How to top up engine coolant
Engine Coolant: How to Check It and Why It Matters
Every car uses engine coolant to help regulate engine temperature and keep it running smoothly. You should check your coolant level at least twice a year, ideally in early summer and winter.
Engine coolant absorbs heat from the engine and transfers it to the radiator where it cools down through airflow, preventing the engine from overheating.
This guide explains where to find your coolant tank, how to check the coolant level, and how to identify potential problems.
Where is the engine coolant tank?
The coolant tank location varies depending on the vehicle.
- If you are unsure where yours is located, check your vehicle handbook.
- The coolant reservoir is typically a semi-transparent plastic tank containing coloured liquid, with minimum (MIN) and maximum (MAX) level markings on the outside.
How to check engine coolant
1. Allow the engine to cool for at least 2 hours (overnight is best).
2. Never open the coolant cap while the engine is hot. The system is pressurised and hot steam or coolant can cause burns.
3. When the engine is cool, check the coolant level against the MIN and MAX markers on the tank.
4. If the level is below the minimum mark, your engine could overheat and the coolant should be topped up.
How to top up coolant
If tour engine coolant is low, top it up using the correct coolant mixture recommended for your vehicle.
Coolant can be purchased from petrol stations or motoring supply shops.
1. Slowly unscrew the coolant cap to release any pressure.
2. Fill the reservoir to the maximum mark, but do not overfill.
3. Secure the cap tightly once finished.
Overfilling can create excess pressure in the cooling system and may damage seals or cause the cap to release.
What does engine coolant do?
Engine coolant helps maintain the engine’s operating temperature.
It works by circulating through the engine and absorbing heat. The heated coolant then flows to the radiator, where airflow cools it before it returns to the engine.
Engine coolant is also essential as it:
- Prevents overheating.
- Protects against freezing in cold weather.
- Helps prevent corrosion inside the engine.
- Helps hybrid vehicles and EVs to cool their batteries and electrical systems.
You may hear the cooling fan running after the engine stops. This helps reduce coolant temperature and cool the engine.
When should engine coolant be changed?
Manufacturer guidance varies, although it typically lasts for 2 - 5 years, or 30,000 - 50,000 miles. However, coolant should be replaced regardless if you notice any of the following signs:
- Discolouration.
- Rust in the mixture.
- Contamination or debris.
If any of these appear, the coolant should be changed immediately.
Can I use water instead of coolant?
Water can be used only in an emergency to help you reach a garage. Using only water, rather than engine coolant, reduces cooling efficiency and protection.
Signs of an engine coolant problem
Common warning signs of issues with your engine coolant include:
- Rising temperature gauge on the dashboard.
- Temperature warning light.
- Engine overheating.
If you notice these signs, check your coolant level immediately.
If coolant is frequently low, there may be a leak in the cooling system. Inspect hoses, seals, clamps, and the coolant reservoir for residue or damage.
What to do if your engine overheats
If your engine overheats, you should:
1. Pull over safely as soon as possible.
2. Turn the engine off.
3. Allow the engine to cool before checking coolant levels.
4. Top up coolant or water if needed.
Do not continue driving if coolant is below the minimum level, as this could indicate a serious problem.
Turning off the air conditioning can reduce engine load if you need to drive to a garage.
Servicing and coolant checks
Regular servicing can help detect coolant issues early. At National Tyres, we perform a variety of vehicle services to keep your car running smoothly and safely.
To receive a coolant top up, engine oil and filter change, plus many more essential checks, book an interim service today. Or, upgrade to a full service or major service, and our experts will also check your coolant seals and hoses, and replace your air filter, plus cabin filter and break fluid (major service only).
Remember that during an MOT test, low coolant will not cause a failure, but it may be recorded as an advisory.
Book a service + MOT bundle for time and money saved, and an increased chance of passing your MOT as essential checks and top ups are carried out prior to the test.
If you need further advice, speak to a technician at your local National Tyres.
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