Coolant: what does it mean?

What should you do about a low level?

Check the level as the handbook directs, typically with the engine cold. Do not open a hot system: pressurised fluid and steam can escape. If there is an overheating warning, follow the vehicle instructions and stop as soon as it is safe.

Look up the prescribed specification. Colour alone is not a reliable guide. Ask a garage what suits the car and its existing fill if you are unsure.

If you need repeated top-ups, have the cause investigated. Note when the level drops and whether there is a warning or visible leak. Repeatedly restoring the level does not resolve the underlying problem.

The level drops again

You noticed a low cold level last week and it has returned. Tell the garage about both readings. If an overheating warning appears while driving, follow the vehicle instructions immediately.

Check cold as directed and have repeated losses investigated.

Checking the specification and level safely

Coolant carries heat away and helps protect the system against freezing and corrosion. The required product depends on the car. Colour cannot establish whether two products are suitable for the same system. Check the handbook for the specification and any mixing requirements.

Check the level only under the specified conditions. A hot cooling system may be pressurised. Do not open the cap while it is hot and follow the instructions if a temperature warning appears.

Some cars have more than one reservoir under the bonnet. Use the handbook to identify the reservoir for the circuit you want to check. If the level is hard to see or you are unsure which filler you are looking at, ask a workshop to check it.

Recognising recurring coolant loss

After cooling system work, the reservoir level falls again in a short period. Tell the workshop when the work was done and which cold readings showed the change. A warm observation is difficult to compare with one made cold.

A single low reading and a level that falls after topping up tell you different things. Repeated loss calls for investigation of where the coolant is going.

Some products are sold as concentrate, while others are ready to use. Read the packaging to find out whether water needs to be added and in what proportion. If uncertain, ask what fluid is already in the car.

If you see an overheating warning or steam, follow the safety instructions and get help if unsure. Do not mix coolants without confirming what the vehicle allows.

Recording level, product and repair

Record the cold level, any warnings and the product the workshop used. After a repair, ask which part of the cooling system was checked.

If the cold level drops after a repair, tell the workshop which parts were replaced. Record whether you noticed dried marks or a puddle. Together with the point at which any warning appeared, this gives the technician more information than a photo of the reservoir alone.

If the car has more than one cooling circuit, identify the reservoir in the handbook. Different circuits can have separate checking procedures or fluid requirements.