Coolant is essential for keeping your engine at the correct operating temperature. When the engine runs, it produces a lot of heat. The cooling system keeps this temperature under control and prevents the engine from overheating. In many cars, the normal operating temperature is around 90°C.
If the coolant level is too low, the engine may overheat. This can cause serious and expensive damage. A low coolant level can sometimes be solved by topping up the coolant, but in many cases it is a sign of a leak somewhere in the cooling system.
In this blog, we explain how the cooling system works, how to safely top up coolant, how long you should wait before topping it up, how to recognize a radiator leak or coolant leak, and what you can do to fix the problem yourself.
How does the cooling system work?
The cooling system prevents the engine from overheating. Coolant flows through the engine and absorbs heat. It then passes through the radiator, where the heat is released. The cooled fluid then circulates back through the engine.
Important parts of the cooling system include:
- the radiator;
- the water pump;
- the thermostat;
- coolant hoses;
- the cooling fan;
- the expansion tank;
- the temperature sensor.
If one of these components fails, the engine temperature can rise. A blockage, contamination or leak in the system can also prevent coolant from circulating properly.
Low coolant level: what does it mean?
A low coolant level means there is not enough coolant in the cooling system. You can usually check this by looking at the expansion tank under the bonnet. Most reservoirs have a minimum and maximum mark. If the level is below the minimum mark, you should take action.
A low coolant level can cause:
- rising engine temperature;
- reduced cabin heating;
- engine overheating;
- damage to the head gasket;
- damage to cylinders or pistons;
- a cracked cylinder head;
- serious engine damage in extreme cases.
Do not continue driving for long with a low coolant level. If the warning light comes on or the temperature gauge moves towards the red zone, stop the vehicle in a safe place as soon as possible.
How long should you wait before topping up coolant?
Never top up coolant while the engine is hot. The cooling system can be under pressure, and the coolant may be extremely hot. Opening the coolant reservoir cap too soon can cause hot steam or coolant to escape, which may result in burns.
As a rule, wait at least 30 minutes after switching off the engine before checking or topping up the coolant. If the engine has overheated, wait longer until the engine has cooled down properly.
Safe method:
- Park the car on a flat surface.
- Switch off the engine.
- Let the engine cool down.
- Open the bonnet.
- Carefully and slowly loosen the coolant reservoir cap.
- Top up the coolant to between the minimum and maximum marks.
- Tighten the cap securely.
- Check the level again after a short drive, once the engine has cooled down.
Can you top up coolant yourself?
Yes, in most cases you can top up coolant yourself. Make sure you use the correct coolant for your car. The right type can usually be found in the vehicle manual or checked based on the vehicle model.
Do not simply mix different types of coolant unless you are sure they are compatible. Using the wrong coolant can reduce protection against corrosion, freezing and overheating.
In an emergency, you may use water temporarily to prevent overheating, but this is not a long-term solution. Replace or dilute it with the correct coolant as soon as possible.
Can a car use coolant?
A car should not normally “use” coolant in the same way it uses fuel or engine oil. The cooling system is a closed system. This means the coolant should stay inside the system and circulate continuously.
If the coolant level keeps dropping, there is usually a reason. Possible causes include:
- a leaking radiator;
- a cracked or damaged coolant hose;
- a faulty hose clamp;
- a leaking water pump;
- a leaking thermostat housing;
- a leaking heater matrix;
- a faulty radiator cap;
- a leaking head gasket;
- internal coolant loss through the engine.
If you need to top up coolant regularly, there is likely a leak or another underlying problem that needs to be repaired.
How does coolant leakage occur?
Coolant leakage can occur in several places. In many cases, the cause is a worn or damaged part of the cooling system. A dried-out hose, loose clamp, damaged radiator or failing water pump can all lead to coolant loss.
Coolant can also disappear internally. This may happen when there is a leaking head gasket, a cracked cylinder head, a leak in the EGR cooler or a problem with the oil cooler.
Common causes of coolant leakage include:
- damaged coolant hoses;
- leaking radiator;
- leaking water pump;
- worn seals;
- loose or broken hose clamps;
- leaking heater radiator;
- cracked expansion tank;
- internal engine leakage.
Because the cooling system is closed, coolant should not disappear without a reason. If the level keeps dropping, leakage is the most likely explanation.
Radiator leak: how can you recognize it?
A radiator leak is one of the most common causes of coolant loss. The radiator is exposed to heat, pressure, road dirt and corrosion. Over time, small cracks or weak spots can develop.
Signs of a radiator leak include:
- coolant under the front of the car;
- a sweet smell around the engine bay;
- visible wet spots on or near the radiator;
- white residue around radiator seams;
- rising engine temperature;
- frequent need to top up coolant.
A small radiator leak can sometimes be temporarily fixed with a radiator stop leak additive. If the leak is large or the radiator is badly damaged, replacement may be necessary.
What are the risks of driving with a coolant leak?
Driving with a coolant leak can be risky. If too much coolant escapes, the engine can no longer be cooled properly. This may cause overheating and serious mechanical damage.
Possible consequences include:
- overheating engine;
- leaking head gasket;
- damaged pistons or cylinders;
- cracked cylinder head;
- warped engine components;
- damaged radiator or heater matrix;
- complete engine failure.
If the temperature gauge rises quickly or the warning light comes on, stop driving. Continuing to drive with an overheating engine can turn a small leak into a very expensive repair.
Can you continue driving with leaking coolant?
That depends on the severity of the leak and the coolant level. If the leak is minor and the temperature remains normal, you may be able to drive a short distance to a garage or safe location.
However, you should not continue driving if:
- the coolant warning light is on;
- the temperature gauge is in the red zone;
- steam is coming from under the bonnet;
- coolant is leaking heavily;
- the engine is running poorly;
- you need to top up coolant repeatedly.
Always keep an eye on the temperature gauge. If the engine starts to overheat, stop immediately and allow the engine to cool down.
Radiator cleaner: when should you use it?
A radiator cleaner is used to clean the inside of the cooling system. Over time, rust, scale, oil residue and other deposits can build up inside the radiator and coolant channels. This can reduce cooling performance and contribute to overheating.
A radiator cleaner can help when:
- the cooling system is contaminated;
- the engine runs hotter than normal;
- the radiator is partially blocked;
- old coolant has left deposits behind;
- you want to flush the system before adding fresh coolant.
A radiator cleaner does not repair leaks. It is meant to clean the system. If your coolant level keeps dropping, you should first check for leakage.
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Can you fix coolant leakage yourself?
In many cases, small coolant leaks can be treated with a radiator stop leak additive. This type of additive is designed to seal small leaks in the radiator, engine block or cooling system.
The Lindemann Radiator & Block Stop Leak is an additive that can help repair coolant leakage quickly and efficiently. It can be added to the cooling system and is suitable for almost all cooling systems. In addition to sealing small leaks, it also has a lubricating effect on seals and the water pump.
A stop leak additive can be a cost-effective first step, especially because garage repairs can be expensive. However, it is important to be realistic: if the leak is too large or a component is badly damaged, an additive may not be enough. In that case, the damaged part should be repaired or replaced.
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How much does coolant leakage repair cost?
The cost of repairing coolant leakage depends on the cause. Replacing a simple coolant hose is usually much cheaper than replacing a water pump, radiator or head gasket.
Examples of possible repairs include:
- replacing a hose or hose clamp;
- repairing or replacing the radiator;
- replacing the water pump;
- repairing the heater matrix;
- replacing a leaking head gasket.
Because labour costs can quickly add up, many drivers first try a suitable additive for small leaks. If the leak does not stop, professional diagnosis is recommended.
Step-by-step: what to do when your coolant level is low
- Stop the car safely if the warning light comes on or the engine temperature rises.
- Switch off the engine and let it cool down.
- Check the coolant level in the expansion tank.
- Top up with the correct coolant if the level is below minimum.
- Check under the car and around the engine bay for visible leaks.
- Monitor the temperature gauge while driving.
- If the coolant level drops again, inspect the system for leakage.
- Use a radiator cleaner only if the system is contaminated.
- Use a radiator stop leak additive only for small leaks.
- Visit a garage if the leak is severe or keeps returning.
Conclusion: topping up coolant is simple, but leakage should not be ignored
Topping up coolant is usually something you can do yourself, as long as the engine is cool and you use the correct coolant. However, coolant should not disappear from the system regularly. If you often need to top up coolant, there is probably a leak or another problem in the cooling system.
A low coolant level can lead to overheating and serious engine damage. Small leaks can sometimes be solved with a radiator stop leak additive, while contamination in the system can be treated with a radiator cleaner. If the leak is large, internal or keeps returning, professional repair is the safest option.
Do you have a leaking cooling system? Try a suitable radiator stop leak product first for small leaks, and always keep an eye on your coolant level and engine temperature.
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