreeze?

  • Since a loss of coolant can lead to engine damage, it must always be taken seriously. For this reason, a workshop should be visited as soon as possible, even at the first suspicion.
  • A diagnosis must then be made first. The first step should be to pressurize the cooling system. This will determine whether there is a leak in the cooling system at all. If this is the case, the exact cause must be sought further.
  • Before going to the workshop, check the coolant level in the expansion tank.
  • If the level in the expansion tank is below the MIN mark, you should have the car towed to the workshop as a precaution.

Find out more: How to check coolant level?

How much antifreeze loss is normal?

Provided that the car’s engine is behaving well, no leakages or damages are there so far, and the engine isn’t old enough.

A coolant drop of 0.25″ every four months is normal as per car manufacturers and experts.

In a car, coolant loss is normal and might have several factors contributing to it, especially the engine and radiator’s issues.

As the engine becomes old, the evaporation rate increases and leads to a loss of 0.25″ in every four months, i.e., 1″ every year.

It’s advisable to keep refilling the coolant container with ample liquid regularly. Plus, a clean radiator can also minimize this coolant loss.

Possible causes of a loss of coolant

how-much-antifreeze-loss-is-normalRadiator leaking/defective

The radiator (also called a water cooler) is located at the front of the car. It cools down the temperature of the circulating cooling water through the airflow and with the help of an additional radiator fan.

If it leaks, e.g. due to corrosion or a stone chip, cooling water can be lost.

A leaking radiator must be replaced with a new part. The use of radiator sealants is generally not recommended.

Coolant hose leaking/defective

Within the cooling water circuit, the cooling water circulates through so-called cooling water hoses (also known as cooling water pipes or radiator hoses).

Leaks can occur due to oxidation on pipes and hose clamps or incorrect installation. Porous or damaged rubber seals can also cause corresponding problems.

As a result, there is a steady or even sudden loss of cooling water at the leaking point. The affected coolant hose must either be replaced in the workshop or reassembled correctly (e.g. in the case of a defective hose clamp).

In addition, the lost coolant must be topped up in accordance with the manufacturer’s specifications.

Water pump/coolant pump defective

The water pump ensures that the antifreeze circulates in the engine’s cooling water circuit. Wear inside the pump can cause leaks, resulting in a loss of cooling water. If the fluid level drops too much, this can also cause engine damage.

A defective water pump must be replaced as quickly as possible. The effort and cost of replacement vary depending on whether the water pump is mechanically or electrically driven.

Cylinder head/cylinder head gasket defective

The cylinder head sits directly on the engine block (crankcase) and seals it off at the top. In addition to the valve control system, the cylinder head in gasoline engines contains, for example, spark plugs and various intake and exhaust ports.

A cylinder head gasket seals the cylinder head against the engine block. If it is defective, this can lead to a loss of cooling water.

Loss of cooling water at the pressure relief valve

To prevent the cooling system (hoses, tank, or radiator) from “bursting” under high load, there is a pressure relief valve in the lid of the expansion tank.

If the pressure rises too high, it opens and the hot steam or cooling water can escape from the system. A white cloud of water vapor then comes out of the engine compartment.

This can happen, for example, if the radiator fan is defective. In combination with a drive in the mountains at slow speed and high engine load, the engine or coolant temperature rises sharply. The airstream alone is no longer able to “remove” the heat in the radiator.

As a result, the pressure relief valve opens as described above. Caution: Again, never open the cap of the coolant reservoir. The system is under high pressure and there is a risk of severe burns.

It must be determined what the exact cause of this behavior is. If it is a defective cooling fan, for example, it must be repaired or replaced.

What is coolant made of?

Which cooling water may be used for one’s own car is precisely specified by the vehicle manufacturer.

Nowadays, in addition to low-calcium water, the cooling water also contains additives for corrosion and frost protection, among other things.

If you use cooling water that has not been approved by the vehicle manufacturer, this can lead to damage to the water pump and radiator, among other things. As a result, there is a risk of engine damage.


🔧 Where is the antifreeze filled?

The antifreeze is filled into the coolant tank. Caution: As long as the engine is still warm, the container must not be opened. The container is usually white or transparent and marked with the warning symbol against the risk of burns.

🔧 How is the antifreeze mixed?

The antifreeze is mixed with water. As a rule, the mixing ratio of water to antifreeze is 50:50 or 60:40. As a rule, the manufacturer prescribes the agent and the application. There are also ready-made mixtures to buy that already contain water. The antifreeze is checked with the cooling water spindle; if necessary, something must be added.

Important: Dumping pure antifreeze into the coolant tank is not a solution, because it only develops its full effect with water.

🔧 What happens if too much antifreeze is added?

If too much antifreeze is added, the optimum cooling capacity is no longer given. This is because the full cooling capacity only develops when mixed with water. If too much antifreeze is added, it can happen that not enough heat is dissipated. The result: the engine overheats and may even be damaged.

Checking coolant or antifreeze for beginners - Video

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Max Welder (rvneeded)

Max Welder (rvneeded)

Max Welder is a mechanic enthusiast. Currently, working at a small company. Experienced in electronics, car tools, and security systems. In his spare time, he writes articles for various blogs.

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